Fluvial channel belts, the deposits accumulated in rivers surrounded by floodplain deposits, are sensitive environmental recorders. Across Mars, wind has exposed ancient channel belts via the preferential erosion of floodplain strata, creating landforms called fluvial ridges. However, river deposits observed by the Mars rover Curiosity are instead exposed along a series of steep slopes and shallow benches, and short, truncated ridges we call noses. Here, we tested the hypothesis that these exposures record channel-belt exhumation with a preferential direction of scarp retreat (a slope-aspect control), in contrast with models of fluvial-ridge formation. Using a landscape evolution model sensitive to lithology and an Earth-analog 3D-seismic-reflectance volume imaging fluvial stratigraphy, we generated synthetic erosional landscapes where channel-belt exhumation created benches and noses rather than fluvial ridges, depending on the orientation of belts relative to the preferential direction of scarp retreat, which we suggest is set by winds steered along crater topography.
Surface-To-Ocean Exchange by the Sinking of Impact Generated Melt Chambers on...Sérgio Sacani
Impacts into icy bodies often generate near-surface melt chambers and thermal perturbations that soften the ice. We explore the post-impact evolution of non-penetrating impacts into Europa's ice shell. Simulations of viscous ice deformation show that dense impact melts founder before refreezing. If the transient cavity depth exceeds half the ice shell thickness, over 40% of the impact melt drains into the underlying ocean. Drainage of impact melts from the near-surface to the ocean occurs on timescales of 103–104 years. The drainage of melts to the ocean occurs for all plausible ice shell thicknesses and ice viscosities, suggesting that melt foundering is a natural consequence of impacts on icy worlds. Post-impact viscous deformation is an important process on icy worlds that affects cryovolcanism, likely modifies crater morphology, creates porous columns through the ice for surface-to-ocean exchange, and may supply the oxidants required for habitability to subsurface oceans.
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Ma...Sérgio Sacani
Valley networks are some of the strongest lines of evidence for
extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However,
their purported absence on certain ancient terrains, such as
Arabia Terra, is at variance with patterns of precipitation as predicted
by “warm and wet” climate models. This disagreement has contributed
to the development of an alternative “icy highlands” scenario,
whereby valley networks were formed by the melting of highland ice
sheets. Here, we show through regional mapping that Arabia Terra
shows evidence for extensive networks of sinuous ridges. We interpret
these ridge features as inverted fluvial channels that formed in
the Noachian, before being subject to burial and exhumation. The
inverted channels developed on extensive aggrading flood plains. As
the inverted channels are both sourced in, and traverse across, Arabia
Terra, their formation is inconsistent with discrete, localized sources
of water, such as meltwater from highland ice sheets. Our results are
instead more consistent with an early Mars that supported widespread
precipitation and runoff.
Using sea-floor morphometrics to constrain stratigraphic models of sinuous su...Aaron Reimchen
Constructing geologically accurate reservoir models of deep-water strata is challenging due to the reliance
on incomplete or limited resolution datasets. Connecting areas of high-certainty across areas where
data is sparse or non-existent (e.g., between wellbores) is difficult and requires numerous interpretations
and assumptions. In this study, morphometric data from the Lucia Chica Channel System, offshore California,
provides high-resolution 3-D information that is used to constrain correlation and characterization
of ancient submarine channel fill deposits.
Neotectonics concerns the study of horizontal and vertical crustal movements that have occurred in the geologically recent past and which may be ongoing today. Though most crustal movements arise directly or indirectly from global plate motions (i.e., tectonic deformation), neotectonic studies make no presumption about the mechanisms driving deformation. Consequently, ‘movements’ is a vague catch-all term that encompasses a myriad of competing deformation processes, such as the gradual pervasive creep of tectonic plates, discrete (seismic) displacements on individual faults and folds, and distributed tilting and warping through isostatic readjustment or volcanic upheaval. The phrase ‘geologically recent past’ is also appropriately vague. Early attempts to define the discipline by arbitrary time windows (e.g., Late Cenozoic, Neogene, or Quaternary) have given ground to a more flexible notion that envisages neotectonism starting at different times in different regions. The onset of the neotectonic period, or the ‘current tectonic regime’, depends on when the contemporary stress field of a region was first imposed. For instance, the current tectonic regime began in the Middle Quaternary (∼700 000 years ago) in the Apennines of central Italy, and even more recently (<500 000 years ago) in California; in contrast, in eastern North America, the present-day stress regime has been in existence for at least the past 15 million years.
Typically then, neotectonic movements have been in operation in most regions for the past few million years or so. Over such prolonged intervals, neotectonic actions are revealed by the stratigraphic build-up of sediments in inland and marine basins, the burial or exhumation histories of rocks, and the geomorphological development of landscapes. Geological studies of palaeobotany and palaeoclimate, numerical models of landscape evolution, and techniques such as fission-track analysis and cosmogenic dating are among the disparate tools unravelling this long-term tectonic activity. Over periods of many tens of to several hundreds of thousands of years, the actions of individual tectonic structures (faults and folds) can be determined, unmasked by their deformation of geomorphic markers, such as marine and fluvial terraces, and tracked with reference to the Late Pleistocene glacial–eustatic time-frame. The apparently smooth deformation rates discerned over intermediate time-scales are revealed to be episodic and irregular when faults and folds are examined over Holocene (10 000 years) time-scales. Over millennial time-scales, secular variations in the activity of tectonic structures can be gleaned from a diverse set of palaeoseismological approaches, from interpreting the stratigraphy of beds that have been affected by faulting, to detecting disturbances in the growth record of trees or coral atolls.
