Daily Archives: 16 Mar 2021

Astronomy

New Footprints From the Gaia-sausage-enceladus Merger Event (Cosmology / Astronomy)

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Looking up at the starry sky, the deep Universe appears quiet and mysterious. It is hard to imagine that the ancient dwarf galaxy Enceladus violently collided and was torn apart by our own Milky Way Galaxy, leaving behind the cries of a whole new generation of children from the hundred-handed giant.

Recently, SCIENCE CHINA: Physics, Mechanics & Astronomy published an (Editor’s Focus) article titled “Low-α Metal-rich stars with sausage kinematics in the LAMOST survey: Are they from the Gaia-Sausage-Enceladus Galaxy?” co-authored by Gang Zhao and Yuqin Chen, researchers from the National Astronomical Observatories, Chinese Academy of Sciences. The article depicts the tortuous process of how the Gaia-Sausage-Enceladus (GSE) dwarf galaxy mysteriously disappeared in a major merger event that occurred long ago in the early history of the Milky Way, and tells the story of how the authors search for their member stars via a multipath exploration method. Simultaneously, two commentaries by Prof. Yipeng Jing from Shanghai Jiao Tong University and Prof. Zhanwen Han from Yunnan Observatory were published.

Dances with wolves—The Accretion of the GSE by the Milky Way

In the cosmic family, there are massive galaxies such as the Milky Way and Andromeda galaxy, but more numerous are dwarf galaxy members such as Sagittarius, the Magellanic Clouds, and GSE. In its long evolutionary history, the Milky Way has been constantly interacting, colliding, and eventually merging with nearby dwarf galaxies, leading to the formation of many substructures. In 2018, the European Space Agency’s Gaia satellite detected the so-called ‘Gaia-Sausage’ structure in velocity space, which is the debris of the GSE dwarf galaxy after ‘dancing’ with the Milky Way. Numerical simulations have revealed that the GSE dwarf galaxy collided head-on with the Milky Way and was buried deep within the Galactic Center 10 billion years ago. The strong impact force in the biggest splash ‘heated’ disk stars up to the Galactic halo, above 4 kpc from the Galactic plane. This is the largest merger event in the Milky Way’s ancient history. This discovery is a milestone in the research field of galaxy formation and evolution.

Being towards Death- GSE Merger Brings New Vitality into the Galaxy

After the GSE dwarf galaxy fell into the Milky Way, this family was completely dissolved, and it is hard to find its member stars in space. In search for these missing member stars, Prof. Gang Zhao proposed a multi-path exploration on the GSE debris based on the LAMOST survey, which opened up a new path to find the merging imprints in velocity space, orbital space, and chemical space by combining forces of two large spectral and astrometric surveys. Based on LAMOST and Gaia data, he and his colleague picked out possible GSE member stars in velocity space. Then they adopted chemical abundances as a DNA test for membership identification, since chemical composition does not vary with stellar positions or motions. In total, they identified 1534 low-α metal-rich member stars of GSE among the 8 million stars from the LAMOST data. This is the first discovery of a low-α metal-rich component of the GSE galaxy. This newly discovered component naturally extends from the previously detected metal-poor component.

Comparison of [Fe/H] and [α/Fe] between DDPayne-LAMOST DR5 and APOGEE DR16 for the three samples (LGB, RC and UGB). Red dash lines are the one-to-one relations and solid lines are calibrations derived from linear fits to the data. Credit: Science China Press

They calculated spatial distributions and estimated the ages of these member stars. Surprisingly, the stars are young, but reach to 4 kpc above the Galactic plane. Since the GSE merger event happened 10 billion years ago, when these member stars were not even born, it is impossible that the “splash” process could bring disk stars to such high positions. This caused doubt on the previous picture of the GSE merging process. Zhao and Chen suggested that these low-α metal-rich member stars had not undergone the splash process but were newly formed from the metal-rich gas of the GSE merger during subsequent evolution. This suggestion is consistent with the hydro-dynamical simulation by Amarante et al. that produces bimodal disk chemistry. Observationally, this work proves that the GSE dwarf galaxy is a clumpy Milky-Way-like analog, which updates our understanding of the chemical evolution of the GSE galaxy.

The GSE merger even is essential to the evolution of the Milky Way. It not only brought in GSE member stars with a different chemical composition, but also changed the distribution of stars in the Milky Way. What’s more, it brought metal-rich gas and triggered new star formation, radiating new vitality in the Milky Way.

Promising Future—Joining Hands to Build the Milky Way Home and March toward the Andromeda Galaxy

In order to verify the bimodal disk chemistry of the GSE galaxy, the authors studied the distribution in orbital space for GSE metal-rich member stars sharing the same velocity but different chemistry. It is found that both high-α and low-α metal-rich stars exhibit the same clumps and strips, which suggests that they are all accreted from GSE and respond to the Galactic gravitational potential in the same way. Interestingly, the dense strip at Zmax=3-5 kpc forms a clear disk-halo transition at 4 kpc from the Galactic plane.

How did the GSE merger form this transition? This is due to the observational effect caused by the unique speed of the GSE member stars under the influence of the gravitational potential of the Milky Way. Since GSE members have nearly zero rotation and their vertical velocities at Zmax (the highest point in their orbits) are also zero, they spend a longer time at Zmax than at other positions (non-zero velocity), leading to a pile-up of stars at |Z|~ 4 kpc. It’s just like cars on the highway. When you’re stuck in a traffic jam, the speed is very low, and you can see a lot of cars clustered together, while few cars are shown at a given place where the speed is high. As a large number of GSE member stars have Zmax=3-5 kpc, we observe a high-density region at |Z|~4kpc. Since their radial velocities are neither zero nor identical, what we see is not a clump, but a long strip.

