Voyager 1 has detected changes in energetic particle intensities that suggest it has reached the outer boundary of the heliosphere and entered interstellar space. Measurements show a sudden decrease in particles of solar origin by over 100 times on August 25, 2012, while galactic cosmic rays increased by 9.3% at the same time. This indicates Voyager 1 has reached a region dominated by interstellar plasma rather than heated solar plasma. The spacecraft is now detecting unexpected anisotropies in cosmic rays and temporary increases that may be associated with large solar storms, implying it is still within a transitional region to the local interstellar medium.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
Dark side of_comet_67_p_churyumov_gerasiemnko_in_august_october_2014Sérgio Sacani
Usando o instrumento Microwave Instrument for Rosetta Orbiter (MIRO), os cientistas estão estudando a região polar sul do cometa no final de sua longa estação de inverno. Os dados sugerem que essas regiões frias e escuras abrigam gelo nas suas primeiras dezenas de centímetros abaixo da superfície em quantidades muito maiores do que as encontradas em outras áreas do cometa.
Desde a sua chegada no Cometa 67P/Churyumov-Gerasimenko, a Rosetta tem pesquisado a superfície e o ambiente desse corpo de forma curiosa. Mas por um longo período de tempo, uma porção do núcleo, as regiões frias e escuras ao redor do polo sul do cometa, permaneceram inacessíveis para quase todos os instrumentos a bordo da sonda.
Devido a uma combinação de sua forma em lobo duplo e a inclinação do seu eixo de rotação, o cometa da Rosetta, tem um padrão sazonal muito peculiar durante a sua órbita de 6.5 anos. As estações estão distribuídas de maneira muito assimétrica entre os dois hemisférios, cada um deles compreende parte tanto dos lobos como do pescoço do cometa.
Na maior parte da órbita do cometa, o hemisfério norte experimenta um verão muito longo, durando cerca de 5.5 anos, e o hemisfério sul passa por um longo, frio e escuro inverno. Contudo, poucos meses antes do cometa passar pelo seu periélio, o ponto na sua órbita, mais próximo do Sol, a situação muda, e o hemisfério sul passa por um breve porém quente verão.
Multi-phase volcanic resurfacing at Loki Patera on IoSérgio Sacani
The Jovian moon Io hosts the most powerful persistently active
volcano in the Solar System, Loki Patera1,2. The interior of this
volcanic, caldera-like feature is composed of a warm, dark floor
covering 21,500 square kilometres3 surrounding a much cooler
central ‘island’4. The temperature gradient seen across areas of
the patera indicates a systematic resurfacing process4–9, which
has been seen to occur typically every one to three years since the
1980s5,10. Analysis of past data has indicated that the resurfacing
progressed around the patera in an anti-clockwise direction at a
rate of one to two kilometres per day, and that it is caused either
by episodic eruptions that emplace voluminous lava flows or by a
cyclically overturning lava lake contained within the patera5,8,9,11.
However, spacecraft and telescope observations have been unable to
map the emission from the entire patera floor at sufficient spatial
resolution to establish the physical processes at play. Here we report
temperature and lava cooling age maps of the entire patera floor at
a spatial sampling of about two kilometres, derived from groundbased
interferometric imaging of thermal emission from Loki Patera
obtained on 8 March 2015 ut as the limb of Europa occulted Io.
Our results indicate that Loki Patera is resurfaced by a multi-phase
process in which two waves propagate and converge around the
central island. The different velocities and start times of the waves
indicate a non-uniformity in the lava gas content and/or crust bulk
density across the patera.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
Storm in teacup_a_radio_quiet_quasar_with_radio_emitting_bubblesSérgio Sacani
Artigo descreve descoberta feita com o VLA de uma tempestade nas ondas de rádio em uma galáxia até então calma, o que traz conclusões sobre a evolução das galáxias.
Reconfinement and loss of stability in jets from active galactic nucleiSérgio Sacani
ets powered by active galactic nuclei appear impressively stable compared with their terrestrial and laboratory coun-terparts—they can be traced from their origin to distances exceeding their injection radius by up to a billion times1,2. However, some less energetic jets get disrupted and lose their coherence on the scale of their host galaxy1,3. Quite remark-ably, on the same scale, these jets are expected to become confined by the thermal pressure of the intra-galactic gas2. Motivated by these observations, we have started a system-atic study of active galactic nuclei jets undergoing reconfine-ment via computer simulations. Here, we show that in the case of unmagnetized relativistic jets, the reconfinement is accom-panied by the development of an instability and transition to a turbulent state. During their initial growth, the perturba-tions have a highly organized streamwise-oriented structure, indicating that it is not the Kelvin–Helmholtz instability, the instability which has been the main focus of the jet stability studies so far4,5. Instead, it is closely related to the centrifugal instability6. This instability is likely to be behind the division of active galactic nuclei jets into two morphological types in the Fanaroff–Riley classification7.