Distinguishing gas bearing sandstone reservoirs within mixed siliciclastic-ca...Ahmed Hafez
Seismic AVO analysis of the mixed clastics and carbonate sequences to distinguish the gas sandstone in the Nile Delta basin, offshore Mediterranean Sea. Rock physics analysis is also included. Extended elastic impedance inversion also applied. Nile Delta seismic reservoir characterization workflow
Surface-To-Ocean Exchange by the Sinking of Impact Generated Melt Chambers on...Sérgio Sacani
Impacts into icy bodies often generate near-surface melt chambers and thermal perturbations that soften the ice. We explore the post-impact evolution of non-penetrating impacts into Europa's ice shell. Simulations of viscous ice deformation show that dense impact melts founder before refreezing. If the transient cavity depth exceeds half the ice shell thickness, over 40% of the impact melt drains into the underlying ocean. Drainage of impact melts from the near-surface to the ocean occurs on timescales of 103–104 years. The drainage of melts to the ocean occurs for all plausible ice shell thicknesses and ice viscosities, suggesting that melt foundering is a natural consequence of impacts on icy worlds. Post-impact viscous deformation is an important process on icy worlds that affects cryovolcanism, likely modifies crater morphology, creates porous columns through the ice for surface-to-ocean exchange, and may supply the oxidants required for habitability to subsurface oceans.
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Ma...Sérgio Sacani
Valley networks are some of the strongest lines of evidence for
extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However,
their purported absence on certain ancient terrains, such as
Arabia Terra, is at variance with patterns of precipitation as predicted
by “warm and wet” climate models. This disagreement has contributed
to the development of an alternative “icy highlands” scenario,
whereby valley networks were formed by the melting of highland ice
sheets. Here, we show through regional mapping that Arabia Terra
shows evidence for extensive networks of sinuous ridges. We interpret
these ridge features as inverted fluvial channels that formed in
the Noachian, before being subject to burial and exhumation. The
inverted channels developed on extensive aggrading flood plains. As
the inverted channels are both sourced in, and traverse across, Arabia
Terra, their formation is inconsistent with discrete, localized sources
of water, such as meltwater from highland ice sheets. Our results are
instead more consistent with an early Mars that supported widespread
precipitation and runoff.
Using sea-floor morphometrics to constrain stratigraphic models of sinuous su...Aaron Reimchen
Constructing geologically accurate reservoir models of deep-water strata is challenging due to the reliance
on incomplete or limited resolution datasets. Connecting areas of high-certainty across areas where
data is sparse or non-existent (e.g., between wellbores) is difficult and requires numerous interpretations
and assumptions. In this study, morphometric data from the Lucia Chica Channel System, offshore California,
provides high-resolution 3-D information that is used to constrain correlation and characterization
of ancient submarine channel fill deposits.
Neotectonics concerns the study of horizontal and vertical crustal movements that have occurred in the geologically recent past and which may be ongoing today. Though most crustal movements arise directly or indirectly from global plate motions (i.e., tectonic deformation), neotectonic studies make no presumption about the mechanisms driving deformation. Consequently, ‘movements’ is a vague catch-all term that encompasses a myriad of competing deformation processes, such as the gradual pervasive creep of tectonic plates, discrete (seismic) displacements on individual faults and folds, and distributed tilting and warping through isostatic readjustment or volcanic upheaval. The phrase ‘geologically recent past’ is also appropriately vague. Early attempts to define the discipline by arbitrary time windows (e.g., Late Cenozoic, Neogene, or Quaternary) have given ground to a more flexible notion that envisages neotectonism starting at different times in different regions. The onset of the neotectonic period, or the ‘current tectonic regime’, depends on when the contemporary stress field of a region was first imposed. For instance, the current tectonic regime began in the Middle Quaternary (∼700 000 years ago) in the Apennines of central Italy, and even more recently (<500 000 years ago) in California; in contrast, in eastern North America, the present-day stress regime has been in existence for at least the past 15 million years.
Typically then, neotectonic movements have been in operation in most regions for the past few million years or so. Over such prolonged intervals, neotectonic actions are revealed by the stratigraphic build-up of sediments in inland and marine basins, the burial or exhumation histories of rocks, and the geomorphological development of landscapes. Geological studies of palaeobotany and palaeoclimate, numerical models of landscape evolution, and techniques such as fission-track analysis and cosmogenic dating are among the disparate tools unravelling this long-term tectonic activity. Over periods of many tens of to several hundreds of thousands of years, the actions of individual tectonic structures (faults and folds) can be determined, unmasked by their deformation of geomorphic markers, such as marine and fluvial terraces, and tracked with reference to the Late Pleistocene glacial–eustatic time-frame. The apparently smooth deformation rates discerned over intermediate time-scales are revealed to be episodic and irregular when faults and folds are examined over Holocene (10 000 years) time-scales. Over millennial time-scales, secular variations in the activity of tectonic structures can be gleaned from a diverse set of palaeoseismological approaches, from interpreting the stratigraphy of beds that have been affected by faulting, to detecting disturbances in the growth record of trees or coral atolls.
