Rock samples collected by Perseverance rover hold tantalising clues about water and life on Mars


Rock samples collected by NASA’s Perseverance rover from ancient Martian lake beds could finally provide us with clues to the existence of conditions conducive to harbouring life on the Red Planet.

Since September 2021, Perseverance has been busy collecting samples in the Jezero Crater, an area that is believed to contain evidence of an ancient river delta and lake bed.

NASA scientists have started to investigate the geological makeup of the craters using the tools on board the rover that can take pictures of, and analyse, the basic chemical composition of rocks.

Although these rocks are being stored on the Red Planet, ahead of a return mission in the 2030s, scientists are already taking stock of the valuable insights they may reveal about Mars’s watery past.

“Discovering when that delta [in the Jezero Crater] was deposited is one of the main objectives of our sample return programme,” said Prof David Shuster, a member of NASA’s science team.

“That will quantify when the lake was present and when the environmental conditions were present that could have been amenable to life.”

The mission scientists discovered that rocks collected from four sites on the crater floor are igneous cumulate rocks, which are formed by the cooling of molten magma.

The name ‘cumulate’ refers to a group of rocks that are formed by crystal accumulation, and it’s hoped that the study of these rocks will not only reveal when a lake was present at the Jezero Crater, but also shed light on when major events occurred in the Martian climate’s timeline.

“The study of the rocks will address some major questions,” said Prof Kenneth Farley, Perseverance’s project scientist.

“When was Mars’s climate conducive to lakes and rivers on the planet’s surface? And when did it change to the very cold and dry conditions we see today?”

Prior to Perseverance, geologists expected to find Jezero Crater’s floor filled with sediment or lava – molten rock that spilled onto the surface and cooled rapidly.

Instead, at one pair of sample sites, known as Séítah, they discovered rocks that appeared to have formed underground and cooled slowly.

This suggested that whatever was covering them had eroded away over 2.5 to 3.5 billion years. The crystal structure of this rock revealed millimetre-sized grains of a substance that could only have been formed by slow cooling.

Samples from a second pair of sites at Máaz, were found to be igneous too, but with a different composition, suggesting they may have come from the upper layer of the magma lake. Scientists believe that both these sets of samples – from Séítah and Máaz – were formed by the action of water.

The Máaz rocks were found to contain pockets of minerals that may have condensed from salty brine, while the Séítah rocks may have reacted with carbonated water, according to chemical analyses onboard the rover.

We’ll have to wait until at least 2031 for more precise details about the times when these various layers might have formed, following laboratory analysis back on Earth, but the evidence about Mars’s watery past is already stacking up.

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