The document summarizes research on the Sheepbed mudstone sample collected by the Curiosity rover in Gale crater on Mars. Key points:
- Potassium-argon dating of the mudstone yielded an age of 4.21 ± 0.35 billion years, consistent with the expected antiquity of rocks in Gale crater.
- Cosmogenic neon-21, helium-3, and argon-36 isotopes in the mudstone yielded concordant surface exposure ages of 78 ± 30 million years, indicating recent exposure by wind erosion rather than during initial transport and deposition.
- The mudstone's composition and mineralogy suggest it has not been heated above 200°C and may preserve
Craters, boulders and regolith of (101955) Bennu indicative of an old and dyn...Sérgio Sacani
Small, kilometre-sized near-Earth asteroids are expected to have young and frequently refreshed surfaces for two reasons:
collisional disruptions are frequent in the main asteroid belt where they originate, and thermal or tidal processes act on them
once they become near-Earth asteroids. Here we present early measurements of numerous large candidate impact craters on
near-Earth asteroid (101955) Bennu by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and SecurityRegolith Explorer) mission, which indicate a surface that is between 100 million and 1 billion years old, predating Bennu’s
expected duration as a near-Earth asteroid. We also observe many fractured boulders, the morphology of which suggests an
influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface.
However, the surface also shows signs of more recent mass movement: clusters of boulders at topographic lows, a deficiency
of small craters and infill of large craters. The oldest features likely record events from Bennu’s time in the main asteroid belt.
Mars exploration has been guided by the search for water. The more complex quest by Mars Science
Laboratory for habitable environments should illuminate the Martian environmental history, and
possibly deliver insights into extraterrestrial life.
Evidence for widespread hydrated minerals on asteroid (101955) BennuSérgio Sacani
Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRISREx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the
form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there
is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the
visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming
previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic
chemistry to Earth.
It has been proposed that ~3.4 billion years ago an ocean fed by enormous catastrophic floods covered
most of the Martian northern lowlands. However, a persistent problem with this hypothesis is the
lack of definitive paleoshoreline features. Here, based on geomorphic and thermal image mapping in
the circum-Chryse and northwestern Arabia Terra regions of the northern plains, in combination with
numerical analyses, we show evidence for two enormous tsunami events possibly triggered by bolide
impacts, resulting in craters ~30km in diameter and occurring perhaps a few million years apart. The
tsunamis produced widespread littoral landforms, including run-up water-ice-rich and bouldery lobes,
which extended tens to hundreds of kilometers over gently sloping plains and boundary cratered
highlands, as well as backwash channels where wave retreat occurred on highland-boundary surfaces.
The ice-rich lobes formed in association with the younger tsunami, showing that their emplacement
took place following a transition into a colder global climatic regime that occurred after the older
tsunami event. We conclude that, on early Mars, tsunamis played a major role in generating and
resurfacing coastal terrains.
Craters, boulders and regolith of (101955) Bennu indicative of an old and dyn...Sérgio Sacani
Small, kilometre-sized near-Earth asteroids are expected to have young and frequently refreshed surfaces for two reasons:
collisional disruptions are frequent in the main asteroid belt where they originate, and thermal or tidal processes act on them
once they become near-Earth asteroids. Here we present early measurements of numerous large candidate impact craters on
near-Earth asteroid (101955) Bennu by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and SecurityRegolith Explorer) mission, which indicate a surface that is between 100 million and 1 billion years old, predating Bennu’s
expected duration as a near-Earth asteroid. We also observe many fractured boulders, the morphology of which suggests an
influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface.
However, the surface also shows signs of more recent mass movement: clusters of boulders at topographic lows, a deficiency
of small craters and infill of large craters. The oldest features likely record events from Bennu’s time in the main asteroid belt.
Mars exploration has been guided by the search for water. The more complex quest by Mars Science
Laboratory for habitable environments should illuminate the Martian environmental history, and
possibly deliver insights into extraterrestrial life.
Evidence for widespread hydrated minerals on asteroid (101955) BennuSérgio Sacani
Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRISREx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the
form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there
is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the
visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming
previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic
chemistry to Earth.
It has been proposed that ~3.4 billion years ago an ocean fed by enormous catastrophic floods covered
most of the Martian northern lowlands. However, a persistent problem with this hypothesis is the
lack of definitive paleoshoreline features. Here, based on geomorphic and thermal image mapping in
the circum-Chryse and northwestern Arabia Terra regions of the northern plains, in combination with
numerical analyses, we show evidence for two enormous tsunami events possibly triggered by bolide
impacts, resulting in craters ~30km in diameter and occurring perhaps a few million years apart. The
tsunamis produced widespread littoral landforms, including run-up water-ice-rich and bouldery lobes,
which extended tens to hundreds of kilometers over gently sloping plains and boundary cratered
highlands, as well as backwash channels where wave retreat occurred on highland-boundary surfaces.
The ice-rich lobes formed in association with the younger tsunami, showing that their emplacement
took place following a transition into a colder global climatic regime that occurred after the older
tsunami event. We conclude that, on early Mars, tsunamis played a major role in generating and
resurfacing coastal terrains.
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.
Hawaii's Most Active Volcano: Here's The Latest On Kilauea's Eruption
The Kilauea volcano is located in the southeastern part of the Big Island of Hawaii.
Believe it or not, Kilauea has been erupting continuously since 1983, with only occasional pauses of quiet activity. This particular "episode" of the eruption began in the late afternoon of May 3, in a part of Leilani Estates, a subdivision near the town of Pahoa.
Officials said there is no way to predict how long the eruption will continue or what shape it will take. This eruption could be finished or could go on for a long time.