Distinguishing gas bearing sandstone reservoirs within mixed siliciclastic-ca...Ahmed Hafez
Seismic AVO analysis of the mixed clastics and carbonate sequences to distinguish the gas sandstone in the Nile Delta basin, offshore Mediterranean Sea. Rock physics analysis is also included. Extended elastic impedance inversion also applied. Nile Delta seismic reservoir characterization workflow
Prospects for Cryovolcanic Activity on Cold Ocean PlanetsSérgio Sacani
We have estimated total internal heating rates and depths to possible subsurface oceans for 17 planets that may be
cold ocean planets, low-mass exoplanets with equilibrium surface temperatures and/or densities that are consistent
with icy surfaces and a substantial H2O content. We have also investigated the potential for tidally driven
cryovolcanism and exosphere formation on these worlds. Estimated internal heating rates from tidal and radiogenic
sources are large enough that all planets in our study may harbor subsurface oceans, and their geological activity
rates are likely to exceed the geological activity rates on Jupiter’s moon Europa. Several planets are likely to
experience enhanced volcanic activity rates that exceed that of Io. Owing to their relatively thin ice shells and high
rates of internal heating, Proxima Cen b and LHS 1140 b are the most favorable candidates for telescopic detection
of explosive, tidally driven cryovolcanism. Estimates for thin ice shells on Proxima Cen b, LHS 1140 b, Trappist1f, and several Kepler planets suggest that any H2O vented into space during explosive cryovolcanic eruptions on
these worlds could be sourced directly from their subsurface oceans. Like the icy moons in our outer solar system,
cold ocean planets may be astrobiologically significant worlds that harbor habitable environments beneath their icy
surfaces. These possibilities should be considered during analyses of observational data for small exoplanets from
current and upcoming telescopes and during planning for a future space telescope mission aimed at characterization
of potentially habitable exoplanets (e.g., Habitable Worlds Observatory).
A deep groundwater origin for recurring slope lineae on MarsSérgio Sacani
The recurring slope lineae on Mars have been hypothesized to originate from snow melting, deliquescence, dry flow or shallow
groundwater. Except for the dry flow origin, these hypotheses imply the presence of surficial or near-surface volatiles, placing
the exploration and characterization of potential habitable environments within the reach of existing technology. Here we present observations from the High Resolution Imaging Science Experiment, heat-flow modelling and terrestrial analogues, which
indicate that the source of recurring slope lineae could be natural discharge along geological structures from briny aquifers
within the cryosphere, at depths of approximately 750 m. Spatial correlation between recurring slope lineae source regions and
multi-scale fractures (such as joints and faults) in the southern mid-latitudes and in Valles Marineris suggests that recurring
slope lineae preferably emanate from tectonic and impact-related fractures. We suggest that deep groundwater occasionally
surfaces on Mars in present-day conditions.
Martian soil as revealed by ground-penetrating radar at the Tianwen-1 landing...Sérgio Sacani
Much of the Martian surface is covered by a weathering layer (regolith or soil) produced
by long-term surface processes such as impact gardening, eolian erosion, water weathering,
and glacial modifications. China’s first Martian mission, Tianwen-1, employed the Mars
Rover Penetrating Radar (RoPeR) to unveil the detailed structure of the regolith layer and
assess its loss tangent. The RoPeR radargram revealed the local regolith layer to be highly
heterogeneous and geologically complex and characterized by structures that resemble partial
or complete crater walls and near-surface impact lenses at a very shallow depth. However,
comparable radar data from the Lunar far side are rather uniform, despite the two surfaces
being geologically contemporary. The close-to-surface crater presented in this study shows
no detectable surface expression, which suggests an accelerated occultation rate for small
craters on the surface of Mars as compared to the rate on the Moon. This is probably due to
the relentless eolian processes on the Martian surface that led to the burial of the crater and
thus shielded it from further erosion. The high loss tangent indicates that the regolith at the
Tianwen-1 landing site is not dominated by water ice.
A Morphological and Spatial Analysis of Volcanoes on VenusSérgio Sacani
Venus is home to many thousands of volcanic landforms that range in size from much less than 5 km to well over 100 km in diameter. Volcanism is clearly a major, widespread process on Venus, and is a principal expression of the planet's secular loss of interior heat. Without sufficient in situ data to clearly determine its internal structure, we can use the morphological and spatial properties of volcanoes across the planet to help place constraints on our understanding of the volcanic characteristics and history of Venus. With the Magellan synthetic-aperture radar full-resolution radar map left- and right-look global mosaics at 75 m-per-pixel resolution, we developed a global catalog of volcanoes on Venus that contains ∼85,000 edifices, ∼99% of which are <5 km in diameter. We find that Venus hosts far more volcanoes than previously mapped, and that although they are distributed across virtually the entire planet, size–frequency distribution analysis reveals a relative lack of edifices in the 20–100 km diameter range, which could be related to magma availability and eruption rate. Through spatial density analysis of volcanoes alongside assessments of geophysical data sets and proximal tectonic and volcanic structures, we report on the morphological and spatial patterns of volcanism on Venus to help gain new insights into the planet's geological evolution
Topograp hic Constraints on the Evolution and Connectivityof Titan’ s Lacustr...Sérgio Sacani
The topography provided by altimetry, synthetic aperture radar-topography, and stereoradargrammetry has opened new doors for Titan research by allowing for quantitative analysis ofmorphologic form. Using altimetry measurements, we show that Titan’s Maria are consistent with anequipotential surface but that several filled lakes are found to be hundreds of meters above this sea level,suggesting that they exist in isolated or perched basins. Within a given drainage basin, empty lake floors aretypically higher than the liquid elevation of nearby lakes/seas, suggesting local subsurface connectivity.The majority of Titan’s lakes reside in topographically closed, sharp-edged depressions whose planformcurvature suggests lateral expansion through uniform scarp retreat. Many, but not all, empty lake basinsexhibit flat floors and hectometer-scale raised rims that present a challenge to formation models. Weconclude that dissolution erosion can best match the observed constraints but that challenges remain inthe interpretation of formation processes and materials.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
More Related Content
Similar to Landforms Associated With the Aspect-Controlled Exhumation of Crater-Filling Alluvial Strata on Mars
Prospects for Cryovolcanic Activity on Cold Ocean PlanetsSérgio Sacani
We have estimated total internal heating rates and depths to possible subsurface oceans for 17 planets that may be
cold ocean planets, low-mass exoplanets with equilibrium surface temperatures and/or densities that are consistent
with icy surfaces and a substantial H2O content. We have also investigated the potential for tidally driven
cryovolcanism and exosphere formation on these worlds. Estimated internal heating rates from tidal and radiogenic
sources are large enough that all planets in our study may harbor subsurface oceans, and their geological activity
rates are likely to exceed the geological activity rates on Jupiter’s moon Europa. Several planets are likely to
experience enhanced volcanic activity rates that exceed that of Io. Owing to their relatively thin ice shells and high
rates of internal heating, Proxima Cen b and LHS 1140 b are the most favorable candidates for telescopic detection
of explosive, tidally driven cryovolcanism. Estimates for thin ice shells on Proxima Cen b, LHS 1140 b, Trappist1f, and several Kepler planets suggest that any H2O vented into space during explosive cryovolcanic eruptions on
these worlds could be sourced directly from their subsurface oceans. Like the icy moons in our outer solar system,
cold ocean planets may be astrobiologically significant worlds that harbor habitable environments beneath their icy
surfaces. These possibilities should be considered during analyses of observational data for small exoplanets from
current and upcoming telescopes and during planning for a future space telescope mission aimed at characterization
of potentially habitable exoplanets (e.g., Habitable Worlds Observatory).