Why can’t this disk-halo transition be caused by other dwarf galaxies? The transition depends on not only the velocity characteristics and mass of the dwarf galaxy, but also the mass of the Milky Way and the time when the merger event happened. Because the GSE rotates at zero speed and collides head-on with the Milky Way, as well as continuously responds to the Milky Way’s gravitational potential, its member stars show this unique orbital feature. Other dwarf galaxies probably produced clumps elsewhere. For example, the Sagittarius dwarf galaxy merged with the Milky Way at a lower inclination, and their member stars clustered at the apogee of their orbits at about 30 kpc, which is considered to be the transition between the inner and outer halo of the Milky Way. Since other dwarf galaxies do not have the orbital characteristics of the GSE and do not contribute to the |Z|=4 kpc transition, we conclude that it is an imprint left only by the GSE merger event.

For decades 4 kpc has been adopted as the disk-halo transition without knowing the reason of its formation. This is the first time to reveal the physical mechanism by which the GSE merger event causes the apparent separation of the Galactic halo and disk at 4 kpc. It is a true portrayal of the hundred-handed giant’s (GSE’s) children working together to build our Milky Way home.

Over time, the descendants of the GSE and the Galactic inhabitants merged and became indistinguishable in position, kinematic, and chemical space. Under the attraction of gravity, they march toward the distant Andromeda galaxy. According to the latest numerical simulation, our future generations will be able to witness the spectacular collision of the two large galaxies up close and personal in 4 billion years. Eventually, our Milky Way and Andromeda will merge together to become a new galaxy, but our solar system is expected to survive in this merger event.

The future 2-meter China Space Station Telescope (CSST) has great advantages in the systematic search for imprints left by the GSE and in the study of interactions between the Milky Way and Andromeda galaxy. If you’re interested in more stories of galaxy collisions and mergers, stay tuned for further revelations by the CSST project in the future.

Featured image: Gaia-Sausage structure detected by the Gaia satellite in velocity space. Credit: V. Belokurov et al. 2018, MNRAS, 478, 611

Reference: Gang Zhao et al, Low-α metal-rich stars with sausage kinematics in the LAMOST survey: Are they from the Gaia-Sausage-Enceladus galaxy?, Science China Physics, Mechanics & Astronomy (2021). DOI: 10.1007/s11433-020-1645-5

Provided by Science China Press

Astronomy

Ancient Light Illuminates Matter That Fuels Galaxy Formation (Astronomy / Cosmology)

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Using light from the Big Bang, an international team led by Cornell and the U.S. Department of Energy’s Lawrence Berkeley National Laboratory has begun to unveil the material which fuels galaxy formation.

“There is uncertainty on the formation of stars within galaxies that theoretical models are unable to predict,” said lead author Stefania Amodeo, a Cornell postdoctoral researcher in astronomy in the College of Arts and Sciences (A&S), who now conducts research at the Observatory of Strasbourg, France. “With this work, we are providing tests for galaxy formation models to comprehend galaxy and star formation.”

The research, “Atacama Cosmology Telescope: Modeling the Gas Thermodynamics in BOSS CMASS galaxies from Kinematic and Thermal Sunyaev-Zel’dovich Measurements,” appears in the March 15 edition of Physical Review D.

Proto galaxies are always full of gas and when they cool, the galaxies start to form, said senior author Nick Battaglia, assistant professor of astronomy in A&S. “If we were to just do a back-of-the-envelope calculation, gas should turn into stars,” he said. “But it doesn’t.”

Galaxies are inefficient when they manufacture stars, Battaglia said. “About 10% of the gas – at most – in any given galaxy gets turned into stars,” he explained, “and we want to know why.”

The scientists can now check their longtime theoretical work and simulations, by looking at microwave observations with data and applying a 1970s-era mathematical equation. They’ve looked at data from Atacama Cosmology Telescope (ACT) – which observes the Big Bang’s static-filled cosmic microwave background (CMB) radiation – and search for the Sunyaev-Zel’dovich effects. That combination of data enables the scientists to map out the material around that indicate the formation of galaxies in various stages.

“How do galaxies form and evolve in our universe?” Battaglia said. “Given the nature of astronomy, we can’t sit and watch a galaxy evolve. We use various telescopic snapshots of galaxies – and each has its own evolution – and we try and stitch that information together. From there, we can extrapolate Milky Way formation.”

Effectively, the scientists are using the cosmic microwave background – remnants of the Big Bang – as a backlit screen that is 14 billion years old to find this material around galaxies.

“It’s like a watermark on a bank note,” said co-author Emmanuel Schaan, the Chamberlain postdoctoral fellow at the Lawrence Berkeley National Laboratory. “If you put it in front of a backlight then the watermark appears as a shadow. For us, the backlight is the cosmic microwave background. It serves to illuminate the gas from behind, so we can see the shadow as the CMB light travels through that gas.”

Together with Simone Ferraro, divisional fellow at Lawrence Berkeley, Schaan led the measurement part of the project.

“We’re making these measurements of this galactic material at distances from galaxy centers never before done,” Battaglia said. “These new observations are pushing the field.”