Kilauea is one of the most active and well-monitored volcanoes in the world. It's been erupting on and off for hundreds of thousands of years.
All of Hawaii is a tourist destination, but this particular eruption wasn't in an area where most tourists go. The homes at risk are in a subdivision near the town of Pahoa.
Source: USA TODAY. By Doyle Rice. May 4, 2018, accessed May 5, 2018
<https://www.usatoday.com/story/news/nation/2018/05/04/hawaii-volcano-eruption-kilauea-big-island/580466002/>
________________________
Kilauea Volcano Erupts, Spewing Lava and Gases Near Homes in Hawaii
Governor David Ige has issued an emergency proclamation and has called up the National Guard to help emergency workers with evacuation efforts.
Source: THE NEW YORK TIMES. By Meghan Miner Murray, Sabrina Tavernise and Maya Salam. May 4, 2018, accessed May 5, 2018
<https://www.nytimes.com/2018/05/04/us/kilauea-volcano-eruption-hawaii.html>
Modern water at low latitudes on Mars: Potential evidence from dune surfacesSérgio Sacani
Landforms on the Martian surface are critical to understanding the nature of surface processes in the recent
past. However, modern hydroclimatic conditions on Mars remain enigmatic, as explanations for the formation
of observed landforms are ambiguous. We report crusts, cracks, aggregates, and bright polygonal ridges on the
surfaces of hydrated salt-rich dunes of southern Utopia Planitia (~25°N) from in situ exploration by the Zhurong
rover. These surface features were inferred to form after 1.4 to 0.4 million years ago. Wind and CO2 frost processes can be ruled out as potential mechanisms. Instead, involvement of saline water from thawed frost/snow is
the most likely cause. This discovery sheds light on more humid conditions of the modern Martian climate and
provides critical clues to future exploration missions searching for signs of extant life, particularly at low latitudes with comparatively warmer, more amenable surface temperatures.
A large impact crater beneath Hiawatha Glacier in northwest GreenlandSérgio Sacani
We report the discovery of a large impact crater beneath Hiawatha Glacier in northwest Greenland. From airborne radar surveys, we identify a 31-kilometer-wide, circular bedrock depression beneath up to a kilometer of ice. This depression has an elevated rim that cross-cuts tributary subglacial channels and a subdued central uplift that appears to be actively eroding. From ground investigations of the deglaciated foreland, we identify overprinted structures within Precambrian bedrock along the ice margin that strike tangent to the subglacial rim. Glaciofluvial sediment from the largest river draining the crater contains shocked quartz and other impact- related grains. Geochemical analysis of this sediment indicates that the impactor was a fractionated iron aster- oid, which must have been more than a kilometer wide to produce the identified crater. Radiostratigraphy of the ice in the crater shows that the Holocene ice is continuous and conformable, but all deeper and older ice appears to be debris rich or heavily disturbed. The age of this impact crater is presently unknown, but from our geological and geophysical evidence, we conclude that it is unlikely to predate the Pleistocene inception of the Greenland Ice Sheet.
Predictions of the_atmospheric_composition_of_gj_1132_bSérgio Sacani
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly
characterizable small exoplanets currently known. In this paper we study the interaction of a magma
ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more
than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the
amount of O2
that can build up in the atmosphere as a result of hydrogen dissociation and loss.
We find that the magma ocean absorbs at most ∼ 10% of the O2 produced, whereas more than
90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our
simulations is a tenuous atmosphere dominated by O2
, although for very large initial water abundances
atmospheres with several thousands of bars of O2
are possible. A substantial steam envelope would
indicate either the existence of an earlier H2
envelope or low XUV flux over the system’s lifetime. A
steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2
or N2
-rich atmospheres on GJ 1132 b.
Fizzy Super-Earths: Impacts of Magma Composition on the Bulk Density and Stru...Sérgio Sacani
Lava worlds are a potential emerging population of Super-Earths that are on close-in orbits around their host stars,
with likely partially molten mantles. To date, few studies have addressed the impact of magma on the observed
properties of a planet. At ambient conditions, magma is less dense than solid rock; however, it is also more
compressible with increasing pressure. Therefore, it is unclear how large-scale magma oceans affect planet
observables, such as bulk density. We update ExoPlex, a thermodynamically self-consistent planet interior
software, to include anhydrous, hydrous (2.2 wt% H2O), and carbonated magmas (5.2 wt% CO2). We find that
Earth-like planets with magma oceans larger than ∼1.5 R⊕ and ∼3.2 M⊕ are modestly denser than an equivalentmass
solid planet. From our model, three classes of mantle structures emerge for magma ocean planets: (1) a
mantle magma ocean, (2) a surface magma ocean, and (3) one consisting of a surface magma ocean, a solid rock
layer, and a basal magma ocean. The class of planets in which a basal magma ocean is present may sequester
dissolved volatiles on billion-year timescales, in which a 4 M⊕ mass planet can trap more than 130 times the mass
of water than in Earth’s present-day oceans and 1000 times the carbon in the Earth’s surface and crust.
New data from spacecraft currently operating both on the surface
and in orbit are revealing a very rich and complex history of
water on Mars. Morphologic and remote sensing evidence from
Geologic history of water on mars
these missions indicates that volcanic, fluvial, lacustrine, glacial
and aeolian processes have operated throughout Martian geologic
time
A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar f...Sérgio Sacani
The dwarf planets Sedna, Gonggong, and Quaoar are interesting in being somewhat smaller than
the methane-rich bodies of the Kuiper Belt (Pluto, Eris, Makemake), yet large enough to be
spherical and to have possibly undergone interior melting and differentiation. They also reside
on very different orbits, making them an ideal suite of bodies for untangling effects of size and
orbit on present day surface composition. We observed Sedna, Gonggong, and Quaoar with the
NIRSpec instrument on the James Webb Space Telescope (JWST). All three bodies were
observed in the low-resolution prism mode at wavelengths spanning 0.7 to 5.2 μm. Quaoar was
additionally observed at 10x higher spectral resolution from 0.97 to 3.16 μm using mediumresolution gratings. Sedna’s spectrum shows a large number of absorption features due to ethane
(C2H6), as well as acetylene (C2H2), ethylene (C2H4), H2O, and possibly minor CO2.