Heterogeneous delivery of silicate and metal to the Earth by large planetesimalsSérgio Sacani
After the Moon’s formation, Earth experienced a protracted bombardment by leftover planetesimals. The mass delivered during
this stage of late accretion has been estimated to be approximately 0.5% of Earth’s present mass, based on highly siderophile
element concentrations in the Earth’s mantle and the assumption that all highly siderophile elements delivered by impacts
were retained in the mantle. However, late accretion may have involved mostly large (≥ 1,500 km in diameter)—and therefore
differentiated—projectiles in which highly siderophile elements were sequestered primarily in metallic cores. Here we present
smoothed-particle hydrodynamics impact simulations that show that substantial portions of a large planetesimal’s core may
descend to the Earth’s core or escape accretion entirely. Both outcomes reduce the delivery of highly siderophile elements to
the Earth’s mantle and imply a late accretion mass that may be two to five times greater than previously thought. Further, we
demonstrate that projectile material can be concentrated within localized domains of Earth’s mantle, producing both positive
and negative 182W isotopic anomalies of the order of 10 to 100 ppm. In this scenario, some isotopic anomalies observed in terrestrial
rocks can be explained as products of collisions after Moon formation.
Hydraulic fracturing has been inferred to trigger the majority of injection-induced earthquakes in western Canada, in contrast to the midwestern United States where massive saltwater disposal is the dominant triggering mechanism. A template-based earthquake catalog from a seismically active Canadian shale play, combined with comprehensive injection data during a 4-month interval, shows that earthquakes are tightly clustered in space and time near hydraulic fracturing sites. The largest event [moment magnitude (MW) 3.9] occurred several weeks after injection along a fault that appears to extend from the injection zone into crystalline basement. Patterns of seismicity indicate that stress changes during operations can activate fault slip to an offset distance of >1 km, whereas pressurization by hydraulic fracturing into a fault yields episodic seismicity that can persist for months.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
Dark side of_comet_67_p_churyumov_gerasiemnko_in_august_october_2014Sérgio Sacani
Usando o instrumento Microwave Instrument for Rosetta Orbiter (MIRO), os cientistas estão estudando a região polar sul do cometa no final de sua longa estação de inverno. Os dados sugerem que essas regiões frias e escuras abrigam gelo nas suas primeiras dezenas de centímetros abaixo da superfície em quantidades muito maiores do que as encontradas em outras áreas do cometa.
Desde a sua chegada no Cometa 67P/Churyumov-Gerasimenko, a Rosetta tem pesquisado a superfície e o ambiente desse corpo de forma curiosa. Mas por um longo período de tempo, uma porção do núcleo, as regiões frias e escuras ao redor do polo sul do cometa, permaneceram inacessíveis para quase todos os instrumentos a bordo da sonda.
Devido a uma combinação de sua forma em lobo duplo e a inclinação do seu eixo de rotação, o cometa da Rosetta, tem um padrão sazonal muito peculiar durante a sua órbita de 6.5 anos. As estações estão distribuídas de maneira muito assimétrica entre os dois hemisférios, cada um deles compreende parte tanto dos lobos como do pescoço do cometa.
Na maior parte da órbita do cometa, o hemisfério norte experimenta um verão muito longo, durando cerca de 5.5 anos, e o hemisfério sul passa por um longo, frio e escuro inverno. Contudo, poucos meses antes do cometa passar pelo seu periélio, o ponto na sua órbita, mais próximo do Sol, a situação muda, e o hemisfério sul passa por um breve porém quente verão.
Multi-phase volcanic resurfacing at Loki Patera on IoSérgio Sacani
The Jovian moon Io hosts the most powerful persistently active
volcano in the Solar System, Loki Patera1,2. The interior of this
volcanic, caldera-like feature is composed of a warm, dark floor
covering 21,500 square kilometres3 surrounding a much cooler
central ‘island’4. The temperature gradient seen across areas of
the patera indicates a systematic resurfacing process4–9, which
has been seen to occur typically every one to three years since the
1980s5,10. Analysis of past data has indicated that the resurfacing
progressed around the patera in an anti-clockwise direction at a
rate of one to two kilometres per day, and that it is caused either
by episodic eruptions that emplace voluminous lava flows or by a
cyclically overturning lava lake contained within the patera5,8,9,11.
However, spacecraft and telescope observations have been unable to
map the emission from the entire patera floor at sufficient spatial
resolution to establish the physical processes at play. Here we report
temperature and lava cooling age maps of the entire patera floor at
a spatial sampling of about two kilometres, derived from groundbased
interferometric imaging of thermal emission from Loki Patera
obtained on 8 March 2015 ut as the limb of Europa occulted Io.
Our results indicate that Loki Patera is resurfaced by a multi-phase
process in which two waves propagate and converge around the
central island. The different velocities and start times of the waves
indicate a non-uniformity in the lava gas content and/or crust bulk
density across the patera.