In addition to Battaglia, Amodeo, Cornell researchers include doctoral students Emily Moser, Victoria Calafut, Eve Vavagiakis; Steve K. Choi, National Science Foundation postdoctoral fellow at the Cornell Center for Astrophysics and Planetary Astronomy;  Rachel Bean, professor of astronomy and senior associate dean in A&S; and Mike Niemack, associate professor of physics and astronomy in A&S.

The ACT team is an international collaboration, with scientists from 41 institutions in seven countries.

In addition to the National Science Foundation’s Atacama Cosmology Telescope, the work was supported by the Baryon Oscillation Spectroscopic Survey in New Mexico, where the Berkeley Lab played a leading role; the European Space Agency’s Planck telescope and the Herschel Space Telescope; and the Cori supercomputer at Berkeley Lab’s National Energy Research Scientific Computing Center.

A National Science Foundation Astronomy and Astrophysics research grant funded the research.

Reference: Stefania Amodeo et al., “Atacama Cosmology Telescope: Modeling the gas thermodynamics in BOSS CMASS galaxies from kinematic and thermal Sunyaev-Zel’dovich measurements”, Phys. Rev. D 103, 063514 – Published 15 March 2021. https://journals.aps.org/prd/abstract/10.1103/PhysRevD.103.063514

Provided by Cornell University

Medicine

Combination Therapy May Provide Significant Protection Against Lethal Influenza (Medicine)

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Targeting a receptor involved in exaggerated immune response to influenza infection improves survival in animal models, investigators report in The American Journal of Pathology

A significant proportion of hospitalized patients with influenza develop complications of acute respiratory distress syndrome, driven by virus-induced cytopathic effects as well as exaggerated host immune response. Reporting in The American Journal of Pathology, published by Elsevier, investigators have found that treatment with an immune receptor blocker in combination with an antiviral agent markedly improves survival of mice infected with lethal influenza and reduces lung pathology in swine-influenza–infected piglets. Their research also provides insights into the optimal timing of treatment to prevent acute lung injury.

Previously, the investigators found that an excessive influx of neutrophils, infection fighting immune cells, and the networks they create to kill pathogens, known as neutrophil extracellular traps (NETs), contribute to acute lung injury in influenza infection. Formation of NETs by activated neutrophils occurs via a cell death mechanism called NETosis and the released NETs contain chromatin fibers that harbor toxic components.

A mouse model, commonly used in exploring influenza pathophysiology and drug therapies, was used in the current study. Because mice are not natural hosts for influenza, further validation in larger animals is necessary before testing in humans. Therefore, researchers also tested piglets infected with swine influenza virus. The animals were treated with a combination of a CXCR2 antagonist, SCH527123, together with an antiviral agent, oseltamivir.

The combination of SCH527123 and oseltamivir significantly improved survival in mice compared to either of the drugs administered alone. The combination therapy also reduced pulmonary pathology in piglets.

“Combination therapy reduces lung inflammation, alveolitis, and vascular pathology, indicating that aberrant neutrophil activation and release in NETs exacerbate pulmonary pathology in severe influenza,” explains lead investigator Narasaraju Teluguakula, PhD, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, USA. “These findings support the evidence that antagonizing CXCR2 may alleviate lung pathology and may have significant synergistic effects with antiviral treatment to reduce influenza-associated morbidity and mortality.”

It can be challenging to balance the suppression of excessive neutrophil influx without compromising the beneficial host immunity conferred by neutrophils. Therefore, the researchers examined the temporal dynamics of NETs release in correlation with pathological changes during the course of infection in mice. During the early inflammatory phase, three to five days post infection, significant neutrophil activation and NETs release with relatively few hemorrhagic lesions was observed. In the late hemorrhagic exudative phase, significant vascular injury with declining neutrophil activity was seen.

Dr. Teluguakula also emphasizes that these findings provide the first evidence to support the strategy of testing combination therapy in a large animal influenza model. “In view of the close similarities in pulmonary pathology and immune responses between swine and humans, pig-influenza pneumonia models can serve as a common platform in understanding pathophysiology and host-directed drug therapies in human influenza infections and may be useful in advancing the translational impact of drug treatment studies in human influenza infections.”

Notes for editors
The article is “Administration of a CXC Chemokine Receptor 2 (CXCR2) Antagonist, SCH527123, Together with Oseltamivir Suppresses NETosis and Protects Mice from Lethal Influenza and Piglets from Swine-Influenza Infection,” by Harshini K. Ashar, Sivasami Pulavendran,Jennifer M. Rudd, Prasanthi Maram, Mallika Achanta, Vincent T.K. Chow, Jerry R. Malayer, Timothy A. Snider,and Narasaraju Teluguakula (https://doi.org/10.1016/j.ajpath.2020.12.013). It appears online in advance of The American Journal of Pathology, volume 191, issue 4 (April 2021) published by Elsevier.

This work was supported by the National Institute of General Medical Sciences of the NIH under award number P20GM103648; an Oklahoma Center for the Advancement of Science and Technology grant; and a Center for Veterinary Health Sciences, Oklahoma State University grant.