A deep groundwater origin for recurring slope lineae on MarsSérgio Sacani
The recurring slope lineae on Mars have been hypothesized to originate from snow melting, deliquescence, dry flow or shallow
groundwater. Except for the dry flow origin, these hypotheses imply the presence of surficial or near-surface volatiles, placing
the exploration and characterization of potential habitable environments within the reach of existing technology. Here we present observations from the High Resolution Imaging Science Experiment, heat-flow modelling and terrestrial analogues, which
indicate that the source of recurring slope lineae could be natural discharge along geological structures from briny aquifers
within the cryosphere, at depths of approximately 750 m. Spatial correlation between recurring slope lineae source regions and
multi-scale fractures (such as joints and faults) in the southern mid-latitudes and in Valles Marineris suggests that recurring
slope lineae preferably emanate from tectonic and impact-related fractures. We suggest that deep groundwater occasionally
surfaces on Mars in present-day conditions.
Martian soil as revealed by ground-penetrating radar at the Tianwen-1 landing...Sérgio Sacani
Much of the Martian surface is covered by a weathering layer (regolith or soil) produced
by long-term surface processes such as impact gardening, eolian erosion, water weathering,
and glacial modifications. China’s first Martian mission, Tianwen-1, employed the Mars
Rover Penetrating Radar (RoPeR) to unveil the detailed structure of the regolith layer and
assess its loss tangent. The RoPeR radargram revealed the local regolith layer to be highly
heterogeneous and geologically complex and characterized by structures that resemble partial
or complete crater walls and near-surface impact lenses at a very shallow depth. However,
comparable radar data from the Lunar far side are rather uniform, despite the two surfaces
being geologically contemporary. The close-to-surface crater presented in this study shows
no detectable surface expression, which suggests an accelerated occultation rate for small
craters on the surface of Mars as compared to the rate on the Moon. This is probably due to
the relentless eolian processes on the Martian surface that led to the burial of the crater and
thus shielded it from further erosion. The high loss tangent indicates that the regolith at the
Tianwen-1 landing site is not dominated by water ice.
A Morphological and Spatial Analysis of Volcanoes on VenusSérgio Sacani
Venus is home to many thousands of volcanic landforms that range in size from much less than 5 km to well over 100 km in diameter. Volcanism is clearly a major, widespread process on Venus, and is a principal expression of the planet's secular loss of interior heat. Without sufficient in situ data to clearly determine its internal structure, we can use the morphological and spatial properties of volcanoes across the planet to help place constraints on our understanding of the volcanic characteristics and history of Venus. With the Magellan synthetic-aperture radar full-resolution radar map left- and right-look global mosaics at 75 m-per-pixel resolution, we developed a global catalog of volcanoes on Venus that contains ∼85,000 edifices, ∼99% of which are <5 km in diameter. We find that Venus hosts far more volcanoes than previously mapped, and that although they are distributed across virtually the entire planet, size–frequency distribution analysis reveals a relative lack of edifices in the 20–100 km diameter range, which could be related to magma availability and eruption rate. Through spatial density analysis of volcanoes alongside assessments of geophysical data sets and proximal tectonic and volcanic structures, we report on the morphological and spatial patterns of volcanism on Venus to help gain new insights into the planet's geological evolution
Topograp hic Constraints on the Evolution and Connectivityof Titan’ s Lacustr...Sérgio Sacani
The topography provided by altimetry, synthetic aperture radar-topography, and stereoradargrammetry has opened new doors for Titan research by allowing for quantitative analysis ofmorphologic form. Using altimetry measurements, we show that Titan’s Maria are consistent with anequipotential surface but that several filled lakes are found to be hundreds of meters above this sea level,suggesting that they exist in isolated or perched basins. Within a given drainage basin, empty lake floors aretypically higher than the liquid elevation of nearby lakes/seas, suggesting local subsurface connectivity.The majority of Titan’s lakes reside in topographically closed, sharp-edged depressions whose planformcurvature suggests lateral expansion through uniform scarp retreat. Many, but not all, empty lake basinsexhibit flat floors and hectometer-scale raised rims that present a challenge to formation models. Weconclude that dissolution erosion can best match the observed constraints but that challenges remain inthe interpretation of formation processes and materials.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Deep Behavioral Phenotyping in Systems Neuroscience for Functional Atlasing a...Ana Luísa Pinho
Functional Magnetic Resonance Imaging (fMRI) provides means to characterize brain activations in response to behavior. However, cognitive neuroscience has been limited to group-level effects referring to the performance of specific tasks. To obtain the functional profile of elementary cognitive mechanisms, the combination of brain responses to many tasks is required. Yet, to date, both structural atlases and parcellation-based activations do not fully account for cognitive function and still present several limitations. Further, they do not adapt overall to individual characteristics. In this talk, I will give an account of deep-behavioral phenotyping strategies, namely data-driven methods in large task-fMRI datasets, to optimize functional brain-data collection and improve inference of effects-of-interest related to mental processes. Key to this approach is the employment of fast multi-functional paradigms rich on features that can be well parametrized and, consequently, facilitate the creation of psycho-physiological constructs to be modelled with imaging data. Particular emphasis will be given to music stimuli when studying high-order cognitive mechanisms, due to their ecological nature and quality to enable complex behavior compounded by discrete entities. I will also discuss how deep-behavioral phenotyping and individualized models applied to neuroimaging data can better account for the subject-specific organization of domain-general cognitive systems in the human brain. Finally, the accumulation of functional brain signatures brings the possibility to clarify relationships among tasks and create a univocal link between brain systems and mental functions through: (1) the development of ontologies proposing an organization of cognitive processes; and (2) brain-network taxonomies describing functional specialization. To this end, tools to improve commensurability in cognitive science are necessary, such as public repositories, ontology-based platforms and automated meta-analysis tools. I will thus discuss some brain-atlasing resources currently under development, and their applicability in cognitive as well as clinical neuroscience.