Evidence for the_thermal_sunyaev-zeldovich_effect_associated_with_quasar_feed...Sérgio Sacani
Using a radio-quiet subsample of the Sloan Digital Sky Survey spectroscopic quasar
catalogue, spanning redshifts 0.5–3.5, we derive the mean millimetre and far-infrared
quasar spectral energy distributions (SEDs) via a stacking analysis of Atacama Cosmology
Telescope and Herschel-Spectral and Photometric Imaging REceiver data. We
constrain the form of the far-infrared emission and find 3σ–4σ evidence for the thermal
Sunyaev-Zel’dovich (SZ) effect, characteristic of a hot ionized gas component with
thermal energy (6.2 ± 1.7) × 1060 erg. This amount of thermal energy is greater than
expected assuming only hot gas in virial equilibrium with the dark matter haloes of
(1 − 5) × 1012h
−1M that these systems are expected to occupy, though the highest
quasar mass estimates found in the literature could explain a large fraction of this
energy. Our measurements are consistent with quasars depositing up to (14.5±3.3) τ
−1
8
per cent of their radiative energy into their circumgalactic environment if their typical
period of quasar activity is τ8 × 108 yr. For high quasar host masses, ∼ 1013h
−1M,
this percentage will be reduced. Furthermore, the uncertainty on this percentage is
only statistical and additional systematic uncertainties enter at the 40 per cent level.
The SEDs are dust dominated in all bands and we consider various models for dust
emission. While sufficiently complex dust models can obviate the SZ effect, the SZ
interpretation remains favoured at the 3σ–4σ level for most models.
Storm in teacup_a_radio_quiet_quasar_with_radio_emitting_bubblesSérgio Sacani
Artigo descreve descoberta feita com o VLA de uma tempestade nas ondas de rádio em uma galáxia até então calma, o que traz conclusões sobre a evolução das galáxias.
Reconfinement and loss of stability in jets from active galactic nucleiSérgio Sacani
ets powered by active galactic nuclei appear impressively stable compared with their terrestrial and laboratory coun-terparts—they can be traced from their origin to distances exceeding their injection radius by up to a billion times1,2. However, some less energetic jets get disrupted and lose their coherence on the scale of their host galaxy1,3. Quite remark-ably, on the same scale, these jets are expected to become confined by the thermal pressure of the intra-galactic gas2. Motivated by these observations, we have started a system-atic study of active galactic nuclei jets undergoing reconfine-ment via computer simulations. Here, we show that in the case of unmagnetized relativistic jets, the reconfinement is accom-panied by the development of an instability and transition to a turbulent state. During their initial growth, the perturba-tions have a highly organized streamwise-oriented structure, indicating that it is not the Kelvin–Helmholtz instability, the instability which has been the main focus of the jet stability studies so far4,5. Instead, it is closely related to the centrifugal instability6. This instability is likely to be behind the division of active galactic nuclei jets into two morphological types in the Fanaroff–Riley classification7.
Heterogeneous delivery of silicate and metal to the Earth by large planetesimalsSérgio Sacani
After the Moon’s formation, Earth experienced a protracted bombardment by leftover planetesimals. The mass delivered during
this stage of late accretion has been estimated to be approximately 0.5% of Earth’s present mass, based on highly siderophile
element concentrations in the Earth’s mantle and the assumption that all highly siderophile elements delivered by impacts
were retained in the mantle. However, late accretion may have involved mostly large (≥ 1,500 km in diameter)—and therefore
differentiated—projectiles in which highly siderophile elements were sequestered primarily in metallic cores. Here we present
smoothed-particle hydrodynamics impact simulations that show that substantial portions of a large planetesimal’s core may
descend to the Earth’s core or escape accretion entirely. Both outcomes reduce the delivery of highly siderophile elements to
the Earth’s mantle and imply a late accretion mass that may be two to five times greater than previously thought. Further, we
demonstrate that projectile material can be concentrated within localized domains of Earth’s mantle, producing both positive
and negative 182W isotopic anomalies of the order of 10 to 100 ppm. In this scenario, some isotopic anomalies observed in terrestrial
rocks can be explained as products of collisions after Moon formation.
Hydraulic fracturing has been inferred to trigger the majority of injection-induced earthquakes in western Canada, in contrast to the midwestern United States where massive saltwater disposal is the dominant triggering mechanism. A template-based earthquake catalog from a seismically active Canadian shale play, combined with comprehensive injection data during a 4-month interval, shows that earthquakes are tightly clustered in space and time near hydraulic fracturing sites. The largest event [moment magnitude (MW) 3.9] occurred several weeks after injection along a fault that appears to extend from the injection zone into crystalline basement. Patterns of seismicity indicate that stress changes during operations can activate fault slip to an offset distance of >1 km, whereas pressurization by hydraulic fracturing into a fault yields episodic seismicity that can persist for months.
Bright features have been recently discovered by Dawn on Ceres, which extend
previous photometric and Space Telescope observations. These features should produce
distortions of the line profiles of the reflected solar spectrum and therefore an apparent
radial velocity variation modulated by the rotation of the dwarf planet. Here we report
on two sequences of observations of Ceres performed in the nights of 31 July, 26-
27 August 2015 by means of the high-precision HARPS spectrograph at the 3.6-m
La Silla ESO telescope. The observations revealed a quite complex behaviour which
likely combines a radial velocity modulation due to the rotation with an amplitude of
⇡ ±6 m s
Evidence of a plume on Europa from Galileo magnetic and plasma wave signaturesSérgio Sacani
The icy surface of Jupiter’s moon, Europa, is thought to lie
on top of a global ocean1–4. Signatures in some Hubble Space
Telescope images have been associated with putative water
plumes rising above Europa’s surface5,6, providing support for
the ocean theory. However, all telescopic detections reported
were made at the limit of sensitivity of the data5–7
, thereby calling
for a search for plume signatures in in-situ measurements.