Featured image: Lung pathologic changes and bronchoalveolar lavage inflammatory cellular signatures during the course of lethal-influenza infection. These findings provide important clues regarding the inflammatory cellular signature at different time intervals during severe influenza infection. Temporal dynamics in hematoxylin and eosin–stained lung sections or modified Geimsa–stained bronchoalveolar lavage cells from control and lethal influenza–challenged mice were evaluated at 1, 3, 5, 6, and 8 dpi. Initial epithelial cytopathic effects were prominently seen at 1 dpi (open arrow), which spread to alveoli and were followed by the severe inflammatory phase (3-5 dpi). By 6 dpi, significant vascular leakage and collapse of the alveoli became prominent, and animals died between 8-9 dpi with severe hemorrhagic exudates (hash) with abundant proteinaceous material in the alveolar spaces (asterisk). CON-Control; DPI-Days post infection; M-macrophage; L-lymphocyte; N-neutrophil, EP-epithelial cell. Representative image was selected from 5 mice per group. (Credit: The American Journal of Pathology).

Provided by Elsevier

Planetary Science

IMAGE RELEASE: Cosmic Lens Reveals Faint Radio Galaxy (Planetary Science)

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Radio telescopes are the world’s most sensitive radio receivers, capable of finding extremely faint wisps of radio emission coming from objects at the farthest reaches of the universe. Recently, a team of astronomers used the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) to take advantage of a helping hand from nature to detect a distant galaxy that likely is the faintest radio-emitting object yet found.

The discovery was part of the VLA Frontier Fields Legacy Survey, led by NRAO Astronomer Eric Murphy, which used distant clusters of galaxies as natural lenses to study objects even farther away. The clusters served as gravitational lenses, using the gravitational pull of the galaxies in the clusters to bend and magnify light and radio waves coming from the more-distant objects.

In this composite, a VLA radio image is superimposed on a visible-light image from the Hubble Space Telescope. The prominent red-orange objects are radio relics — large structures possibly caused by shock waves — inside the foreground galaxy cluster, called MACSJ0717.5+3745, which is more than 5 billion light-years from Earth.

The distant galaxy VLAHFF-J071736.66+374506.4, more than 8 billion light-years from Earth.
Credit: Heywood et al.; Sophia Dagnello, NRAO/AUI/NSF; STScI.

Detailed VLA observations showed that many of the galaxies in this image are emitting radio waves in addition to visible light. The VLA data revealed that one of these galaxies, shown in the pullout, is more than 8 billion light-years distant. Its light and radio waves have been bent by the intervening cluster’s gravitational-lensing effect.

The radio image of this distant galaxy, called VLAHFF-J071736.66+374506.4, has been magnified more than 6 times by the gravitational lens, the astronomers said. That magnification is what allowed the VLA to detect it.

“This probably is the faintest radio-emitting object ever detected,” said Ian Heywood, of Oxford University in the UK. “This is exactly why we want to use these galaxy clusters as powerful cosmic lenses to learn more about the objects behind them.”

“The magnification provided by the gravitational lens, combined with extremely sensitive VLA imaging, gave us an unprecedented look at the structure of a galaxy 300 times less massive than our Milky Way at a time when the universe was less than half its current age. This is giving us valuable insights on star formation in such low-mass galaxies at that time and how they eventually assembled into more massive galaxies,” said Eric Jimenez-Andrade, of NRAO.

The scientists are reporting their work in a pair of papers in the Astrophysical Journal.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Featured image: VLA radio image superimposed on a Hubble Space Telescope image of the galaxy cluster MACSJ0717.5+3745. Pullout shows distant galaxy VLAHFF-J071736.66+374506.4, far beyond the cluster, and likely the faintest radio-emitting object ever detected. The cluster is more than 5 billion light-years from Earth; the background galaxy more than 8 billion light-years distant.
Credit: Heywood et al.; Sophia Dagnello, NRAO/AUI/NSF; STScI.

Links to Scientific Papers

(1) Heywood, et al., “The VLA Frontier Fields Survey: Deep, High-resolution Radio Imaging of the MACS Lensing Clusters at 3 and 6 GHz”, ArXiv, pp. 1-29, 2021. https://arxiv.org/abs/2103.07806 (2) Jimenez-Andrade, et al., “The VLA Frontier Field Survey: A Comparison of the Radio and UV/optical size of 0.3≲z≲3 star-forming galaxies”, ArXiv, pp. 1-30, 2021. https://arxiv.org/abs/2103.07807

Provided by NRAO

Medicine

Exposure to Common Chemical Preservative During Pregnancy May Reduce Protection Against Breast Cancer (Medicine)

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UMass Amherst research suggests propylparaben is an endocrine disruptor

Low doses of propylparaben – a chemical preservative found in food, drugs and cosmetics – can alter pregnancy-related changes in the breast in ways that may lessen the protection against breast cancer that pregnancy hormones normally convey, according to University of Massachusetts Amherst research.

The findings, published March 16 in the journal Endocrinology, suggest that propylparaben is an endocrine-disrupting chemical that interferes with the actions of hormones, says environmental health scientist Laura Vandenberg, the study’s senior author. Endocrine disruptors can affect organs sensitive to hormones, including the mammary gland in the breast that produces milk.

Laura Vandenberg © UMass Amherst

“We found that propylparaben disrupts the mammary gland of mice at exposure levels that have previously been considered safe based on results from industry-sponsored studies. We also saw effects of propylparaben after doses many times lower, which are more reflective of human intake,” Vandenberg says. “Although our study did not evaluate breast cancer risk, these changes in the mammary tissue are involved in mitigating cancer risk in women.”

Hormones produced during pregnancy not only allow breast tissue to produce milk for the infant, but also are partly responsible for a reduced risk of breast cancer in women who give birth at a younger age.