Gonggong’s spectrum also shows several, but fewer and weaker, ethane features, along with
stronger and cleaner H2O features and CO2 complexed with other molecules. Quaoar’s prism
spectrum shows even fewer and weaker ethane features, the deepest and cleanest H2O features, a
feature at 3.2 μm possibly due to HCN, and CO2 ice. The higher-resolution medium grating
spectrum of Quaoar reveals several overtone and combination bands of ethane and methane
(CH4). Spectra of all three objects show steep red spectral slopes and strong, broad absorptions
between 2.7 and 3.6 μm indicative of complex organic molecules. The suite of light
hydrocarbons and complex organic molecules are interpreted as the products of irradiation of
methane. The differences in apparent abundances of irradiation products among these three
similarly-sized bodies are likely due to their distinctive orbits, which lead to different timescales
of methane retention and to different charged particle irradiation environments. In all cases,
however, the continued presence of light hydrocarbons implies a resupply of methane to the
2
surface. We suggest that these three bodies have undergone internal melting and geochemical
evolution similar to the larger dwarf planets and distinct from all smaller KBOs. The feature
identification presented in this paper is the first step of analysis, and additional insight into the
relative abundances and mixing states of materials on these surfaces will come from future
spectral modeling of these data.
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
Builder.ai Founder Sachin Dev Duggal's Strategic Approach to Create an Innova...Ramesh Iyer
In today's fast-changing business world, Companies that adapt and embrace new ideas often need help to keep up with the competition. However, fostering a culture of innovation takes much work. It takes vision, leadership and willingness to take risks in the right proportion. Sachin Dev Duggal, co-founder of Builder.ai, has perfected the art of this balance, creating a company culture where creativity and growth are nurtured at each stage.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Accelerate your Kubernetes clusters with Varnish CachingThijs Feryn
A presentation about the usage and availability of Varnish on Kubernetes. This talk explores the capabilities of Varnish caching and shows how to use the Varnish Helm chart to deploy it to Kubernetes.
This presentation was delivered at K8SUG Singapore. See https://feryn.eu/presentations/accelerate-your-kubernetes-clusters-with-varnish-caching-k8sug-singapore-28-2024 for more details.
DevOps and Testing slides at DASA ConnectKari Kakkonen
My and Rik Marselis slides at 30.5.2024 DASA Connect conference. We discuss about what is testing, then what is agile testing and finally what is Testing in DevOps. Finally we had lovely workshop with the participants trying to find out different ways to think about quality and testing in different parts of the DevOps infinity loop.
Slack (or Teams) Automation for Bonterra Impact Management (fka Social Soluti...Jeffrey Haguewood
Sidekick Solutions uses Bonterra Impact Management (fka Social Solutions Apricot) and automation solutions to integrate data for business workflows.
We believe integration and automation are essential to user experience and the promise of efficient work through technology. Automation is the critical ingredient to realizing that full vision. We develop integration products and services for Bonterra Case Management software to support the deployment of automations for a variety of use cases.
This video focuses on the notifications, alerts, and approval requests using Slack for Bonterra Impact Management. The solutions covered in this webinar can also be deployed for Microsoft Teams.
Interested in deploying notification automations for Bonterra Impact Management? Contact us at sales@sidekicksolutionsllc.com to discuss next steps.
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
Kubernetes & AI - Beauty and the Beast !?! @KCD Istanbul 2024Tobias Schneck
As AI technology is pushing into IT I was wondering myself, as an “infrastructure container kubernetes guy”, how get this fancy AI technology get managed from an infrastructure operational view? Is it possible to apply our lovely cloud native principals as well? What benefit’s both technologies could bring to each other?
Let me take this questions and provide you a short journey through existing deployment models and use cases for AI software. On practical examples, we discuss what cloud/on-premise strategy we may need for applying it to our own infrastructure to get it to work from an enterprise perspective. I want to give an overview about infrastructure requirements and technologies, what could be beneficial or limiting your AI use cases in an enterprise environment. An interactive Demo will give you some insides, what approaches I got already working for real.
Let's dive deeper into the world of ODC! Ricardo Alves (OutSystems) will join us to tell all about the new Data Fabric. After that, Sezen de Bruijn (OutSystems) will get into the details on how to best design a sturdy architecture within ODC.
"Impact of front-end architecture on development cost", Viktor TurskyiFwdays
I have heard many times that architecture is not important for the front-end. Also, many times I have seen how developers implement features on the front-end just following the standard rules for a framework and think that this is enough to successfully launch the project, and then the project fails. How to prevent this and what approach to choose? I have launched dozens of complex projects and during the talk we will analyze which approaches have worked for me and which have not.
The Art of the Pitch: WordPress Relationships and SalesLaura Byrne
Clients don’t know what they don’t know. What web solutions are right for them? How does WordPress come into the picture? How do you make sure you understand scope and timeline? What do you do if sometime changes?
All these questions and more will be explored as we talk about matching clients’ needs with what your agency offers without pulling teeth or pulling your hair out. Practical tips, and strategies for successful relationship building that leads to closing the deal.