Here, we report in-situ evidence of a plume on Europa from
the magnetic field and plasma wave observations acquired on
Galileo’s closest encounter with the moon. During this flyby,
which dropped below 400 km altitude, the magnetometer8
recorded an approximately 1,000-kilometre-scale field rotation
and a decrease of over 200 nT in field magnitude, and
the Plasma Wave Spectrometer9 registered intense localized
wave emissions indicative of a brief but substantial increase
in plasma density. We show that the location, duration and
variations of the magnetic field and plasma wave measurements
are consistent with the interaction of Jupiter’s corotating
plasma with Europa if a plume with characteristics inferred
from Hubble images were erupting from the region of Europa’s
thermal anomalies. These results provide strong independent
evidence of the presence of plumes at Europa.
O centro da nossa Via Láctea é um lugar misterioso. Não somente está a milhares de anos-luz de distância, mas está também escondido sob grande quantidade de poeira de modo que a maior parte das estrelas em seu interior são invisíveis. Pesquisadores de Harvard, estão propondo uma nova maneira de limpar a neblina e registrar as estrelas ali escondidas. Eles sugerem observar os comprimentos de onda de rádio provenientes das estrelas supersônicas.
“Existem muitas, nós não sabemos sobre o centro galáctico, e nós queremos aprender muito”, disse o principal autor do estudo Idan Ginsburg do Harvard-Smithsonian Center for Astrophysics (CfA). “Usando essa técnica, nós podemos encontrar estrelas que ninguém observou antes”.
A grande trajetória do centro da nossa galáxia para a Terra é repleta de tanta poeira que até mesmo dos trilhões de fótons de luz visível que veem em nossa direção, somente um fóton atingirá nossos telescópios. Ondas de rádio, de uma diferente parte do espectro eletromagnético, possui energia mais baixa e comprimentos de onda maiores. Elas podem passar pela poeira de forma ilesa.
Discrete and broadband electron acceleration in Jupiter’s powerful auroraSérgio Sacani
The most intense auroral emissions from Earth’s polar regions,
called discrete for their sharply defined spatial configurations, are
generated by a process involving coherent acceleration of electrons
by slowly evolving, powerful electric fields directed along the
magnetic field lines that connect Earth’s space environment to its
polar regions1,2. In contrast, Earth’s less intense auroras are generally
caused by wave scattering of magnetically trapped populations of
hot electrons (in the case of diffuse aurora) or by the turbulent or
stochastic downward acceleration of electrons along magnetic field
lines by waves during transitory periods (in the case of broadband
or Alfvénic aurora)3,4. Jupiter’s relatively steady main aurora has a
power density that is so much larger than Earth’s that it has been
taken for granted that it must be generated primarily by the discrete
auroral process5–7. However, preliminary in situ measurements of
Jupiter’s auroral regions yielded no evidence of such a process8–10.
Here we report observations of distinct, high-energy, downward,
discrete electron acceleration in Jupiter’s auroral polar regions. We
also infer upward magnetic-field-aligned electric potentials of up to
400 kiloelectronvolts, an order of magnitude larger than the largest
potentials observed at Earth11. Despite the magnitude of these
upward electric potentials and the expectations from observations
at Earth, the downward energy flux from discrete acceleration is less
at Jupiter than that caused by broadband or stochastic processes,
with broadband and stochastic characteristics that are substantially
different from those at Earth.
Resolved imaging confirms a radiation belt around an ultracool dwarfSérgio Sacani
Radiation belts are present in all large-scale Solar System planetary
30 magnetospheres: Earth, Jupiter, Saturn, Uranus, and Neptune1. These persistent
31 equatorial zones of relativistic particles up to tens of MeV in energy can extend farther
32 than 10 times the planet’s radius, emit gradually varying radio emissions2–4 and impact
33 the surface chemistry of close-in moons5. Recent observations demonstrate that very low
34 mass stars and brown dwarfs, collectively known as ultracool dwarfs, can produce planet35
like radio emissions such as periodically bursting aurorae6–8 from large-scale
36 magnetospheric currents9–11. They also exhibit slowly varying quiescent radio
37 emissions7,12,13 hypothesized to trace low-level coronal flaring14,15 despite departing from
38 empirical multi-wavelength flare relationships8,15. Here we present high resolution
39 imaging of the ultracool dwarf LSR J1835+3259 at 8.4 GHz demonstrating that its
40 quiescent radio emission is spatially resolved and traces a double-lobed and axisymmetric
41 structure similar in morphology to the Jovian radiation belts. Up to 18 ultracool dwarf
42 radii separate the two lobes, which are stably present in three observations spanning
43 more than one year. For plasma confined by the magnetic dipole of LSR J1835+3259, we
44 estimate 15 MeV electron energies consistent with Jupiter’s radiation belts4. Our results
45 confirm recent predictions of radiation belts at both ends of the stellar mass sequence8,16–
46 19 and support broader re-examination of rotating magnetic dipoles in producing non47
thermal quiescent radio emissions from brown dwarfs7, fully convective M dwarfs20, and
4
Different Martian Crustal Seismic Velocities across the Dichotomy Boundary fr...Sérgio Sacani
Article This article is protected by copyright. All rights reserved.