The researchers, including co-lead author Joshua Mogus, a Ph.D. student in Vandenberg’s lab,tested whether propylparaben exposure during the vulnerable period of pregnancy and breastfeeding adversely alters the reorganization of the mammary gland. They examined the mothers’ mammary glands five weeks after they exposed the female mice to environmentally doses of propylparaben during pregnancy and breastfeeding.

Compared with pregnant mice that had not received propylparaben, the exposed mice had mammary gland changes not typical of pregnancy, the researchers report. These mice had increased rates of cell proliferation, which Vandenberg says is a possible risk factor for breast cancer. They also had less-dense epithelial structures, fewer immune cell types and thinner periductal collagen, the connective tissue in the mammary gland.

“Some of these changes may be consistent with a loss of the protective effects that are typically associated with pregnancy,” says Mogus, who was chosen to present the research, deemed “particularly newsworthy” by the Endocrine Society, at the international group’s virtual annual meeting, ENDO 2021, beginning March 20.

Joshua Mogus

Mogus says future studies should address whether pregnant females exposed to propylparaben are actually more susceptible to breast cancer. “Because pregnant women are exposed to propylparaben in many personal care products and foods, it is possible that they are at risk,” Mogus says, adding that pregnant and breastfeeding women should try to avoid using products containing propylparaben and other parabens.

“This chemical is so widely used, it may be impossible to avoid entirely,” Mogus adds. “It is critical that relevant public health agencies address endocrine-disrupting chemicals as a matter of policy.”

This research received funding from the University of Massachusetts Commonwealth Honors College Grant, the Endocrine Society’s Summer Research Fellowship and the National Institutes of Health.

Other study co-authors are Charlotte LaPlante, Ruby Bansal, Klara Matouskova, Shannon Silva, Elizabeth Daniele, Mary Hagen and Karen Dunphy, all of UMass Amherst; Benjamin Schneider and Sallie Schneider of Baystate Medical Center in Springfield, Mass.; and D. Joseph Jerry of UMass Amherst’s Department of Veterinary and Animal Sciences and Pioneer Valley Life Sciences Institute in Springfield.

Featured image: Senior author Laura Vandenberg is an associate professor in the UMass Amherst School of Public Health and Health Sciences. © UMass Amherst

Reference: Joshua P Mogus, Charlotte D LaPlante, Ruby Bansal, Klara Matouskova, Benjamin R Schneider, Elizabeth Daniele, Shannon J Silva, Mary J Hagen, Karen A Dunphy, D Joseph Jerry, Sallie S Schneider, Laura N Vandenberg, Exposure to propylparaben during pregnancy and lactation induces long-term alterations to the mammary gland in mice, Endocrinology, 2021;, bqab041, https://doi.org/10.1210/endocr/bqab041

Provided by UMass Amherst

Planetary Science

What Happened to Mars’s Water? It is Still Trapped There (Planetary Science)

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New data challenges the long-held theory that all of Mars’s water escaped into space

Billions of years ago, the Red Planet was far more blue; according to evidence still found on the surface, abundant water flowed across Mars and forming pools, lakes, and deep oceans. The question, then, is where did all that water go?

The answer: nowhere. According to new research from Caltech and JPL, a significant portion of Mars’s water–between 30 and 99 percent–is trapped within minerals in the planet’s crust. The research challenges the current theory that the Red Planet’s water escaped into space.

The Caltech/JPL team found that around four billion years ago, Mars was home to enough water to have covered the whole planet in an ocean about 100 to 1,500 meters deep; a volume roughly equivalent to half of Earth’s Atlantic Ocean. But, by a billion years later, the planet was as dry as it is today. Previously, scientists seeking to explain what happened to the flowing water on Mars had suggested that it escaped into space, victim of Mars’s low gravity. Though some water did indeed leave Mars this way, it now appears that such an escape cannot account for most of the water loss.

“Atmospheric escape doesn’t fully explain the data that we have for how much water actually once existed on Mars,” says Caltech PhD candidate Eva Scheller (MS ’20), lead author of a paper on the research that was published by the journal Science on March 16 and presented the same day at the Lunar and Planetary Science Conference (LPSC). Scheller’s co-authors are Bethany Ehlmann, professor of planetary science and associate director for the Keck Institute for Space Studies; Yuk Yung, professor of planetary science and JPL senior research scientist; Caltech graduate student Danica Adams; and Renyu Hu, JPL research scientist. Caltech manages JPL for NASA.

The team studied the quantity of water on Mars over time in all its forms (vapor, liquid, and ice) and the chemical composition of the planet’s current atmosphere and crust through the analysis of meteorites as well as using data provided by Mars rovers and orbiters, looking in particular at the ratio of deuterium to hydrogen (D/H).

Water is made up of hydrogen and oxygen: H2O. Not all hydrogen atoms are created equal, however. There are two stable isotopes of hydrogen. The vast majority of hydrogen atoms have just one proton within the atomic nucleus, while a tiny fraction (about 0.02 percent) exist as deuterium, or so-called “heavy” hydrogen, which has a proton and a neutron in the nucleus.

The lighter-weight hydrogen (also known as protium) has an easier time escaping the planet’s gravity into space than its heavier counterpart. Because of this, the escape of a planet’s water via the upper atmosphere would leave a telltale signature on the ratio of deuterium to hydrogen in the planet’s atmosphere: there would be an outsized portion of deuterium left behind.