Neuro-symbolic is not enough, we need neuro-*semantic*Frank van Harmelen
Neuro-symbolic (NeSy) AI is on the rise. However, simply machine learning on just any symbolic structure is not sufficient to really harvest the gains of NeSy. These will only be gained when the symbolic structures have an actual semantics. I give an operational definition of semantics as “predictable inference”.
All of this illustrated with link prediction over knowledge graphs, but the argument is general.
LF Energy Webinar: Electrical Grid Modelling and Simulation Through PowSyBl -...DanBrown980551
Do you want to learn how to model and simulate an electrical network from scratch in under an hour?
Then welcome to this PowSyBl workshop, hosted by Rte, the French Transmission System Operator (TSO)!
During the webinar, you will discover the PowSyBl ecosystem as well as handle and study an electrical network through an interactive Python notebook.
PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
- A fully editable and extendable library for grid component modelling;
- Visualization tools to display your network;
- Grid simulation tools, such as power flows, security analyses (with or without remedial actions) and sensitivity analyses;
The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
What you will learn during the webinar:
- For beginners: discover PowSyBl's functionalities through a quick general presentation and the notebook, without needing any expert coding skills;
- For advanced developers: master the skills to efficiently apply PowSyBl functionalities to your real-world scenarios.
Search and Society: Reimagining Information Access for Radical FuturesBhaskar Mitra
The field of Information retrieval (IR) is currently undergoing a transformative shift, at least partly due to the emerging applications of generative AI to information access. In this talk, we will deliberate on the sociotechnical implications of generative AI for information access. We will argue that there is both a critical necessity and an exciting opportunity for the IR community to re-center our research agendas on societal needs while dismantling the artificial separation between the work on fairness, accountability, transparency, and ethics in IR and the rest of IR research. Instead of adopting a reactionary strategy of trying to mitigate potential social harms from emerging technologies, the community should aim to proactively set the research agenda for the kinds of systems we should build inspired by diverse explicitly stated sociotechnical imaginaries. The sociotechnical imaginaries that underpin the design and development of information access technologies needs to be explicitly articulated, and we need to develop theories of change in context of these diverse perspectives. Our guiding future imaginaries must be informed by other academic fields, such as democratic theory and critical theory, and should be co-developed with social science scholars, legal scholars, civil rights and social justice activists, and artists, among others.
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
The publishing industry has been selling digital audiobooks and ebooks for over a decade and has found its groove. What’s changed? What has stayed the same? Where do we go from here? Join a group of leading sales peers from across the industry for a conversation about the lessons learned since the popularization of digital books, best practices, digital book supply chain management, and more.
Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
Transcript: Selling digital books in 2024: Insights from industry leaders - T...
In situ radiometric_and_exposure_age_dating_of_the_martian_surface
1. Research Articles
using the instrument suite aboard the
Curiosity rover exploring Gale crater.
Geologic Setting
Gale is a ~150 km diameter impact
crater that formed near the Late Noachian - Early Hesperian boundary (5,
K. A. Farley,1* C. Malespin,2 P. Mahaffy,2 J. P. Grotzinger,1 P. M.
6), or around 3.7-3.5 Ga according to
Vasconcelos,3 R. E. Milliken,4 M. Malin,5 K. S. Edgett,5 A. A. Pavlov,2 impact crater models (3, 7). In addition
to the ~5 km high central mountain of
J. A. Hurowitz,6 J. A. Grant,7 H. B. Miller,1 R. Arvidson,8 L. Beegle,9
stratified rock informally known as Mt.
9
2
10
2
F. Calef, P. G. Conrad, W. E. Dietrich, J. Eigenbrode, R.
Sharp, the crater is partially filled with
Gellert,11 S. Gupta,12 V. Hamilton,13 D. M. Hassler,13 K.W. Lewis,14 S. sedimentary rocks derived from the
crater rim. Crater density distributions
M. McLennan,6 D. Ming,15 R. Navarro-González,16 S. P.
imply a somewhat younger age (Early
17
18
1
19
Schwenzer, A. Steele, E. M. Stolper, D. Y. Sumner, D.
to Late Hesperian, or ~3.5-2.9 Ga) for
at least some of these deposits (5, 6).
Vaniman,20 A. Vasavada,9 K. Williford,9 R. F. WimmerWhile heading for its destination at Mt.
Schweingruber,21 and the MSL Science Team†
Sharp, Curiosity traversed a gently
1
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125,
sloping plain where local outcrops of
USA. 2NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. 3School of Earth Sciences,
pebble conglomerate were encountered,
4
University of Queensland, Brisbane, Queensland, QLD 4072, Australia. Department of Geological
recording the presence of an ancient
5
Sciences, Brown University, Providence, RI 02912, USA. Malin Space Science Systems, San Diego, CA
stream bed (8). Most of this surface is
6
7
92121, USA. Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, USA. Center
heavily cratered and covered with rock
for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 6th at
and soil (Fig. 1). However, a substantial
Independence SW, Washington, DC 20560, USA. 8Department of Earth and Planetary Sciences,
expanse of bare bedrock was encounWashington University in St. Louis, St. Louis, MO, 63130, USA. 9Jet Propulsion Laboratory, California
Institute of Technology, Pasadena, CA 91109, USA. 10Earth and Planetary Science Department, University
tered in an ~5 m deep topographic
of California, Berkeley, CA 94720, USA. 11Department of Physics, University of Guelph, Guelph, ON N1G
trough (Yellowknife Bay) representing
12
2W1, Canada. Department of Earth Science and Engineering, Imperial College London, London SW7
an erosional window through a se2AZ, UK. 13Southwest Research Institute, Boulder, CO 80302, USA. 14Department of Geosciences,
quence of stratified rocks known as the
15
Princeton University, Princeton, NJ 08544, USA. NASA Johnson Space Center, Houston, TX 77058, USA.