Abstract
We have observed both minor-arc (R1) and major-arc (R2) Rayleigh waves for the largest marsquake (magnitude
of 4.7 ± 0.2) ever recorded. Along the R1 path (in the lowlands), inversion results show that a simple, two-layer
model with an interface located at 21 - 29 km and an upper crustal shear-wave velocity of 3.05 - 3.17 km/s can fit the
group velocity measurements. Along the R2 path, observations can be explained by upper crustal thickness models
constrained from gravity data and upper crustal shear-wave velocities of 2.61 - 3.27 km/s and 3.28 - 3.52 km/s in the
lowlands and highlands, respectively. The shear-wave velocity being faster in the highlands than in the lowlands
indicates the possible existence of sedimentary rocks, and relatively higher porosity in the lowlands.
Lunar ejecta origin of near-Earth asteroid Kamo’oalewa is compatible with rar...Sérgio Sacani
Near-Earth asteroid, Kamo’oalewa (469219), is one of a small number of known quasisatellites of Earth; it transitions between quasi-satellite and horseshoe orbital states on
centennial timescales, maintaining this dynamics over megayears. The similarity of its
reflectance spectrum to lunar silicates and its Earth-like orbit both suggest that it originated
from the lunar surface. Here we carry out numerical simulations of the dynamical evolution of
particles launched from different locations on the lunar surface with a range of ejection
velocities in order to assess the hypothesis that Kamo‘oalewa originated as a debris-fragment
from a meteoroidal impact with the lunar surface. As these ejecta escape the Earth-Moon
environment, they face a dynamical barrier for entry into Earth’s co-orbital space. However, a
small fraction of launch conditions yields outcomes that are compatible with Kamo‘oalewa’s
orbit. The most favored conditions are launch velocities slightly above the escape velocity
from the trailing lunar hemisphere.
The mass of_the_mars_sized_exoplanet_kepler_138_b_from_transit_timingSérgio Sacani
Artigo da revista Nature, descreve o trabalho de astrônomos para medir o tamanho e a massa de um exoplaneta parecido com Marte, além de caracterizar por completo o sistema planetário da estrela Kepler-138.
Similar to Search for the_exit_voyager1_at_heliosphere_border_with_the_galaxy (20)
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
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sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
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Search for the_exit_voyager1_at_heliosphere_border_with_the_galaxy
1. Reports
/ http://www.sciencemag.org/content/early/recent / 27 June 2013 / Page 1/ 10.1126/science.1235721
Humankind’s quest for exploration of the neighborhood of our solar
system is currently embodied in the Voyager 1 (V1) and 2 (V2) space-
craft launched over 35 years ago, and currently at distances of 123 and
101 AU (1 AU = 1.5 × 108
km) from the Sun, and at heliographic lati-
tudes of 34.5° and – 30.2°, respectively. Ideas about the dimensions and
shape of the bubble of plasma called the heliosphere, created by the con-
tinuously flowing solar wind as the Sun travels through the LISM, are
older than the space age (1). We present data from Voyager 1 showing
that the intensities of energetic particles populating the hot heliosheath,
i.e., the region between the solar wind termination shock [TS (2)] and
the expected outer boundary, the heliopause (HP) have suddenly de-
creased to instrumental background while galactic cosmic rays (GCR)
have simultaneously increased to levels thought to be characteristic of
the LISM (3).
V1 data used herein are from the Low Energy Charged Particle
(LECP) instrument that measures differential intensities of ions 40 keV
to ~ 60 MeV nuc−1
and of electrons 26 keV to > 10 MeV together with
an integral ion measurement > 211MeV, determines the composition of
ions > 200 keV nuc−1
, and provides angular information via a mechani-
cally stepped platform (4). Ion angular data provide estimates of plasma
flow velocities at V1 (2) (fig. S1) in the absence of direct measurements
from the V1 Plasma Science instrument (that failed in 1980). Data from
other instruments on V1 are discussed in accompanying reports (5, 6).
The HP is expected to be a tangential discontinuity that separates the
solar wind plasma from plasma in the LISM. Models of the interface
take into account the solar wind and LISM plasma and neutral (H atoms)
components, the interstellar and heliospheric magnetic fields, galactic
and anomalous cosmic rays (ACR), as well as latitudinal and solar cycle
variations of the solar wind [(7, 8) and references therein]. The V1 and
V2 spacecraft are the only space missions able to provide quantitative, in
situ, measurements that can test predictions of the various models.
LECP observations since 2004 have delineated the properties of the
TS (2, 9), detected the cessation of radial expansion of the solar wind
within the HS at ~ 113 AU (10) marking the beginning of a transition
region, while establishing that there was no statistically significant me-
ridional flow at distances > 119 AU (11) at V1. The latter two observa-
tions have been interpreted differently
in different models (12–14). Plasma
flow has been mostly azimuthal averag-
ing ~ -26 km s−1
(11), i. e. in the direc-
tion opposite that of planetary motion.