However, the loss of water solely through the atmosphere cannot explain both the observed deuterium to hydrogen signal in the Martian atmosphere and large amounts of water in the past. Instead, the study proposes that a combination of two mechanisms–the trapping of water in minerals in the planet’s crust and the loss of water to the atmosphere–can explain the observed deuterium-to-hydrogen signal within the Martian atmosphere.

When water interacts with rock, chemical weathering forms clays and other hydrous minerals that contain water as part of their mineral structure. This process occurs on Earth as well as on Mars. Because Earth is tectonically active, old crust continually melts into the mantle and forms new crust at plate boundaries, recycling water and other molecules back into the atmosphere through volcanism. Mars, however, is mostly tectonically inactive, and so the “drying” of the surface, once it occurs, is permanent.

“Atmospheric escape clearly had a role in water loss, but findings from the last decade of Mars missions have pointed to the fact that there was this huge reservoir of ancient hydrated minerals whose formation certainly decreased water availability over time,” says Ehlmann.

“All of this water was sequestered fairly early on, and then never cycled back out,” Scheller says. The research, which relied on data from meteorites, telescopes, satellite observations, and samples analyzed by rovers on Mars, illustrates the importance of having multiple ways of probing the Red Planet, she says.

Ehlmann, Hu, and Yung previously collaborated on research that seeks to understand the habitability of Mars by tracing the history of carbon, since carbon dioxide is the principal constituent of the atmosphere. Next, the team plans to continue to use isotopic and mineral composition data to determine the fate of nitrogen and sulfur-bearing minerals. In addition, Scheller plans to continue examining the processes by which Mars’s surface water was lost to the crust using laboratory experiments that simulate Martian weathering processes, as well as through observations of ancient crust by the Perseverance rover. Scheller and Ehlmann will also aid in Mars 2020 operations to collect rock samples for return to Earth that will allow the researchers and their colleagues to test these hypotheses about the drivers of climate change on Mars.

The paper, titled “Long-term Drying of Mars Caused by Sequestration of Ocean-scale Volumes of Water in the Crust,” published in Science on 16 March 2021. This work was supported by a NASA Habitable Worlds award, a NASA Earth and Space Science Fellowship (NESSF) award, and a NASA Future Investigator in NASA Earth and Space Science and Technology (FINESST) award.

Reference: E. L. Scheller, B. L. Ehlmann, Renyu Hu, D. J. Adams, Y. L. Yung, “Long-term drying of Mars by sequestration of ocean-scale volumes of water in the Crust”, Science  16 Mar 2021:
eabc7717 DOI: 10.1126/science.abc7717

Provided by Caltech

Planetary Science

Is There Life on Mars Today – and Where? (Planetary Science)

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In a comment published today in Nature Astronomy, Dr. Nathalie Cabrol, Director of the Carl Sagan Center for Research at the SETI Institute, challenges assumptions about the possibility of modern life on Mars held by many in the scientific community.

As the Perseverance rover embarks on a journey to seek signs of ancient life in the 3.7 billion years old Jezero crater, Cabrol theorizes that not only life could still be present on Mars today, but it could also be much more widespread and accessible than previously believed. Her conclusions are based on years of exploration of early Mars analogs in extreme environments in the Chilean altiplano and the Andes funded by the NASA Astrobiology Institute. It’s essential, she argues, that we consider microbial habitability on Mars through the lens of a 4-billion-year-old environmental continuum rather than through frozen environmental snapshots as we tend to do. Also critical is to remember that, by all terrestrial standards, Mars became an extreme environment very early.

In extreme environments, while water is an essential condition, it is far from being enough. What matters most, Cabrol says, it’s how extreme environmental factors such as a thin atmosphere, UV radiation, salinity, aridity, temperature fluctuations and many more interact with each other, not only water. “You can walk on the same landscape for miles and find nothing. Then, maybe because the slope changes by a fraction of a degree, the texture or the mineralogy of the soil is different because there is more protection from UV, all of a sudden, life is here. What matters in extreme worlds to find life is to understand the patterns resulting from these interactions”. Follow the water is good. Follow the patterns is better.            

This interaction unlocks life’s distribution and abundance in those landscapes. That does not necessarily make it easier to find, as the last refuges for microbes in extreme environments can be at the micro- to nanoscale within the cracks in crystals. On the other hand, observations made in terrestrial analogs suggest that these interactions considerably expand the potential territory for modern life on Mars and could bring it closer to the surface than long theorized.

If Mars still harbors life today, which Cabrol thinks it does, to find it we must take the approach of Mars as a biosphere. As such, its microbial habitat distribution and abundance are tightly connected not only to where life could theoretically survive today but also where it was able to disperse and adapt over the entire history of the planet, and the keys to that dispersion lie in early geological times. Before the Noachian/Hesperian transition, 3.7-3.5 billion years ago, rivers, oceans, wind, dust storms would have taken it everywhere across the planet. “Importantly, dispersal mechanisms still exist today, and they connect the deep interior to the subsurface,” Cabrol says.

But a biosphere cannot run without an engine. Cabrol proposes that the engine to sustain modern life on Mars still exists, that it is over 4 billion years old and migrated out of sight today, underground.

If this correct, these observations may modify our definition of what we call “Special Regions” to include the interaction of extreme environmental factors as a critical element, one that potentially expands their distribution in substantial ways and could have us rethink how to approach them. The issue, here, says Cabrol, is that we do not yet have the global environmental data at a scale and resolution that matters to understand modern microbial habitability on Mars. As human exploration gives us a deadline to retrieve pristine samples, Cabrol suggests options regarding the search for extant life, including the type of missions that could fulfill objectives critical to astrobiology, human exploration, and planetary protection.