Yellowknife Bay formation (Fig. S1
16
Universidad Nacional Autonoma de Mexico, Coyoacan, Mexico City 4510, Mexico. 17Department of
18
and (9)). These rocks consist mostly of
Physical Sciences, CEPSAR, Walton Hall, Milton Keynes MK7 6AA, UK. Carnegie Institution, Geophysical
distal alluvial fan and lacustrine facies
Laboratory, Washington, DC 20015, USA. 19Department of Geology, University of California, Davis, CA
of basaltic bulk composition and were
95616, USA. 20Planetary Science Institute, Tucson, AZ 85719, USA. 21University of Kiel, Kiel D-24098,
Germany.
derived from the crater rim (9, 10).
Compared to adjacent geological units,
*Corresponding author. E-mail: farley@gps.caltech.edu
the Yellowknife Bay trough is notable
†MSL Science Team authors and affiliations are listed in the supplementary materials.
for its lack of visible craters and its
apparently greater degree of stripping
We determined radiogenic and cosmogenic noble gases in a mudstone on the floor
of impact ejecta and wind-blown soil.
of Gale crater. A K-Ar age of 4.21 ± 0.35 Ga represents a mixture of detrital and
This appearance suggests active eroauthigenic components, and confirms the expected antiquity of rocks comprising
sion, distinctly different from the adjathe crater rim. Cosmic-ray-produced 3He, 21Ne, and 36Ar yield concordant surface
cent map units (9). However, the
exposure ages of 78 ± 30 Ma. Surface exposure occurred mainly in the present
depositional age of the Yellowknife
geomorphic setting rather than during primary erosion and transport. Our
Bay formation, its stratigraphic relaobservations are consistent with mudstone deposition shortly after the Gale impact,
tionship to the adjacent alluvial fan and
or possibly in a later event of rapid erosion and deposition. The mudstone remained
to the strata of Mt. Sharp, and the causburied until recent exposure by wind-driven scarp retreat. Sedimentary rocks
es and timing of its exposure are all
exposed by this mechanism may thus offer the best potential for organic biomarker
presently uncertain.
preservation against destruction by cosmic radiation.
As shown in Fig. 1, the Sheepbed
mudstone and stratigraphically overlying Gillespie Lake sandstone of the
Multiple orbiter and rover missions have documented a rich geologic
Yellowknife Bay formation (9) form a rock couplet of apparently variarecord on the surface of Mars, likely spanning almost the entire history
ble rock hardness, and their contact has eroded to form a decimeter-scale
of the planet (e.g., 1). However, interpretation of this record is impeded
topographic step. The Sheepbed-Gillespie Lake contact is sharp and
by our limited understanding of the connection between the materials
marked by scouring of the underlying mudstone, producing a small scarp
observed and their absolute age. Impact crater densities are the primary
and in some locations an overhang. Calved-off blocks of the sandstone
means for establishing a chronology for geologic features on Mars and
occur at the base and a few meters outboard of the scarp, but not beyond
other solar system bodies (2–4), but crater-based dating methods suffer
(see figure 3 of (9)). This suggests that residual fragments of the degradfrom multiple sources of uncertainty that obscure both absolute and relaing scarp are removed efficiently enough to leave only a very thin lag
tive ages. In contrast, on Earth, isotopic dating methods provide a powdeposit at locations where the Gillespie Lake member is now completely
erful quantitative framework for defining geologic history and for
absent.
identifying the rates and causes of geologic phenomena. Here we report
The distinctive erosional profile of the Sheepbed-Gillespie Lake conresults of an attempt to apply in-situ isotopic dating methods to Mars,
/ http://www.sciencemag.org/content/early/recent / 9 December 2013 / Page 1 / 10.1126/science.1247166
Downloaded from www.sciencemag.org on December 9, 2013
In Situ Radiometric and Exposure Age
Dating of the Martian Surface
2. tact can be traced around the full width of Yellowknife Bay (9) with the
Sheepbed unit making up the floor of the encircled trough. This trough is
elongated in the NE-SW direction, creating an amphitheater-shaped
planimetric form open to the NE. Beyond the Gillespie Lake contact, the
more resistant units higher in the section form similar scarps stepping
upward a total of ~5 m to the uppermost unit of the Yellowknife Bay
formation (Fig. S1). Within the Sheepbed unit, mm- to cm-scale topographic protrusions form fields of small ridges that have been streamlined in the NE-SW direction (Fig. 2). Along with the morphology of the
Yellowknife Bay trough, this observations indicates a dominant role for
SW-directed wind erosion. These observations implicate eolian processes in eroding the mudstone, in efficiently wearing down any blocks that
are delivered to its surface from the encircling scarps or from distal impacts, and in expanding the exposure of the Yellowknife Bay formation.
Scientific investigations at Yellowknife Bay focused on the Sheepbed mudstone. This fine-grained (<50 μm) rock was drilled twice for
mineralogical and evolved gas analyses (11, 12). In addition, multiple
chemical analyses were obtained on outcropping mudstone as well as the
drill tailings. The two drilled samples, referred to as John Klein and
Cumberland, were located ~3 m apart, and yielded very similar results.
The mudstone is composed of detrital and authigenic components consisting of both crystalline and x-ray amorphous phases (11). The detrital
fraction includes minerals typical of volcanic rocks: plagioclase, pyroxenes, and minor olivine, sanidine and ilmenite. Crystalline authigenic
phases include smectitic clay (possibly saponite) and magnetite, thought
to have formed as a result of chemical alteration of detrital olivine, and
minor akaganeite, pyrrhotite, bassanite, and hematite. Quartz and halite
were reported, but very near the CheMin detection limit. Chlorate or
perchlorate was also tentatively identified (12). A model for the amorphous component, comprising about one third of the sample, indicates it
is composed mainly of Si, Fe, Ca, S, and Cl (11). It likely includes poorly crystalline or finely crystalline materials and may include detrital
volcanic and impact-derived glass. The presence of smectite, magnetite,
and akaganeite suggests that the mudstone has not experienced burial
heating above ~200°C, (11, 13). It is possible that the sample experienced no burial heating at all.