Subsequent LECP measurements on V1
over the past several months have re-
vealed unexpected spatial/temporal
structures that are the subject of this
report.
Figure 1A shows large, several per-
cent changes in GCR intensity of both
short (a few days) and long (few
months) duration in hourly- averaged
intensities since mid-2012. The overall
increase from 2012.365 (May 7) to the
beginning of 2013 is ~ 30%. If the
structures are stationary, V1 traveling at
~ 0.01 AU d−1
traverses 0.05 AU in 5
days, i.e., comparable to the gyroradius
of a 1 GeV GCR (0.1 AU) in a 0.4 nT
magnetic field (6) and may be inter-
preted as spatial variations. The data in
Fig. 1B demonstrate, however, that near
simultaneous, order of magnitude, de-
creases occurred within a single day in
low energy ions with gyroradii of only
~3x10−4
AU, i.e., comparable to the distance traversed by V1 in an hour.
Electrons with a gyroradius ~ 10−5
AU correspond to a V1 travel time of
only a few minutes. We note, however, that electron intensities began a
slow decay months before at the first onset of an increase in GCR on
May 7, dropped precipitously on day 210 together with the ions, recov-
ered briefly but then disappeared before the 2nd
partial decrease on day
222. We address the nature of the sharp “edge” to the hot heliosheath on
day 238 and its relationship to the two “precursor” features by examin-
ing the intensity anisotropies measured by LECP.
Figure 2A shows that the two partial depletions of ~ 4 MeV protons
depended on the direction of motion of the particles with respect to the
local magnetic field. As shown in the pie plots, particles gyrating per-
pendicular to the magnetic field were depleted least, whereas those mov-
ing parallel to the field were depleted most, with a deeper depletion on
d231 than on d212. During the subsequent flux recovery between d233
and d236, the fluxes were still anisotropic but with a clear-cut one-sided
loss cone distribution, indicating that protons were streaming as previ-
ously (11) in the azimuthal (-T) direction (S3), but were now only weak-
ly returning in the +T direction along field lines beyond the spacecraft.
The fluxes in the final ion decrease on d238 are highly anisotropic with
the intensity of protons streaming along the –T direction dropping first
(S3), whereas those gyrating perpendicular to the magnetic field (S1, S5)
decrease much more slowly. This “mirroring“ distribution is maintained
for over 50 days to 2012.71.
Figure 2B establishes that, despite the bi-directional response of our
>211 MeV proton channel, there must be significant anisotropies in
GCRs throughout most of the period plotted. These anisotropies are
particularly strong after the final GCR increase on d238. Inspection of
the pie plots show that GCRs were roughly isotropic in mid-2012, but
became gradually anisotropic during the brief spikes in intensity, and
durably so after the final increase on 2012.63 (d238). GCRs return to
near-isotropy on 2012.88, but the anisotropy reappears on 2012.96 and
increases thereafter. The presence of any anisotropy in GCRs, other than
the well-known but small Compton-Getting anisotropy (15) observed
when V1 was within the fast-flowing solar wind inside the TS, is in itself
an unexpected finding. Long-held views on GCR acceleration and
Search for the Exit: Voyager 1 at
Heliosphere’s Border with the Galaxy
S. M. Krimigis,1,2
* R. B. Decker,1
E. C. Roelof,1
M. E. Hill,1
T. P. Armstrong,3
G.
Gloeckler,4
D. C. Hamilton,5
L. J. Lanzerotti6
1
Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723, USA. 2
Office for Space
Research and Technology, Academy of Athens, 106 79 Athens, Greece. 3
Fundamental Technologies LLC,
Lawrence, KS 66046, USA. 4
University of Michigan, Ann Arbor, MI 48109, USA. 5
University of Maryland,
College Park, MD 20742, USA. 6
New Jersey Institute of Technology, Newark, NJ 07102, USA.
*Corresponding author. E-mail: tom.krimigis@jhuapl.edu
We report measurements of energetic (>40 keV) charged particles on Voyager 1 (V1)
from the interface region between the heliosheath (HS), dominated by heated solar
plasma, and the local interstellar medium (LISM) expected to contain cold non-solar
plasma and the galactic magnetic field. Particles of solar origin at V1, located at 18.5
billion km (123 AU) from the Sun, decreased by a factor >103
on August 25, 2012,
while those of galactic origin (cosmic rays) increased by 9.3% at the same time.
Intensity changes appeared first for particles moving in the azimuthal direction and
were followed by those moving in the radial and antiradial directions with respect to
the solar radius vector. This unexpected heliospheric «depletion region» may form
part of the interface between solar plasma and the galaxy.
onJune27,2013www.sciencemag.orgDownloadedfrom
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transport (16) incorporate steady isotropy in the LISM as a basic as-
sumption, so the observed (time-dependent) GCR anisotropy implies that
V1 is still in a region of transition to the LISM.
