NASA's Perseverance rover has collected a diverse set of rock samples in an area scientists believe is the perfect spot for finding signs of ancient microbial life on Mars.
The samples have the highest concentration of organic matter yet seen since the rover mission launched, but the US space agency says the findings do not "necessarily mean life".
The rover is exploring the Red Planet's sediment-rich Jezero Crater.
NASA said the crater had proven to be the "right location" for collecting rock samples after landing on Mars in February 2021.
"These first two science campaigns have yielded an amazing diversity of samples to bring back to Earth," Thomas Zurbuchen, NASA's associate administrator for science, said.
The crater is 45 metres wide, and hosts a delta — which NASA describes as an ancient fan-shaped feature that formed about 3.5 billion years ago.
The rover is currently investigating the delta's sedimentary rocks, formed in the once-watery environment.
A place where life on Mars 'could have thrived'
In its latest discovery, "Wildcat Ridge" is the name that has been given to a rock about one metre wide that likely formed billions of years ago as mud and fine sand settled in an evaporating saltwater lake.
"In the distant past, the sand, mud, and salts that now make up the Wildcat Ridge sample were deposited under conditions where life could potentially have thrived," Perseverance project scientist Ken Farley said.
"The fact the organic matter was found in such a sedimentary rock – known for preserving fossils of ancient life here on Earth – is important.
"However, as capable as our instruments aboard Perseverance are, further conclusions regarding what is contained in the Wildcat Ridge sample will have to wait until it's returned to Earth for in-depth study as part of the agency's Mars Sample Return campaign."
The samples are expected to arrive on Earth in 2033.
What's organic matter?
In 2013, NASA's Curiosity Mars rover found evidence of organic matter in rock-powder samples.
Organic molecules consist of a wide variety of compounds made primarily of carbon and usually include hydrogen and oxygen atoms.
While there are chemical processes that produce these molecules that do not require life, some of these compounds are the chemical building blocks of life, explains NASA.
It says the presence of these specific molecules is considered to be a "potential biosignature" — a substance that "could be evidence of past life" but it may also have been produced without the presence of life.
Perseverance, which is about the size of a car, gathers samples and either analyses the samples with its on-board laboratory, or it can save them for return to Earth by future missions.
NASA says the rover will also characterise the planet's geology and past climate, with the plan to pave way for human exploration.