Geochronology Overview: K/Ar and Cosmogenic Isotopes
Noble gas isotopes can quantitatively constrain the age and erosion
history of the Sheepbed mudstone. 40Ar from 40K decay will record a
potassium-weighted average of the formation or cooling ages of the
multiple components of the mudstone. 36Ar, 21Ne, and 3He are produced
by irradiation of the uppermost ~2-3 m of the Martian surface by galactic
cosmic rays (GCRs) (14). These cosmogenic isotopes are commonly
used to assess exposure histories of meteorites (e.g., 15, 16) and erosion
rates and styles of terrestrial rocks (e.g., 17). Because the Martian atmosphere is very thin and the magnetic field very weak (18), the Martian
surface is only weakly shielded from GCRs. Thus cosmogenic isotope
production rates are much higher than on Earth (14, 19). The chemistry
of the Sheepbed mudstone (10) is such that the most abundant cosmogenic isotope is likely to be 36Ar produced from the capture of cosmogenic thermal neutrons by Cl, followed by 3He produced by spallation
mainly of O, Si, and Mg, followed by 21Ne from spallation of Mg, Si,
and Al (20). The mudstone’s exposure history is thus recorded by multiple isotopic systems.
The depth-dependence of the production functions of the two spallation isotopes are very similar: a small maximum at ~15 cm below the
surface reflecting development of the nuclear cascade in the uppermost
layers of rock, followed by an exponential decay with an e-folding depth
of ~1 m as the energetic particles attenuate (Fig. 3). In contrast, the production rate of 36Ar from neutron capture has a larger subsurface maximum at greater depth (~60 cm) arising from the combined effects of the
production of neutrons within the descending cascade and the loss of low
energy neutrons into the Martian atmosphere (e.g., 19).
The concentration of a single cosmogenic isotope yields a nonunique exposure history for the rock. The customary end-member interpretive models are to assume either no erosion, in which case a surface
exposure age is obtained, or steady erosion from great depth, in which
case a mean erosion rate is obtained (e.g., 17). Figure 3 shows that this
non-uniqueness can be eliminated by combining spallogenic and neutron
capture isotope measurements. In particular, a rock of Sheepbed composition initially at a depth of greater than a few meters that was instantaneously exposed at the surface would have 36Ar/3He of ~1.5 and
36
Ar/21Ne of ~13. In contrast, if steady erosion causes progressive
downward migration of the surface toward the sample, then the sample
integrates the entire depth profile including the large subsurface 36Ar
peak. Such a rock would have 36Ar/3He~4 and 36Ar/21Ne~30. In both
erosion scenarios the 3He/21Ne ratio is ~8; this isotope pair provides a
cross-check but no additional information on exposure history.
Results and Discussion
Geochronology measurements were performed on the Cumberland
drilled powder (21). After drilling, the sample was sieved and an aliquot
with estimated mass of 135 ± 18 mg (22) was introduced into a quartz
cup in the Sample Analysis at Mars (SAM) instrument. The cup was
moved into position in an oven, sealed against Mars atmosphere, and
evacuated. The sample was then heated to a maximum temperature of
~890°C for 25 min, and the evolved gases were purified and admitted
into the quadrupole mass spectrometer for analysis. All reported measurements used the high sensitivity semi-static analysis mode.
K-Ar Age
The Ar concentration and the APXS-determined K2O concentration
yield a K-Ar age of 4.21 ± 0.35 Ga (1σ) for the Cumberland sample
(Table 1). This age calculation assumes all measured 40Ar is radiogenic
(23). Although a fairly uniform level of excess Ar is thought to be present in some young Martian meteorites (24), that same level of excess
would contribute <0.03 Ga to the age of this high K2O, high Ar concentration rock. One important implication of this very high K-Ar age is that
processing in the SAM oven has extracted essentially all radiogenic 40Ar
despite a fairly low extraction temperature. This surprisingly high yield
(25) may result from rapid diffusive loss from the inherently fine grain
size of the mudstone (probably enhanced by the powdering process of
the drill (26)). Alternatively, the volatile constituents in the mudstone
may promote loss via flux-induced melting. Since fine grain size and
flux-melting will affect the noble gas isotopes similarly, effective extraction of 36Ar, 21Ne and 3He might also be expected. The high age also
implies that a very large fraction of the radiogenic Ar was retained in the
mudstone over geologic time.
The interpretation of the K-Ar age depends critically on where potassium is located in the rock. If a fraction FD of the potassium is in the
detrital phases and the remainder in authigenic phases, then the bulk age
(TB) is a potassium-weighted average of the age of the detritus (TD) and
the age of authigenesis (TA): TB=(1-FD)TA+FDTD. If all of the potassium
is carried in the detrital components (mainly sanidine, plagioclase and
possibly basalt glass), FD=1. In this case the K-Ar system records a mixture of the ages of components present in the crater rim, principally bedrock ranging from minimally to completely reset by the Gale-forming
impact. Crater rim lithologies as well as the crater itself are thought to
range from Noachian to early-Hesperian in age, or about 4.1 to 3.5 Ga
(5, 6, 27–29), in agreement with the K-Ar age of 4.21 ± 0.35 Ga we
measured. Because formation of K-bearing authigenic phases can only
lower the mudstone age below that of the detrital component, we conclude with 95% confidence (30) that the potassium-weighted mean age
of the materials in the Gale crater wall exceeds 3.6 Ga. Alternatively, if
the potassium is entirely hosted within authigenic components (phyllo-
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 2 / 10.1126/science.1247166
3. silicates or amorphous phases other than basalt glass), FD=0 and the age
records the formation age of those phases. In this case 4.21 Ga would
represent a minimum age of mudstone deposition.