We call attention to a clear transient increase in the >211 MeV pro-
ton intensity during ~2013.22-2013.26 (DOY 080-095) that is apparent
in both Figs. 1A and 2B. We suggest that this disturbance in the GCR
intensities at 123.6 AU might be associated with a large global merged
interaction region (GMIR) generated by the extraordinary solar activity
beginning 05 March 2012 that contained 3 X-class and 19 M-class X-ray
flares during the month from active regions near N15-N20 degrees heli-
olatitude (VGR1 is at N34). The average velocity of the GMIR would
have had to be ~120 AU/yr=570 km/s at some location along the field
lines containing the GCRs sampled by VGR1 (but not necessarily at the
spacecraft itself because a non-local enhancement of the GCRs would
propagate rapidly along the field lines).
To quantify the depletion of heliospheric particles and the enhance-
ment of GCRs we examined the energy spectra of the particle popula-
tions (H, He, C, O) before and after the step-like increases/decreases at
the “edge” on day 238 (Fig. 3). We selected the 52-day period 2012.43-
2012.57, before the first short-term depletion as characteristic of the
spectrum prior to the onset of the abrupt changes in intensities. The “af-
ter” period 2012.86-2013.0 begins following the ~ 4 Mev proton return
to relative isotropy on 2012.72 shown in Fig. 2A. The populations of H,
He, and O contain particles of both heliospheric origin and ACRs at
energies <50 MeV nuc−1
. By contrast, C is a minor ACR component but
is comparably abundant to O in GCR at energies ≥ 20 MeV nuc−1
.
The “before” spectra are power laws in energy E of the form ~ E−1.5
and steepen at higher energies, as were measured previously for many
years (2, 16), and as were predicted (17). The “after” spectra are remark-
ably flat over this energy range for the three major ACR species, H, He,
O. The flat O spectrum resembles that observed similar intensities by the
Ulysses spacecraft at high (> 55°) ecliptic latitudes (18) at 1.7 AU and
3.4 AU, suggesting that LISM field lines have direct connection to the
high latitude heliosphere allowing GCR O direct access, much like solar
particles have access to earth’s polar caps. At lower (≤ 1 MeV nuc−1
)
energies there is a near-complete absence of fluxes, with upper limits
shown (Fig. 3) for H, He, and O, all being lower than the “before” inten-
sities by factors > 4x103
for H, He and O and > 30 for C is. At higher
energies, H and He are down by varying factors, and O is lower for E ≤
20 MeV nuc−1
but unchanged above that energy. The C spectrum shows
a small increase at E ≥ 20 MeV nuc−1
, as expected from the primary
GCRs.
The LECP observations presented here, taken by themselves, present
a compelling case that V1 has crossed into a new region of space that
could be labeled “heliospheric depletion”, where hot HS particles are
undetectable at energies > 40 keV. If the predicted location of the puta-
tive HP at 121 AU deduced by combining energetic neutral atom (ENA)
observations and V1 in situ spectra (10) is interpreted as the hot plasma
edge, it extends the depletion down to energies ~5 keV. This view is
supported by the observation that the increase in magnetic field pressure
(6) by a factor of ~ 8 during the two partial depletions was accompanied
by a decrease of only a factor of ~ 2 in the hot particle (>40 keV) pres-
sure (cf. Fig. 1), suggesting that-most of the plasma pressure resides at
energies < 40 keV.
In this region ACRs, thought to be accelerated in the termination
shock and/or its vicinity (19–21), are effectively absent, while GCRs
have ready access and have increased to the highest level ever observed,
presumably representative of intensities (3, 22) not modulated by helio-
spheric magnetic fields. The “emptying” of the hot heliosheath ions de-
duced from the LECP angular distributions, began with magnetic (6)
field-aligned flows in the azimuthal direction. This characteristic of a
loss-cone distribution is observed for particles quasi-trapped in planetary
magnetic fields but with little return flow at small pitch angles implying
an incomplete mirroring configuration. Particles gyrating perpendicular
to the magnetic field also escaped the hot heliosheath, but at a slower
rate. GCRs on the other hand flowed into the HS preferentially along the
magnetic field, increasing to the highest intensity ever observed beyond
the edge.
The main question is how the vicinity of the edge encountered by V1
differs from characteristics expected for the LISM. Some models have
suggested an increase in magnetic field (23), while others predicted only
a gradual drop inthe ACRs and a gradual increase in GCRs (24). No
model predicted either the extreme sharpness of the edge (in all particle
species and the magnetic field) or the discontinuities in these quantities
preceding the edge crossing. The invariance of the magnetic field direc-
tion across the edge during the crossing on day 238 (6) was totally unex-
pected. We suggest in Fig. 4 plasma processes (25) in the vicinity of the
edge that are consistent with these observations. A key element is that
for the year preceding the crossing (2011.6-2012.6) the average radial
plasma flow in the HS fluctuated between positive and negative values
(fig. S1) (11, 26), but was mostly negative (-20 km/s <Vr<+10 km/s), as
determined from anisotropies of > 40 keV ions. The curvature of the
boundary is concave inward, so the Maxwell stresses tend to pull flux
tubes just outside the edge into the heliosheath. But the hot ion pressure
inside the HS is decreasing toward the edge, creating an outward body
force on the plasma that resists the entry of the cold flux tubes.