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
2. Geophysical Research Letters
CARDENAS AND STACEY
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sets of steep slopes with sediment cover (17 ± 6°) that transition to shallower benchtops (5 ± 3°; Cardenas
et al., 2022a). These benches extend for 10–100 s of m at the Glasgow member (Figure 1). At the Mercou member
outcrops, the rock is exposed along two features akin to truncated fluvial ridges, which we call noses (Figure 1).
These noses have near-vertical front cliffs and are flanked by slopes with similar dips to bench slopes (∼10–20°;
Cardenas et al., 2022a).
We suspect that the formation of bench-and-slope and nose topography from the erosion of fluvial strata, rather
than fluvial ridges, might be unique to crater-filling strata. Winds in craters with actively eroding fills have been
found to be unidirectional at locations, steered by crater topography (Day et al., 2016), though with seasonal-
ity (Cornwall et al., 2018). If unimodal winds are associated with a preferred direction of scarp retreat, and if
eolian erosion rates are also sensitive to lithology as has been shown on Earth and Mars (Pain et al., 2007; Pain
Oilier, 1995; Williams et al., 2007), we hypothesize this may generate landforms distinct from fluvial ridges
Figure 1. Bench-and-slope and nose morphologies of the Carolyn Shoemaker formation. Panels (a and b) are from HiRISE image PSP_009149_1750. Elevation
contours are shown at 5 m intervals in white. (a) Red circle and arrows show the rover location and the extent of the mosaic in panel (c). (b) Mercou member. Red
circle and arrows show the rover location and the extent of the mosaic in panel (d). (c) Glasgow member. Bench-and-slope morphology from the ground. Mosaic from
Curiosity rover Mastcam sequence 15302, mission sol 2933. (d) Nose morphology from the ground at the Mont Mercou outcrop. Mosaic from Curiosity rover Mastcam
sequence 15933, mission sol 3051. (Mastcam image credit: NASA/Caltech-JPL/MSSS).
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3. Geophysical Research Letters
CARDENAS AND STACEY
10.1029/2023GL103618
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during the erosion of alluvial stratigraphy. Indeed, lithology and slope-aspect are recognized as factors that can
influence landscape evolution on Earth (e.g., Istanbulluoglu et al., 2008; Pelletier et al., 2018), but have not been
explored in the context of exhumed alluvial stratigraphy on Mars.
2. Methods
To test the hypothesis that a preferred direction of scarp retreat creates noses and benches instead of fluvial
ridges, we used a landscape evolution model with a preferred direction of scarp retreat, and applied this model to
earth-analog fluvial stratigraphy imaged in a 3D seismic reflectance volume imaging floodplain and channel-belt
deposits beneath the Gulf of Mexico seafloor (Cardenas et al., 2023). This volume was selected because it images
channel belts at multiple stratigraphic levels stacked in complicated patterns, similar to fully exposed fluvial
stratigraphy across Mars (e.g., DiBiase et al., 2013) and Earth (Hartley et al., 2015), and thus representative of
fluvial stratigraphy in general. We modified an existing landscape-evolution model (Cardenas et al., 2022b) built
using Landlab (Barnhart et al., 2020; Hobley et al., 2017). The original model generated fluvial ridges from
alluvial stratigraphy imaged in a 3D seismic reflectance volume by setting local erosion rates and diffusivities
to be a function of a lithology proxy taken from the seismic volume. Here, our modification added slope aspect,
the azimuth direction of steepest descent, as a control on local erosion rates. We defined an aspect of maximum
erosion, θm. Cells with aspects not oriented toward θm had their erosion rates decreased based on their arc distance
from θm.
The 3D seismic volume used as the original stratigraphy in the erosional model is a section of volume B-11-92-LA
and is available for free at the United States Geological Survey-managed National Archive of Marine Seismic
Surveys website (https://walrus.wr.usgs.gox/NAMSS/). Depth in this volume is given in terms of milliseconds
of two-way-travel time. We assumed 1 millisecond of two-way-travel time equaled 1 m of thickness (Armstrong
et al., 2014; Straub et al., 2009). As input, we used a seismic attribute called sweetness normalized by its maxi-
mum value, which we called Ω. This value represents the relative proportion of sandstone to mudstone at a
location, and is useful for identifying the sandstone-rich channel belts surrounded by mudstone-rich floodplains
in seismic volumes (Hart, 2008). In this volume, channel belts are oriented north-south and east-west, with local
variability (Figure 2). Using techniques to measure local channel-belt orientations (Cardenas Lamb, 2022), we
found a mean orientation toward 192°, with a standard deviation of 57° (n = 2,923 points evenly spaced along
26 belt segments). We ran three experiments designed to place aspects of maximum erosion equal to, oblique to,
and normal to the mean belt orientation. In experiments 1–3, θm was set to 192°, 237°, and 282°, respectively.