At present we have no definitive way to determine the potassium
distribution in the mudstone, but we can make a reasonable estimate. Kbearing phases determined by CheMin include sanidine (1.8%), andesine
feldspar (21%) and an unknown fraction of basaltic or impact glass (11).
CheMin cannot determine the K2O content of any of these phases, so we
assume representative values of 13%, 0.3%, and 1%, respectively (31).
By assuming the mudstone contains 10% glass, we conclude that the
detrital component accounts for 80% of the measured K2O. The remainder could then be in the authigenic clay (18% of the mudstone) with
0.6% K2O, in agreement with K2O concentrations in saponite in a Martian meteorite (32). If we assume TD<4.1 Ga based on crater-count ages
of the Gale impact and host terrains, and use the 95% confidence lower
limit on the K-Ar age of 3.6 Ga, we obtain a current best estimate that
the mudstone was deposited prior to 1.6 Ga. Assuming either a younger
age for the detrital component or a smaller fraction of it in the mudstone
would cause this estimate to rise.
Cosmogenic 36Ar, 21Ne, and 3He
36
Ar, 21Ne, and 3He were all detected at levels that cannot be attributed to sources other than cosmic ray irradiation (33). In the mudstone, 36Ar/3He and 36Ar/21Ne are 1.7 ± 0.5 and 12 ± 5, respectively (34).
These ratios are within error of predictions of the no-erosion scenario
(1.5 and 13) and very different from the prediction of the steady erosion
scenario (4 and 30). Thus we cast our results in terms of surface exposure age, which for 3He, 21Ne, and 36Ar are 72 ± 15, 84 ± 28 and 79 ± 24
Ma, respectively. These ages could be the sum of multiple shorter exposure intervals separated by burial events, e.g., by exposure during initial
deposition and then again by recent re-exposure, or alternatively by burial and exhumation associated with migrating eolian deposits. However,
these events would have to involve rapid burial and removal of at least a
few meters of cover to maintain the good match of measured nuclide
concentration ratios to those of production at the surface.
The agreement among these results argues for complete extraction of
all three noble gases in the SAM oven, and against substantial loss of
noble gases over the ~78 Myr period of cosmic ray exposure. For example, diffusive loss of He from amorphous phases, plagioclase and phyllosilicates might occur at Mars ambient temperature (35), but the 3He/21Ne
ratio of ~7.5 ± 2.6 matches the expected production ratio of ~8. Similarly, dissolution and reprecipitation of a water-soluble Cl-rich phase by
occasional wetting of the mudstone might release accumulated 36Ar. If
this occurred to a significant extent, then the agreement between the 36Ar
exposure age and the 21Ne and 3He exposure ages would have to be fortuitous. While not impossible, we see no evidence for it in these data.
A significant portion of the 3He and 21Ne must be carried by detrital
minerals including plagioclase and pyroxene because these are important
host phases for the major target elements (36). In contrast, the enrichment of Cl compared to a typical Martian basalt suggests much of this
element was added to the mudstone from solution (9, 10). This distinction implies that, while 3He and 21Ne might record cosmic ray irradiation
that occurred during primary exposure and transport in addition to that
acquired during modern exposure at Yellowknife Bay, the same is not
true of 36Ar. The logical interpretation of the good agreement among all
three exposure ages is that all three reflect exposure only in the modern
setting.
The apparent absence of a detrital cosmogenic signal favors deposition of the mudstone in an environment in which erosion and transport
were fairly rapid and/or in which the Martian surface was shielded from
cosmic rays by a reasonably dense atmosphere. The transition from
comparatively wet conditions and a thick atmosphere to cold and dry
conditions with a thin atmosphere is thought to have occurred around the
Noachian-Hesperian boundary (37). Because wet conditions favor rapid
erosion, in either scenario the cosmogenic isotope observations would
support deposition of the Sheepbed mudstone shortly after Gale formation. Alternatively, deposition may have occurred in association with
a later event in which material was eroded and transported rapidly
enough to prevent detectable cosmogenic production. A late erosional
event has also been suggested for Amazonian-age fan formation in some
other Martian craters (38–40).
Topography, stratigraphy and surface exposure dating suggest that
the Yellowknife Bay trough is currently a focus of erosion, and that erosion is occurring by scarp retreat. The Sheepbed mudstone lies below a
sequence of relatively more resistant units that define a series of topographic steps (A-A’ in Fig. S1). The pace of wind erosion for the entire
escarpment will be set by the retreat rate of these more resistant units.
Deflation of the softer units, such as the mudstone, however, undercuts
and contributes to collapse of the resistant layers (Fig. 1), such that both
direct wind abrasion of resistant units and removal of the softer units
contribute to slope retreat. Resistant units and corresponding local steps
will thicken or thin as erosion sweeps into units with variable thicknesses and resistance properties. This predominately lateral erosion has
caused scarp migration to the southwestward and possibly other directions, and produced several meters of surface lowering. The general
flattening of the topographic profile (Fig. S1) as it extends into the Yellowknife Bay trough may indicate that a more resistant unit beneath the
Sheepbed mudstone has slowed continued removal of this unit.