The work reported here was supported by the NASA Astrobiology Institute via Grant No. NNA15BB01A.

Featured image: Mars Biosphere Engine. a, The zonally-averaged Mars elevation from MOLA8 shows how the formation of the planetary crustal dichotomy has driven hydrology and energy flux throughout geological times, creating both conditions for an origin of life, the formation of habitats, and dispersal pathways. While conditions do not allow sustained surface water in the present day, recent volcanic activity and subsurface water reservoirs may maintain habitats and dispersal pathways for an extant biosphere. The origin(s) of methane emissions remain enigmatic, their spatial distribution overlapping with areas of magma and water/ice accumulations at the highland/lowlands boundary. b, Young volcanoes in Coprates Chasma, Valles Marineris estimated to be 200-400 million years old by Brož et al. (2017). Credit Image: NASA-JPL/MRO-University of Arizona. c, Regions of subglacial water (blue) detected at the base of the south polar layered deposits by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument. Credit Image: Lauro et al., (2020). 

Reference: Cabrol, N.A. Tracing a modern biosphere on Mars. Nat Astron 5, 210–212 (2021). https://doi.org/10.1038/s41550-021-01327-x DOI: 10.1038/s41550-021-01327-x Read the article here.

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Founded in 1984, the SETI Institute is a non-profit, multi-disciplinary research and education organization whose mission is to explore, understand, and explain the origin and nature of life in the universe and the evolution of intelligence. Our research encompasses the physical and biological sciences and leverages expertise in data analytics, machine learning and advanced signal detection technologies. The SETI Institute is a distinguished research partner for industry, academia and government agencies, including NASA and NSF.

PHYSICS

The Irresistible Pull of Gravity (Physics)

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It is well known that gravity attracts and after reading the essay “The irresistible attraction of gravity” by astrophysicist Luciano Rezzolla – published by Rizzoli and selected as a finalist for the Cosmos Prize – it will also be clear why. Like it or not, we cannot escape gravity and its irresistible pull on our mind, so let us be carried away by the author on a long journey to explore the wonders of the universe.

Whether from the edge of an underground abyss or from the edge of a rock jump on the top of a mountain, from the highest rung of a ladder or from the window of a building, when we look out and look down we inevitably feel attracted. In fact, what attracts us is gravity . It attracts us not only with the body but also with the mind… in the sense that gravity is attractive, both instinctively and rationally.

Just a few seconds after birth, the Moro reflex reveals an important truth of our interaction with gravity: we know it instinctively, well before having conscious interactions with the rest of the physical universe. Then, over time, our knowledge of gravity changes as we develop the ability to observe the physical universe and understand its laws.

There is a person who knows these laws very well, even when they apply to the most extreme objects in the universe. A person who several times, in recent years, has guided us in the understanding of the most fascinating phenomena of nature , and who with patience and clarity has told us what happens in places where our imagination struggles to reach . It is Luciano Rezzolla , astrophysicist of Goethe University in Frankfurt , author of a recent essay – The irresistible attraction of gravity , published by Rizzoli and selected as a finalist for the Cosmos Prize – of which today we propose a review (with some spoilers ).

Cover of the book “The irresistible attraction of gravity: a journey to discover black holes” by Luciano Rezzolla, published by Rizzoli © INAF

From the early years of school, to explain gravity to children we start from the famous Newton’s apple and the fact that – detached from the branch – it does not float in space but falls to the ground. Already in the first chapters of this book you will discover, retracing the work of the fathers of gravity wisely narrated by the author, that this view is limited and even misleading, that gravity is not a force and that mass, alone, is not sufficient to describe it. The author recounts, in a compelling way, the astronomical observations that contributed to opening cracks in Newton’s theory of gravitation, leading the reader to discover – thanks to Einstein’s theory of general relativity – what gravity really is.

You will be joined by the author on a long journey in which, in addition to patience, the effort to imagine a reality very far from the one you are used to is required. On the way you will hardly be left behind, although the physics described are challenging. The author is able to explain in a simple but rigorous way the more complicated aspects of physics, making even the less experienced reader understand how the laws that govern it work. The text is extremely fluent, accurate, full of references to everyday life, of analogies, of comparisons that keep – like gravity – grounded. You will understand the concept of spacetimeand of curvature, you will understand how gravity is nothing more than a manifestation of the latter and that the reason why the apple falls downwards, once detached from the tree, is linked to the sign of the curvature of spacetime in which it is located the tree.

Every now and then you will be called to do mental experiments – Gedankenexperiment , in German – which do not require any instrumental apparatus but only a good dose of imagination and an excellent knowledge of physics. You will have to think about the first, the author will think about the second. These experiments, conducted using only the mind, based on logical and physical considerations, will allow you to obtain “virtual” results that are very difficult, if not impossible, to obtain in the laboratory and will allow you to investigate the limits of gravity.

Understanding the nature of gravity – and how it is inextricably linked to the curvature of spacetime – you will face the other stages of the journey, exploring the limits of gravity itself. Also in this case, the author retraces the historical steps that led – in the late 1950s, early 1960s – to the discovery of two wonders of physics: neutron stars and black holes .