2.1. Model Derivation
Erosion rates in the landscape evolution model are defined by two terms applied to an initially smooth, horizontal
surface with closed boundaries:
−
𝑑𝑑𝑑𝑑
𝑑𝑑𝑑𝑑
= 𝐸𝐸𝑎𝑎 + 𝐸𝐸𝑑𝑑
(1)
In Equation 1, z is elevation, t is time, Ea is a landscape-lowering rate which we take to represent erosion driven
by eolian sand abrasion, and Ed is the landscape change driven by topographic diffusion. Ed preserves mass, but
Ea only removes material. The net erosion of Ea is reasonable because sediment transport is active on Mars, and
thus locations like Gale crater have widespread outcrops not covered in loose sediment. The spatially variable
sandstone-to-mudstone ratio (Ω) throughout the volume was set by the locations of fluvial channel belts and
produced an erosional landscape with relief when Equation 1 was applied to the stratigraphic volume. The term Ea
assumes that a higher sandstone content implies a lower erosion rate (Hayden et al., 2019; Sklar Dietrich, 2001;
Williams et al., 2007). Here, we added an additional term, α, that decreases this erosion rate depending on local
aspect (slope azimuth direction).
𝐸𝐸𝑎𝑎 =
𝐾𝐾1
Ω𝑚𝑚
𝛼𝛼
(2)
Here, α is a function of θ and the exponent p. Constants K1 and m were set to 1 L/T and 2, respectively. We
set m = 2 because erosion rate scales inversely squared with tensile strength for abrasion processes driven by
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repetitive impacts (Sklar Dietrich, 2001), under the assumption that tensile strength is proportional to Ω
(Cardenas et al., 2022b).
𝛼𝛼 = (1 − 𝜃𝜃)𝑝𝑝
(3)
The term θ is the angular distance between the aspect of maximum erosion, θm, and the local aspect, θl, in degrees.
We set p = 5 to enhance the erosion-rate decrease away from θm, but a true representative value is unknown.
Figure 2. Seismic volume and orientation of channel belts. (a) Six horizontal slices of increasing depth in the seismic
volume. Yellow is sandstone rich, black is mudstone rich. (b) Rose diagram showing the distribution of local channel-belt
orientations in the downstream direction, as well as the preferred scarp-retreat directions for each of the three experiments
(toward the mean, and 45° and 90° clockwise from the mean.
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𝜃𝜃 =
|𝜃𝜃𝑚𝑚 − 𝜃𝜃𝑙𝑙|
180
(4)
Here, |θm−θl| ≤ 180. When local aspect is approaching the aspect of maximum erosion, θl → θm, θ → 0 (Equa-
tion 4), α → 1 (Equation 3), and
𝐴𝐴 𝐴𝐴𝑎𝑎 →
𝐾𝐾1
Ω𝑚𝑚
(Equation 2). When local aspect is approaching a maximum 180° away
from the aspect of maximum erosion, θm ≫ θl, θ→1 (Equation 4), α → 0 (Equation 3), and Ea → 0 (Equation 2).
This establishes a preferential direction for scarp retreat in the direction opposite θm, which we call ¬θm.
The second process was topographic diffusion representing hillslope creep, freeze-thaw cycles, and microim-
pacts, with diffusivity set by the sandstone-to-mudstone ratio such that mudstones form hillslopes and sandstones
form steeper cliffs. We did not set an aspect control on diffusion.
𝐸𝐸𝑑𝑑 = −𝐾𝐾2∇2
𝑧𝑧
(5)
Here, K2 was diffusivity (L2
/T), and ∇2
z was local topographic curvature (1/L). The diffusivity, K2, varied with Ω.
𝐾𝐾2 =
𝐾𝐾3
Ω𝑛𝑛
(6)
The constant n was set to 1. For the experiment that produced the results shown in Figure 3, we set K1 = 1 (L/T;
Equation 2) and K3 = 0.5 (L2
/T; Equation 6). We tested the sensitivity of model results to variations in K1 and K3
(Figure S1 in Supporting Information S1), but here focus discussion on the values above because they produced
the most familiar landforms and thus, we assume, best represent processes at Gale crater. We emphasize that
absolute erosion rates are unknown and the results we present are only sensitive to the relative erosion rates set
by
𝐴𝐴
𝐾𝐾1
𝐾𝐾3
. For this reason, we present model runtimes in model steps rather than years.
3. Results
Here, we present a landscape from each experiment near the 2000th model step (Figure 3). These steps were
selected because the landscapes expose channel belts from different stratigraphic levels, and the topographic
surface minimally intersects the bottom of the domain. None of the landscapes feature recognizable fluvial
ridges, though fluvial ridges were generated in experiments featuring high
𝐴𝐴
𝐾𝐾1
𝐾𝐾3
presented in Figure S1 in Support-
ing Information S1, which we will not discuss further. To identify benches and noses, we used slope maps set to
highlight slopes of at least 11° (Figures 3d–3f), similar to the minimum slopes observed on Mars (Figure 1). We
also used changes in contour spacing to identify shallower bench and nose edges.