Consequently, the system may be susceptible to an interchange in-
stability (25), thus allowing the cold, high magnetic field flux tubes to
enter the HS. The most favorable situation for instability is if the tangen-
tial direction of the magnetic field is the same on both sides of the
boundary, in agreement with the magnetic field observations (6). How-
ever, the effect of flows across the boundary are not usually considered
in the classical interchange instabilities. For flux tubes already inside the
HS but near the edge, the mainly negative radial flow will tend to keep
them from crossing the edge. Because of the same mainly negative fluc-
tuations, a LISM flux tube with strong magnetic field and containing
only GCRs and cold interstellar plasma that becomes embedded into the
edge of the hot HS by the instability will tend to move deeper within the
HS. It will then begin to be populated with hot ions, first at 90° pitch
angles (d238) then at all others (d234, cf. Fig. 2A). At the same time, the
GCRs will slowly leak out the flux tube into the HS, thus decreasing
their intensity (Fig. 2B). All the while, the magnetic field intensity will
keep most of its outside value (B0) in order to maintain pressure balance.
The two “precursors” before the edge thus may be the signatures of such
invasive flux tubes from beyond the edge. We then suggest that the rea-
son for the location (and the sharpness) of the edge itself is that the con-
ditions favoring this modified flux-tube interchange process must be
very sensitive to the ratio of the hot ion pressure (P, decreasing outward)
and the magnetic pressure (B2
/2μ0, increasing outward), while their sum
is constrained by pressure balance to the value B0
2
/2μ0 (magnetic pres-
sure beyond the edge).
References and Notes
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Acknowledgments: This work was supported at The Johns Hopkins University
Applied Physics Laboratory (APL) by NASA contract NNN06AA01C, and by
subcontracts at the University of Maryland (UMD) and Fundamental
Technologies, LLC. We are grateful to Jack Gunther and Larry Brown of APL
and Scott Lasley of UMD for assistance in the data analyses efforts.
Supplementary Materials
www.sciencemag.org/cgi/content/full/science.1235721/DC1
Fig. S1
28 January 2013; accepted 4 June 2013
Published online 27 June 2013
10.1126/science.1235721
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Fig. 1. Overview of energetic particle observations at V1, 2012.35-2013.04, showing the contrary behavior of GCRs and
lower-energy particles. (A) Hourly averages of galactic cosmic ray (GCR) activity and the pronounced boundary crossing on
August 25, 2012 (d238). GCR error bars are ±1σ. (B) Intensities of low to medium energy ions and low energy electrons. The
time evolution is very different, depending on energy and species.
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Fig. 2. Anisotropy measurements in ACRs and GCRs. (A) Time evolution of the anisotropy before, during, and after the
boundary crossing are shown. The pie plots represent angular distributions in the LECP scan plane, illustrated by the
pinwheel diagram. The lightly shaded sector -4 is shielded (4) so measurements at low energies are not available. In the RTN
coordinate system R is the radius vector from the Sun, T is cross product of the solar rotation vector with R, and N completes
a right-handed system. The red vector at each pie plot represents the direction of the magnetic field as measured by the
onboard magnetometer (6). (B) Evidence of the anisotropy in GCRs revealed by the LECP measurements, using the
bidirectional telescope (4). The lightly shaded sectors 4 and 8 are not plotted at present due to complications with spacecraft
mechanical obscuration (4). As seen by the pie plots there is a difference between intensities parallel (azimuthal) and
transverse (gyrating) to the measured magnetic field, especially after V1 crossed the “edge” on 2012.64.
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Fig. 3. Spectral evolution across the boundary. Fifty-two-day averaged energy spectra of heliosheath ions and lower
energy ACRs before (dotted lines, open symbols), and after (solid lines, filled symbols) the boundary crossing on 2012.64.
Vertical error bars are statistical errors (often smaller than the symbol) and horizontal bars indicate the energy band over
which the fluxes are determined. The spectra of H, He, C, and O (red circles, blue squares, green triangles, and black
diamond, respectively) outside the boundary are remarkably flat in the LECP energy range, and remarkably consistent with
high latitude measurements from Ulysses in 1994 (18). See text.
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Fig. 4. Schematic summary of salient observations and their possible explanation near the “edge” (see text). The
illustration is drawn in the heliographic R-N plane, so the measured magnetic field direction (which does not change across
the edge) is approximately perpendicular to the page. The “hot heliosheath” (HH) is in pressure balance (P) from hot ions plus
magnetic field (B
2
/2μ0 where μ0=4πx10
−7
) with the “cold heliosheath” (CH) with plasma density N0>N. Beyond the edge the
CH is dominated by magnetic pressure (B0
2
/2μ0) and is devoid of hot ions but contains higher intensities (J0) of galactic
cosmic rays (GCRs). We expect the “cold dense” plasma density N0 in the CH to be near the interstellar value. The inward
radial Maxwell stress (due to draping of CH field lines around the HH) and the inward particle pressure gradient in the HH
(because of the reduction in hot ion intensities) suggest the possibility of a displacement instability at the edge that could
allow flux tubes from the CH to invade the HH where they would commence filling with hot ions while losing their GCRs
(J<J0). The fluctuating radial flows (-20 km/s<Vr<10 km/s) are negative (on average) in the HH (11) (fig. S1), so this will tend
to draw invading flux tubes deeper into the HH, while suppressing the crossing of HH flux tubes across the edge.
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