A paper published in the journal Icarus identifies distinct deposits of minerals called carbonates along the inner rim of Jezero, the site of a lake more than 3.5 billion years ago. On Earth, carbonates help form structures that are hardy enough to survive in fossil form for billions of years, including seashells, coral and some stromatolites — rocks formed on this planet by ancient microbial life along ancient shorelines, where sunlight and water were plentiful.

The possibility of stromatolite-like structures existing on Mars is why the concentration of carbonates tracing Jezero’s shoreline like a bathtub ring makes the area a prime scientific hunting ground.

Mars 2020 is NASA’s next-generation mission with a focus on astrobiology, or the study of life throughout the universe. Equipped with a new suite of scientific instruments, it aims to build on the discoveries of NASA’s Curiosity, which found that parts of Mars could have supported microbial life billions of years ago. Mars 2020 will search for actual signs of past microbial life, taking rock core samples that will be deposited in metal tubes on the Martian surface. Future missions could return these samples to Earth for deeper study.

In addition to preserving signs of ancient life, carbonates can teach us more about how Mars transitioned from having liquid water and a thicker atmosphere to being the freezing desert it is today. Carbonate minerals formed from interactions between carbon dioxide and water, recording subtle changes in these interactions over time. In that sense, they act as time capsules that scientists can study to learn when — and how — the Red Planet began drying out.

Measuring 28 miles (45 kilometers) wide, Jezero Crater was also once home to an ancient river delta. The “arms” of this delta can be seen reaching across the crater floor in images taken from space by satellite missions like NASA’s Mars Reconnaissance Orbiter. The orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars instrument, or CRISM, helped produce colorful mineral maps of the “bathtub ring” detailed in the new paper.

Scientists from NASA’s Mars 2020 mission and the European Space Agency-Roscosmos ExoMars mission are in the Australian Outback to hone research techniques before their missions launch to the Red Planet in summer 2020. They are hoping to better understand how to search for signs of ancient life on Mars. The Pilbara region of North West Australia is home to “stromatolites,” the oldest confirmed fossilized lifeforms on Earth.

“CRISM spotted carbonates here years ago, but we only recently noticed how concentrated they are right where a lakeshore would be,” said the paper’s lead author, Briony Horgan of Purdue University in West Lafayette, Indiana. “We’re going to encounter carbonate deposits in many locations throughout the mission, but the bathtub ring will be one of the most exciting places to visit.”

It isn’t guaranteed that the shoreline carbonates were formed in the lake; they could have been deposited before the lake was present. But their identification makes the site’s western rim, called “the marginal carbonate-bearing region,” one of the richest troves of these minerals anywhere in the crater.

The Mars 2020 team expects to explore both the crater floor and delta during the rover’s two-year prime mission. Horgan said the team hopes to reach the crater’s rim and its carbonates near the end of that period.

“The possibility that the ‘marginal carbonates’ formed in the lake environment was one of the most exciting features that led us to our Jezero landing site. Carbonate chemistry on an ancient lakeshore is a fantastic recipe for preserving records of ancient life and climate,” said Mars 2020 Deputy Project Scientist Ken Williford of NASA’s Jet Propulsion Laboratory in Pasadena, California. JPL leads the 2020 mission. “We’re eager to get to the surface and discover how these carbonates formed.”

Jezero’s former lake shoreline isn’t the only place scientists are excited to visit. A new study in Geophysical Research Letters points to a rich deposit of hydrated silica on the edge of the ancient river delta. Like carbonates, this mineral excels at preserving signs of ancient life. If this location proves to be the bottom layer of the delta, it will be an especially good place to look for buried microbial fossils.

The Mars 2020 rover will launch in July or August 2020 from Cape Canaveral, Florida. The Mars 2020 Project at JPL manages rover development for the Science Mission Directorate at NASA Headquarters in Washington. NASA’s Launch Services Program, based at the agency’s Kennedy Space Center in Florida, is responsible for launch management.

Mars 2020 is part of a larger program that includes missions to the Moon as a way to prepare for human exploration of the Red Planet. Charged with returning astronauts to the Moon by 2024, NASA will establish a sustained human presence on and around the Moon by 2028 through NASA’s Artemis lunar exploration plans.

The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, leads MRO’s CRISM investigation.

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Scientists analysed rainfall records from the 1870s to the present day and compared them against those featured in the Met Office’s UK Climate Projections 2018 (UKCP18) report.

Their findings show that there has been a significant increase in spring, autumn and winter precipitation, greatest in upland windward areas of the region, with winter increases broadly consistent with UKCP18 projections.

However, their results show for spring, summer and autumn precipitation there could be large divergence by the mid to late 21st century, with the observed mismatch greatest in upland areas.

The study, published in Climate Research, was conducted by research student Thomas Murphy and academics from the University’s School of Geography, Earth and Environmental Science and School of Biological and Marine Sciences.

Dr Paul Lunt, Associate Professor in Environmental Science and one of the study’s authors, said: “Our study helps to contextualise the latest UK climate change projections, and suggest caution is required when making assumptions on climate impacts based on climate models. Current models predict that by 2050, summer rainfall on Dartmoor will fall by as much as 20%, but our results from past records show that in the uplands it is on an upward trajectory.

“This study shows there have been significant increases in spring, autumn, winter and annual precipitation for upland regions in South West England between 1879 and 2012. Meanwhile the moderate increases in summer precipitation represent a deviation from the drier summers predicted within current and previous climate models.

“In that regard, this research highlights the complex challenges facing those trying to predict the effects of climate change. Upland areas are among the most important UK regions in terms of biodiversity and carbon sequestration, but they are also the most vulnerable to increased precipitation.”