In such a model, the scarp retreat rate can be estimated from the surface exposure ages. To prevent cosmogenic nuclide accumulation requires at least 2-3 m of overburden. Southwestward from the drill site
(and downwind, according to Fig. 3) this amount of overburden is first
encountered about 60 m away (Fig. S1). Thus, in a model in which the
mudstone is rapidly exposed from >2-3 m depth to the surface, the scarp
retreat rate over the last ~80 Ma averages ~0.75 m/Ma. At this rate, the
full extent of the Yellowknife Bay exposure could have been produced
over several hundred million years of steady lateral erosion. Alternatively, wind erosion and associated scarp retreat may be highly episodic,
perhaps in response to climatic variations tied to Mars’ obliquity cycle
(41, 42). Either way, surface exposure ages may vary substantially
around the Yellowknife Bay outcrop and other similar exposures, in
principle offering a test of the scarp retreat hypothesis.
Implications for Organic Preservation
Cosmic rays penetrating the uppermost several meters of rock create
a cascade of atomic and subatomic particles, electrons, and photons that
ionize molecules and atoms in their path (e.g., 43, 44). Complex organic
molecules are particularly susceptible to degradation by such particles,
and because these particles also produce the cosmogenic nuclides, we
have a way to assess the likely magnitude of this degradation in the
Cumberland sample. Degradation of organic molecules in Martian surface rocks subjected to cosmic ray irradiation has been modeled (44).
When scaled to the long-term cosmic ray dose implied by the cosmogenic nuclides in the Cumberland sample, these rates predict reductions of
between 2 and 3 orders of magnitude in the concentration of organic
molecules in the 100-400 AMU range.
The scarp retreat hypothesis offers a possible strategy for minimizing the degree of organic degradation in samples obtained during the
further course of exploration by Curiosity and possible future missions.
Because exposure ages and thus cosmic ray doses should decrease toward a bounding scarp (at least in the downwind direction), such a location may offer the best potential for organic preservation. Given our
estimated scarp retreat rate, locations within a few tens of cm of a fewmeter-scale scarp may have been exposed to cosmic rays for less than a
few Ma. Such a short exposure compares favorably to what can reasonably be expected from alternative sampling strategies relying on recent
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 3 / 10.1126/science.1247166
4. impact craters or drilling to obtain fresh strata.
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Acknowledgments: The authors are indebted to the Mars Science Laboratory
Project engineering and management teams for their exceptionally skilled and
diligent efforts in making the mission as effective as possible and enhancing
science operations. We are also grateful to all those MSL team members who
participated in tactical and strategic operations. Without the support of both
the engineering and science teams, the data presented here could not have
been collected. Three anonymous reviewers provided many helpful
suggestions. Some of this research was carried out at the Jet Propulsion
Laboratory, California Institute of Technology, under a contract with the
National Aeronautics and Space Administration. Data presented in this paper
are archived in the Planetary Data System (pds.nasa.gov).
Supplementary Materials
www.sciencemag.org/cgi/content/1247166/DC1
Materials and Methods
Figs. S1 to S3
Tables S1 to S4
References (48–67)
14 October 2013; accepted 25 November 2013
Published online 09 December 2013
10.1126/science.1247166
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 6 / 10.1126/science.1247166
7. Table 1. Geochronology data.
Sheepbed Mudstone
Cumberland Sample
Sample Mass
K-Ar System
K2O (wt %)
40
Ar (nmol/g)
K-Ar Age (Ga)
0.135 ± 0.018 g
±1σ
0.50
0.08
11.95
1.71
4.21
0.35
Cosmogenic Isotopes
Isotope
3
He
21
Ne
36
Ar
pmol/g
33.7
4.49
55.6
±
6.9
1.52
16.8
PR (pmol g−1 Ma−1)A
Surface
2m Average
0.466
0.254
0.054
0.034
0.714
1.029
Exposure AgeB
(Ma)
±
72
15
84
28
78
24
Notes: elemental composition from APXS measurement of Cumberland drill tailings. AModel isotope production rate (47).
BSurface exposure age assuming no erosion.
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 7 / 10.1126/science.1247166
8. Fig. 1. Mastcam view looking 79° west of North. With increasing distance the Yellowknife Bay formation includes the
Sheepbed mudstone, Gillespie Lake sandstone, and Point Lake outcrop (36 m away). In the distance, the mostly rockand sand-covered Bradbury rise is visible. The large outcrop on the near horizon (marked “x”) is 240 m distant and
stands 13 m above the Gillespie Lake-Sheepbed contact. This is a portion of a 40 frame M-100 mosaic taken on Sol
188 between 13:27 and 13:48 LMST (2013-02-14 23:41:35 and 2013-02-15 00:03:23 PST). The images in the full
mosaic, acquired as sequence mcam01009, have picture IDs between 0188MR0010090000202415I01 and
0188MR0010090390202454I01.
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 8 / 10.1126/science.1247166
9. Fig. 2. Mars Hand Lens Imager (MAHLI) image of brushed,
gray bedrock outcrop of Sheepbed mudstone near the
Cumberland drill hole. Protrusion of nodules (9) results from
eolian scouring of rock surface, creating wind-tails. Preference
for steep faces of wind-tails on NE side suggests long-term
averaged paleowind direction from NE to SW. This is a portion
of MAHLI image 0291MH0001970010103390C00, acquired
on Sol 291. Illumination from the top/upper left.
Fig. 3. Depth dependence of cosmogenic isotope production rates
3
modeled for a rock of Cumberland mudstone chemistry on Mars. He
21
36
and Ne are spallation isotopes, while Ar is produced by capture of
3
21
cosmogenic neutrons. Note the multiplicative factors applied to He and Ne.
3
A mudstone bulk density of 2.6 g/cm was assumed to convert overburden
mass to linear depth.
/ http://www.sciencemag.org/content/early/recent / 13 December 2013 / Page 9 / 10.1126/science.1247166