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Mapping of ancient lake shores, different minerals and violent volcanism of Jezero crater

Two studies based on ESA’s Mars Express observations of Jezero Crater, the future landing site for NASA’s 2020 Mars Perseverance rover, have shed light on how and when this fascinating area formed and identified regions best suited to detect ancient signs of life.

NASA’s 2020 Perseverance Mars rover will search for signs of past life on Mars and collect samples for a future return to Earth. NASA and ESA are currently working together on the mission design to bring these samples back to Earth by 2031.

Two studies based on data from another space mission, ESA’s Mars Express, which has been orbiting the Red Planet since 2003, have identified which parts of the rover’s landing site are most likely to retain ancient signs of life, climate, water and volcanism. Both studied a part of Mars’ surface known as Nili Fossae and, more specifically, a crater within this area called Jezero.

The Jezero crater contains a delta, clear evidence that water once flowed there in the form of an ancient lake, and contains large amounts of both olivine and carbonate minerals. Carbonates form in the presence of water and are known to trap “biological signatures,” the signatures of life, while olivine is present in magmatic rocks and can be used to explore and accurately date Mars’ volcanic past.

“We have known for decades that Nili Fossae is a rather unique part of Mars and that Jezero crater was chosen as the landing site for the Perseverance rover because of this uniqueness,” says Lucia Mandon of the Laboratoire de Géologie de Lyon (Terre, Planètes, Environnement) in France and author of a study on the mineralogy, age and evolution of the Nili Fossae region.

“However, while this part of Mars has been well studied, scientists were still unsure how and when it formed, or how it came to contain all this olivine- and carbonate-rich material. In fact, at least six different scenarios have been proposed over the past two decades.”

To resolve this uncertainty, Lucia Mandon and colleagues analyzed observations of the Nili Fossae region collected by ESA’s Mars Express and NASA’s Mars Reconnaissance Orbiter (MRO); a mix of high-resolution images, topographic data, mineralogical data and thermal data. They thus discovered that the olivine-rich rock substrate in the region around Jezero crater covers at least 18,000 square kilometers and was formed about 3.8 billion years ago.

Lucia Mandon adds:
“One of the most popular theories about its formation suggests that the olivine-containing material formed as a layer of molten rock, created by the giant impact nearby that produced the huge Isidis Basin, but our chronology reveals that the olivine-rich bedrock formed tens of millions of years or more after this impact.

However, we believe that this impact made the crust brittle and more prone to volcanism. After examining all plausible scenarios, we found that the Nili Fossae region was most likely sculpted by massive eruptions of ash and other material ejected by giant volcanoes. the volume erupted is colossal, more than 1000 times larger than that of the Vesuvius event that destroyed Pompeii in 79 AD.”

This suggests that the common view of Martian volcanism, in which volcanic activity occurred primarily through lava flows with only a few instances of explosive activity, may not be entirely accurate.

Lucia Mandon and colleagues also mapped the carbonates present in Nili Fossae, detecting some of the strongest concentrations right near the landing site of the Perseverance rover. These minerals are known to form in fairly neutral waters, environments that are favorable for most forms of life we know on Earth.

“Carbonates that form along the shores of a lake on Earth are fantastic for preserving biological signatures,” says Briony Horgan of Purdue University, USA, lead author of a supplemental paper on the distribution and origin of carbonate-containing rocks in Jezero Crater.

Also Briony Horgan adds:
“Carbonate-producing alkaline lakes on Earth are almost always inhabited by stromatolites, large mineral domes created by layers of microbial mats, which are well known to have preserved some of the clearest and oldest biological traces left on our planet billions of years ago. While we don’t know if we will find stromatolites on Mars, we do know that this lacustrine environment would be a great place to look for biological traces and organic molecules that formed anciently on Mars.”

Jezero Crater is the only known location on Mars where carbonates have been clearly detected in the vicinity of features indicating the presence of an ancient lake. Briony Horgan and colleagues studied the crater using data from Mars Express and MRO to find out whether carbonates formed within this lake or as a result of other processes, such as alteration due to rain.

They found that while carbonates are present throughout the crater, there is a ring of strong carbonate signatures at altitudes where the shoreline of the ancient lake should have been. This suggests that those particular carbonates probably precipitated onto the lake shore, making them particularly interesting for both the study of water and potential past life on Mars.

Then Briony Horgan adds:
“These carbonates will be a key target for the Mars 2020 and Mars Sample Return missions because of their high potential for preserving biological signatures.
We hope to be able to reach the littoral area during the primary Mars 2020 mission. This ring of carbonates at the old water level along the western edge of Jezero will be a particularly exciting part of the crater to explore.”

One of the key pieces of evidence for these possible carbonates formed on the shores of the lake was the result of topography derived from the Mars Express high-resolution stereo camera (HRSC). Briony Horgan and colleagues used topographic data collected by Mars Express from orbit to determine the altitude of these minerals within the crater, which is essential to determining how they had formed.

In addition, this research will clarify the history and nature of a crucial part of the Martian surface. When Perseverance lands in Jezero crater, it will examine both the olivine-rich rock substrate and carbonate ring studied by Lucia Mandon, Briony Horgan and colleagues; the rover team is also planning to collect samples of the rocky floor for future return to Earth.

Resumes Lucia Mandon:
“With a mission that brings samples back to Earth, we would then be able to accurately date these samples in a laboratory and compare this age to the age we inferred from orbit.
This would allow us to calibrate the entire Martian time system and is a key example of why I find the Mars Sample Return mission so exciting and valuable.”

Launched 17 years ago, Mars Express has been orbiting Mars since December 2003 and carries a suite of advanced instruments on board. These studies used data from the HRSC camera and the OMEGA (Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité) spectrometer.

Dmitri Titov, ESA’s Project Scientist for Mars Express, adds:
“While HRSC maps the topography of Mars’ surface down to a few tens of meters per pixel, OMEGA produces detailed visible and near-infrared images that researchers can use to identify surface minerals.

These instruments, along with those on the MRO, have been instrumental in accurately mapping the extent of carbonate and olivine material within Jezero crater, as they can cover large areas of the surface and provide detailed information about its topography and mineralogy.

It is extremely exciting to consider how the many missions currently on Mars will support and complement the findings of the Perseverance rover when it reaches this scientifically exciting area of the Martian surface. Mars Express has 16 years of experience on the planet, which will prove invaluable for future exploration and efforts to bring Martian samples back to Earth.”

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