Upland areas more than 300m above sea level cover around one third of the UKs land area and are considered of national and international importance due to their biodiversity and cultural heritage. They are also the source of 68 per cent of the UK’s freshwater and have a significant role in flood risk mitigation.

Levels of precipitation in the uplands are typically twice the average of those for UK lowland sites. As a result, there contribution to flood risk and downstream flood damage is disproportion to their catchment area.

The research focused on Dartmoor and Plymouth, aiming to scrutinise one of the longest running upland and lowland precipitation records anywhere in Western Europe. It also looked at shorter-term records from a number of upland sites.

The results show that over the past 130 years rainfall in upland areas has increased in all seasons, with spring, autumn and winter increasing by more than 12%. In Plymouth, rainfall has increased by more than 5% in all seasons apart from summer, where there has been slight decrease. Annual levels in the uplands and Plymouth have risen by 11% (226mm) and 5% (46mm) respectively over the same period.

The researchers also say that while these results are important at a local scale, they are also relevant for upland coastal sites across the North East Atlantic.

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The research team is the first to combine 3D climate modeling with atmospheric chemistry to explore the habitability of planets around M dwarf stars, which comprise about 70% of the total galactic population. Using this tool, the researchers have redefined the conditions that make a planet habitable by taking the star’s radiation and the planet’s rotation rate into account.

Among its findings, the Northwestern team, in collaboration with researchers at the University of Colorado Boulder, NASA’s Virtual Planet Laboratory and the Massachusetts Institute of Technology, discovered that only planets orbiting active stars — those that emit a lot of ultraviolet (UV) radiation — lose significant water to vaporization. Planets around inactive, or quiet, stars are more likely to maintain life-sustaining liquid water.

The researchers also found that planets with thin ozone layers, which have otherwise habitable surface temperatures, receive dangerous levels of UV dosages, making them hazardous for complex surface life.

“For most of human history, the question of whether or not life exists elsewhere has belonged only within the philosophical realm,” said Northwestern’s Howard Chen, the study’s first author. “It’s only in recent years that we have had the modeling tools and observational technology to address this question.”

“Still, there are a lot of stars and planets out there, which means there are a lot of targets,” added Daniel Horton, senior author of the study. “Our study can help limit the number of places we have to point our telescopes.”

The research will be published online Nov. 14 in the Astrophysical Journal.

Horton is an assistant professor of Earth and planetary sciences in Northwestern’s Weinberg College of Arts and Sciences. Chen is a Ph.D. candidate in Northwestern’s Climate Change Research Group and a NASA future investigator.

The ‘Goldilocks zone’

To sustain complex life, planets need to be able to maintain liquid water. If a planet is too close to its star, then water will vaporize completely. If a planet is too far from its star, then water will freeze, and the greenhouse effect will be unable to keep the surface warm enough for life. This Goldilocks area is called the “circumstellar habitable zone,” a term coined by Professor James Kasting of Penn State University.

Researchers have been working to figure out how close is too close — and how far is too far — for a planet to sustain liquid water. In other words, they are looking for the habitable zone’s “inner edge.”

“The inner edge of our solar system is between Venus and Earth,” Chen explained. “Venus is not habitable; Earth is.”

Horton and Chen are looking beyond our solar system to pinpoint the habitable zones within M dwarf stellar systems. Because they are numerous and easier to find and investigate, M dwarf planets have emerged as frontrunners in the search for habitable planets. They get their name from the small, cool, dim stars around which they orbit, called M dwarfs or “red dwarfs.”

Crucial chemistry

Other researchers have characterized the atmospheres of M dwarf planets by using both 1D and 3D global climate models. These models also are used on Earth to better understand climate and climate change. Previous 3D studies of rocky exoplanets, however, have missed something important: chemistry.

By coupling 3D climate modeling with photochemistry and atmospheric chemistry, Horton and Chen constructed a more complete picture of how a star’s UV radiation interacts with gases, including water vapor and ozone, in the planet’s atmosphere.

In their simulations, Horton and Chen found that a star’s radiation plays a deciding factor in whether or not a planet is habitable. Specifically, they discovered that planets orbiting active stars are vulnerable to losing significant amounts of water due to vaporization. This stands in stark contrast to previous research using climate models without active photochemistry.

The team also found that many planets in the circumstellar habitable zone could not sustain life due to their thin ozone layers. Despite having otherwise habitable surface temperatures, these planets’ ozone layers allow too much UV radiation to pass through and penetrate to the ground. The level of radiation would be hazardous for surface life.

“3D photochemistry plays a huge role because it provides heating or cooling, which can affect the thermodynamics and perhaps the atmospheric composition of a planetary system,” Chen said. “These kinds of models have not really been used at all in the exoplanet literature studying rocky planets because they are so computationally expensive. Other photochemical models studying much larger planets, such as gas giants and hot Jupiters, already show that one cannot neglect chemistry when investigating climate.”

“It has also been difficult to adapt these models because they were originally designed for Earth-based conditions,” Horton said. “To modify the boundary conditions and still have the models run successfully has been challenging.”

‘Are we alone?’

Horton and Chen believe this information will help observational astronomers in the hunt for life elsewhere. Instruments, such as the Hubble Space Telescope and James Webb Space Telescope, have the capability to detect water vapor and ozone on exoplanets. They just need to know where to look.

“‘Are we alone?’ is one of the biggest unanswered questions,” Chen said. “If we can predict which planets are most likely to host life, then we might get that much closer to answering it within our lifetimes.”

Horton and Chen are both members of CIERA (Center for Interdisciplinary and Exploratory Research in Astrophysics).

The study was supported by the Future Investigators in NASA Earth and Space Science and Technology graduate research award (80NSSC19K1523) and a NASA Habitable Worlds grant (80NSSC17K0257). Computational work was completed at Northwestern’s QUEST high-performance computing facility.