Each experiment produced recognizable benches and noses, as hypothesized (Figure 3). The locations where these
landforms developed was sensitive to local channel-belt curvature and the aspect of maximum erosion, θm. No
experiment particularly favored the development of either benches or noses. Channel-belt reaches were oriented
relative to θm such that both landforms were produced in each experiment. Benches formed where channel-belt
segments were oriented close to perpendicular to θm, but benches also curved away from this orientation, reflect-
ing belt geometry (Figure 3). Segments oriented into θm were associated with noses, which are reminiscent of
fluvial ridges with eroded tips (Figure 3). There were no examples of noses oriented toward ¬θm, though some
noses transition into benches, again reflecting channel-belt curvature, or the curvature of stacked channel belts as
is the case in the example shown in experiment 3 (Figure 3c). Several nose flanks had an asymmetrical drop in
topography on either margin, with only one flank meeting the 11° threshold (Figures 3d and 3e). Experiment 3
has a well-formed nose with both flanks meeting this cutoff (Figure 3f).
The relief associated with benches and noses is a function of their location relative to other sandstones and
θm. The largest benches in these experiments are not necessarily formed from the highest-Ω exposures (e.g.,
Figure 3). Instead, the largest benches are generated at the first major Ω peak (Ω ≥ 0.3) in the direction of ¬θm for
several km. For example, the largest Ω peak in experiment 1 transect A-A′ (Ω = 0.6; Figures 3g and 3h) forms a
m-scale bench superimposed on a larger bench formed ∼2 km toward θm from a smaller Ω (Ω = 0.5). Essentially,
the first Ω peak in a series of Ω peaks forms a protective shadow that decreases the total erosion for km behind
the first bench. This can also be seen in Figures 3a–3c, where many exposed sandstones are not associated with
significant topography visible in the 5 m contours. This sheltering is the product of slopes oriented toward ¬θm
being modified primarily by diffusive processes (Equation 1), and is the primary factor distinguishing this model
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Figure 3. Hillshade maps of synthetic landscapes with 5- and 20-m contours. θm values are shown. Hillshade illumination is from the east. Colorized topography is
draped on the hillshade, and overlain with red and yellow values showing Ω. A bench and nose are pointed to in each experiment. Light blue arrows point to high- Ω
locations not associated with steep topography. (a) Experiment 1, model step 1964. (b) Experiment 2, model step 1996. (c) Experiment 3, model step 2001. A transition
between a bench and a nose is marked. (d) Slope map of panel a showing slopes ≥11°, near the minimum slope defining bench and nose margin slopes on Mars.
Benches show up well, but the labeled nose has only its eastern flank shown. (e) Slope map of panel (b). Similarly, benches are well represented, but only the southern
flank of the nose is steep enough to be shown. (f) Slope map of panel (c). Here, the bench, bench-nose transition, and both nose flanks show up well. Both nose flanks
are very closely oriented toward θm. (g) Topography (black line) and Ω (red line) along the profile A-A′ in panel (a). Large arrows point to benches and noses with 10 s
of m of relief. Small arrows point to benches and noses with m of relief. (h) Topography (black line) and Ω (red line) along the profile B-B′ in panel (a).
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of bench formation from models of fluvial-ridge formation (Cardenas et al., 2022b; Hayden Lamb, 2020).
Noses can show a similar sheltering effect, slowing the eolian erosion of deposits behind a narrow high-Ω loca-
tion in the direction ¬θm, even forming at locations where this does not match channel-belt orientation (Figure 3).
This further distinguishes noses generated here from fluvial ridges, which form specifically from the highest-Ω
deposits (Cardenas et al., 2022b). Though most topography in the results can be explained by the outcrop at the
same timestep or this shadowing effect, there may also be lingering responses to topography generated by fully
eroded rock.
The three landscapes show similar general responses to their respective θm values, despite their different relation-
ships to mean channel-belt orientation. In each landscape, the distribution of aspects is bimodal, oriented toward
¬θm ± 90° (Figure 4). However, the aspects of slopes ≥11°, which define belt and nose edges, are in contrast
oriented toward θm ± 90° (Figure 4). This represents bench edges mostly oriented toward θm with significant
mapview curvature, and nose flanks oriented perpendicular to θm. Experiment three has a relative abundance of
north-facing steep slopes (Figure 4c). Ultimately, the erosion of slopes with aspects near θm actually leads to the
preservation of these slope aspects, as they cannot be diffusively filled. As lithology boundaries, and thus steep
slopes, do not dominate the landscape, the slopes oriented toward θm ± 90° are underrepresented as a whole and
overrepresented among steep slopes (Figure 4).
4. Discussion
The synthetic erosional landscapes we generated here have similarities to the exposures of alluvial strata in the
Glasgow and Mercou members of the Carolyn Shoemaker formation in Gale crater (Figure 1). Most impor-
tantly, our synthetic landscapes feature benches and noses, rather than fluvial ridges, supporting our hypothesis
(Figure 3). As was interpreted at the Glasgow member (Cardenas et al., 2022a), bench curvature can approx-
imately follow the curvature of sandstone bodies for 10–100 s of m (Figure 3). At the landscape scale, the
bimodal distribution of slope aspects is similar to the distribution of scarp orientations measured at Gale and
Jezero (Williams et al., 2020, their Figure 3). Though not as clearly bimodal as our synthetic landscapes, scarp
orientations at Gale crater, Jezero crater, and the Jezero delta do feature two dominant opposing quadrants, a third
more populated quadrant, and a final least populated quadrant, similar to our results (Figure 4). The Jezero floor
does not feature this pattern (Williams et al., 2020, their Figure 3c), and may not be sedimentary in origin (Farley
et al., 2022).