The author tells how, with the advent of astronomy X – in a climate of trust and “cognitive optimism”, when stellar evolution was thought to be understood in every aspect -, astronomers discovered that in a dark corner of the sky, where there is a very ordinary small star when observed with a normal telescope, something shone with an enormously greater brightness X than might be expected. Data in hand, the astronomers soon realized that this something could have nothing to do with nuclear fusion processes. The discovery of this object, called Scorpius X-1 – along with that of another apparently similar but actually quite different object, Cygnus X-1– demolished most of the certainties that astrophysics had taken about thirty years to build. This is how, retracing the stages of the evolution of stars of great mass, the author describes how these stars are able to produce elements heavy up to iron and, having reached that point, find themselves collapsing on themselves until everything intervenes. another kind of pressure to stop the contraction.

«It has always struck me» writes Rezzolla, «that the final act of the bright and frenetic life of a massive star – as well as the catastrophic process that reveals its death – also marks the birth of one of the most fascinating objects in physics: a star of neutrons “. Perfect spheres of unimaginable density, with very high rotation frequencies and extremely high temperatures and magnetic fields, which the reader will be able to deepen in terms of observational properties, structure and internal composition, in a chapter entirely dedicated to these wonders of physics.

After the neutron stars it is the turn of black holes, samples of curvature, and you will be amazed by the fact that – although daily experience suggests that the more complex an object, organism or physical phenomenon, the greater the amount of information needed. to describe it – black holes are the simplest macroscopic physical objects of all. In addition to describing the physics of these objects, a dedicated chapter retraces the steps that led to the first image of a black hole , in the heart of M87, by the Event Horizon Telescope , explaining in detail why this image appears as we see it.

Having almost reached the end of the long journey, aware of what the curvature of spacetime is and what it entails in terms of gravity, in the last chapter the author deals with another interesting aspect: the propagation of perturbations in the curvature of spacetime. We are talking about gravitational waves , the revelation of which in 2015 marked the birth of the so-called multi-messenger astronomy, which opened a new window on the universe.

In the journey traveled with the author, you will find the answers to the many questions that each of us has asked himself at least once in his life, in addition to those that inevitably arise when reading the book. “What we experience in the course of our life on Earth is nothing more than a drop in the ocean of the physically possible”, concludes Rezzolla, and it is important not to limit the imagination: “Before advanced mathematics, complex simulations and sophisticated experiments – all however indispensable – comes the agility of our minds and their journeys of imagination. It is they who, more than anything else, allow us to extend the limits of knowledge ».

That gravity attracts is obvious to everyone, and after reading this book, it will become clear why. Like it or not, as the author states, we cannot escape gravity and its irresistible pull on our mind.

Featured image: Luciano Rezzolla is full professor of Theoretical Astrophysics and director of the Institute of Theoretical Physics at the Goethe Universität in Frankfurt. A member of the scientific committee of the Event Horizon Telescope project, his research helped capture the first photographic images of a supermassive black hole in 2019. Credits: Jürgen Lecher, Goethe-Universität Frankfurt

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Planetary Science

A Changing Martian Gathering (Planetary Science)

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The image of the Martian dunes celebrates the five years since the beginning of the Esa-Roscosmos ExoMars mission, which departed from Earth on March 14, 2016 and in scientific activity around the Red Planet since April 2018. This desert extract of seventy square meters is located in interior of the Lomonosov crater, in the northern hemisphere of Mars

Seeing it like this, ignoring the length scale at the bottom left, who could say where it was taken and what exactly this image depicts? With little imagination, one might think that the central part resembles the wrinkled skin of an elephant – of the rare Kenyan red elephant , for example, whose coloring is due to the dry baths that it usually takes while rolling on the ground in Tsavo East National Park. But perhaps someone will immediately connect red to a planet that – unlike ours – makes this color its characteristic trait. Yes, these seventy (approximately) square kilometers come from a wrinkled and arid – at least as much as the skin of the African specimen above – Martian soil.

It is a spectacular dune field in the center of the Lomonosov crater , deep in the northern hemisphere of Mars (65N, 351E), captured here by the Cassis camera aboard the Trace Gas Orbiter ( Tgo ) of the Esa and Roscosmos ExoMars mission . The shot dates back to 2 December 2020, and is part of an observation campaign that followed the evolution of the dune field during the year.

At that time, early December, the northern winter was coming to an end on Mars and the frost had begun to sublimate: in the regions we see darker, the frost has already given way to darker basaltic sand. It happens throughout the right portion of the image, also characterized by the presence of bright clouds that contrast with the ground below. Finally, you will notice that the crests of the dunes have an ordered orientation: it is the wind that generates this almost geometric effect. It is blowing – referring to the image – from the bottom left corner to the top right corner.

The image was chosen by ESA on the occasion of the five-year anniversary of the mission’s launch. In fact, Tgo was launched from the Baikonur Cosmodrome in Kazakhstan on March 14, 2016, arriving on Mars seven months later. He spent several months in aerobraking – taking advantage of the friction of the planet’s upper atmosphere to slow down – to then begin scientific operations in April 2018.

Tgo, as the name suggests, is an orbiter designed to carry out atmospheric analyzes thanks to its spectrometers (Nomad and Acs), which have, among other things, detected the presence of hydrogen chloride in the atmosphere of the Red Planet. The Cassis camera also captured more than 20,000 portraits of the surface, also useful as a guide for other tools. And last but not least, the orbiter also acts as a telecommunications satellite used by several landers and rovers for their routine connections.

Featured image: Dunes immortalized on 02 December 2020 by the Cassis camera aboard the Tgo orbiter. Credits: Esa / Roscosmos / Cassis

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