NASA's Perseverance rover has collected the first rock samples from Mars that could be returned to Earth in the first step towards answering if the red planet ever hosted life.
The samples come from the floor of Jezero crater, which was once a quiet lake fed steadily by a small river some 3.7 billion years ago.
Scientists believe that a watery Mars could have supported life billions of years ago.
The rocks analysed and stored for return to Earth have been altered by water, indicating evidence of a watery past on Mars.
University of Florida astrobiologist Amy Williams, who is one of the long-term planners for the Perseverance mission, said: “These kinds of environments on Earth are places where life thrives.
“The goal of exploring the Jezero delta and crater is to look in these once-habitable environments for rocks that might contain evidence of ancient life.”
The rover is now surveying the river delta to collect additional rock samples for the Mars Sample Return mission.
Geochemist David Shuster, professor of earth and planetary science at the University of California, Berkeley, said: “When that delta was deposited is one of the main objectives of our sample return programme, because that will quantify when the lake was present and when the environmental conditions were present that could possibly have been amenable to life.”
Led by NASA's Jet Propulsion Laboratory, Perseverance landed at the bottom of the Jezero crater in February 2021.
Since then scientists have been exploring the geological make-up of the crater floor using a suite of tools on board the rover that can take pictures of and analyse the rocks.
The researchers discovered the crater floor had eroded more than they expected.
The erosion exposed a crater made up of rocks formed from lava and magma, known as igneous rocks.
Before the mission, geologists expected that the floor of the crater was filled with either sediment or lava, which is molten rock that spilled onto the surface and cooled rapidly.
However, at two sites referred to as Seitah - the Navajo word for “amidst the sand” - the rocks appear to have formed underground and cooled slowly.
This suggests that whatever was covering them has eroded away over the past 2.5 to 3.5 billion years.
Dr Williams said: “We have organisms on Earth that live in very similar kinds of rocks.
“The aqueous alteration of the minerals has the potential to record biosignatures.”
NASA and the European Space Agency are planning to return the rock samples to Earth around 2033 when detailed studies can be carried out on the specimens.
Because the rock samples taken at the bottom of the crater likely predate the river delta, dating these rocks will provide important information about the age of the lake.
The findings are published in the Science journal.