Differences between our synthetic landscapes and the Carolyn Shoemaker formation outcrops exist as well. The
primary difference is in scale. The largest benches we produced are 10 s of m high (Figure 3), comparable to the
entire height of the 5–6 benches at the Glasgow member outcrop (Figure 1a). This is likely related to the scale of
the original stratigraphic volume and the thickness of channel belts. Sandstone bodies at the Glasgow member
were 1.3 m thick at their thickest exposure, and benches were 10 s of m wide (Cardenas et al., 2022a, their Figure
9). Similarly, Mont Mercou and the adjacent nose are under 100 m in length, whereas many noses generated in
these experiments extend 100 s of m (Figure 3). The seismic volume, on the other hand, has a vertical resolution
of 4 m, thicker than the thickest sandstone measured at the benches and more than half the height of the Mont
Mercou outcrop (Figure 1). Further, the lateral resolution of the seismic volume is 20 m, and thus a few pixels at
best may represent bench width at the Carolyn Shoemaker formation exposures. The channel belts that are imaged
in the seismic survey are wide enough and thick enough to exceed this resolution limit, generating larger land-
forms that nonetheless relate to their underlying stratigraphy in the same ways. Despite this scale difference, our
model produces similar landscape bench and nose slopes to those observed at the Carolyn Shoemaker formation
(e.g., 11°; Figure 1; Cardenas et al., 2022a). This suggests our mix of eolian and diffusive processes, represented
by our selected
𝐴𝐴
𝐾𝐾1
𝐾𝐾3
, is reasonably representative of Gale crater.
Though this landscape-evolution model is primarily geometric and we did not explicitly model a wind direction,
we interpret θm to represent a particular unimodal wind regime that promotes erosion of θm-facing slopes. Winds
in craters are steered in preferential directions by crater topography (Day Dorn, 2019; Dromart et al., 2021),
and are capable of driving significant erosion of crater-filling stratigraphy (Day et al., 2016; Sullivan et al., 2022).
Erosion of crater-filling strata tends to initiate along the inner rim and extend over time toward the center of the
crater, leading to channelized and presumably unimodal winds (Day et al., 2016). This topographic steering of
eroding winds and the establishment of a preferential direction for scarp retreat may be the reason why fluvial
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ridges are not forming as the Carolyn Shoemaker formation erodes, despite containing the prerequisite alluvial
stratigraphy (Caravaca et al., 2022, Cardenas et al., 2022a; Fedo et al., 2022). Examples of craters that do contain
fluvial ridges have fills that have been heavily exhumed already (Day et al., 2019; Goudge et al., 2018; Jerolmack
et al., 2004), possibly diminishing the steering of winds between crater walls and less-eroded crater mounds.
Figure 4. Rose diagrams showing slope aspects for the entire landscape (left) and the bench and nose-forming slopes (≥11°,
right). Red arrows show the fastest-eroding aspects for each experiment. (a) Results from experiment 1. (b) Results from
experiment 2. (c) Results from experiment 3.
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Indeed, most fluvial ridges on Mars are not located in craters, and are instead found in the intra-crater plains
(Dickson et al., 2020) or at the margin of the martian topographic dichotomy (Burr et al., 2009; Cardenas
Lamb, 2022; Davis et al., 2019). Similarly, a version of the erosion model applied here but with no aspect control
on erosion rates produced fluvial ridges (Cardenas et al., 2022b).
Our synthetic landscapes suggest that alluvial stratigraphy might be heretofore unrecognized in crater fill,
exposed as topographic benches and noses that are far more subtle than fluvial ridges (Burr et al., 2009; Williams
et al., 2013b). It is noted that benches in particular may be qualitatively, and perhaps even quantitatively, similar
to landforms that are associated with the erosion of homogeneous underlying strata (Montgomery et al., 2012;
Stack et al., 2022). This highlights some of the challenges of using remote-sensing data to interpret depositional
settings (as recently discussed in Fedo et al., 2022). However, our results also provide some paths forward. For
instance, while topographic benches and slopes observed at HiRISE scale appear similar to periodic bedrock
ridges (Stack et al., 2022), the presence of both benches and noses may be uniquely related to the erosion of
alluvial stratigraphy, or deposits from another channelized sedimentary system. Further, exhumed coarse-grain
rocks including sandstones tend to appear bright in nighttime thermal images due to their high thermal inertia
(e.g., Burr et al., 2010), and our experiments suggest these hard lithologies should outcrop at benches and noses.
Because our example features are 10–100 s of m in scale and thus detectable with Mars remote sensing datasets,
this may assist with future investigations of the stratigraphy of crater-fill, as well as with laterally tracing the
Carolyn Shoemaker formation across Mount Sharp using HiRISE images and stereo topography.
5. Conclusions
Here, we modeled the Mars-like erosion of alluvial strata imaged in an analog 3D seismic reflectance volume.
We set local landscape-lowering rates to be a function of lithology, slope, and slope aspect, which set a preferen-
tial direction of scarp retreat. We generated synthetic erosional landscapes that formed topographic benches and
noses, rather than fluvial ridges, where channel belts were exhumed. The erosional patterns are similar to those
observed by the Curiosity rover at the alluvial deposits of the Carolyn Shoemaker formation in Gale crater, where
there is a record of crater topography steering winds. Thus, we predict that alluvial strata may be located in other
crater fill on Mars, exposed as subtle benches and noses rather than fluvial ridges.
Data Availability Statement
The Python scripts used to run the model, the numpy array containing the seismic volume, and all results from our
experiments are available on Penn State's ScholarSphere repository (Cardenas, 2023). The experiments labeled
1–3 here refer to experiments 7–9 in the complete data set.
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Acknowledgments
We thank editor Harihar Rajaram,
and Jeff Nittrouer and an anonymous
reviewer for their constructive reviews.
Mike Lamb, John Grotzinger, and
Maddy Turner all provided helpful
discussions during the early stages of
this project. This work was funded by
NASA Solar System Workings Grant
80NSSC22K1381 awarded to Cardenas.
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