NASA’s Perseverance rover has found complex carbon compounds in a Martian crater that had previously shown tantalising possible signs of ancient life. On Earth, these compounds are typically associated with dead organisms, but scientists say it is too early to draw the same conclusion here as these compounds are also found in lifeless environments, like on meteorites.

In 2024, Perseverance entered a rocky outcrop, called Bright Angel, near what appeared to be an ancient riverbed that once fed a lake inside Jezero crater. Several rocks photographed by the rover displayed unusual spotted patterns, which NASA scientists called “leopard spots” and “poppy seeds”. These markings, which are largely or entirely formed of dark, circular blots of up to a millimetre in size, look very similar to the patterns left behind by ancient microbial activity on Earth.

Although non-biological sources couldn’t be ruled out, the markings are some of the best candidates we have for potential ancient life on Mars. But scientists lacked comprehensive information on the chemical make-up of these patterns or how widely distributed they were in the Bright Angel formation.

However, Perseverance carries measurement tools that can provide more chemical context about the rocks it encounters, such as the SHERLOC instrument, which uses the reflected light from an ultraviolet laser to identify elements and compounds in a rock sample.

Now, at the Planetary Science Institute in Tucson, Arizona, and her colleagues have used SHERLOC to identify large, complex carbon-containing molecules, called macromolecular carbon, on the surface of the marked rocks in the Bright Angel formation, as well as in a separate rock in the same formation around 100 metres away.

“On Earth, macromolecular carbon is often found in extremely old rocks and, in some cases, it is the only organic evidence of past microbial life,” says Murphy. “Finding these organic macromolecules on Mars and other planetary bodies helps us determine whether the necessary chemical ingredients and environmental conditions to support life have ever existed there.”

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The existence of these carbon compounds can’t imply a biological origin by themselves, as they are also found in places like meteorites, says at the University of Westminster in London. However, Murphy and her colleagues also discovered that the compounds were associated with carbonate and sulphate minerals, which tend to form in water-rich environments, another key ingredient for life. “It’s giving us information about the geological context of where those organics are being found,” says Dartnell.

Jezero crater was already suspected to have been water-rich at some point, so the fact that these carbon compounds existed here is unsurprising by itself, says team member at NASA’s Jet Propulsion Laboratory in California. However, macromolecular carbon has never been seen on the surface of a rock like this, says Uckert, which might imply that it is unusually resistant and different from other carbon-bearing compounds that have been found on Mars.

“Its ubiquitous presence within mudstones at Bright Angel compared with observations elsewhere in the crater was surprising,” says Uckert. Although it is currently unclear why that should be the case, this is a good sign for the possibility of finding other signs of past life, says Dartnell. “This detection confirms that complex organics, like these macromolecular deposits, can stick around for long periods of time.”

While the SHERLOC instrument can identify macromolecular carbon, it can’t give detailed information on the actual make-up of the compounds beyond saying that they are carbon-rich, says at the University of Edinburgh, UK. “We would need to get the samples back to Earth to figure out if the carbon in these rocks was of biological origin,” he says.

The liquid water ocean hidden underneath the icy crust of Enceladus has long made this moon of Saturn one of the best prospects in the hunt for extraterrestrial life – and it just got even more promising. The discovery of heat emanating from the frozen moon’s north pole hints the ocean is stable over geological timescales, giving life time to develop there.

“For the first time we can say with certainty that Enceladus is in a stable state, and that has big implications for habitability,” says at the University of Oxford. “We knew that it had liquid water, all sorts of organic molecules, heat, but the stability was really the final piece of the puzzle.”

Howett and her colleagues used data from NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017, to hunt for heat seeping out of Enceladus. Its interior is heated by tidal forces as it is stretched and crunched by Saturn’s gravity, but so far this heat has only been caught leaking out of the south polar regions.

For life to have developed in Enceladus’s ocean, it would require balance: the ocean should be putting out as much heat as is being put in. Measurements of the heat coming out of the south pole don’t account for all of the heat input, but Howett and her team found the north pole is about 7°C warmer than we previously thought. Combined with the heat radiating from the south pole, that matches the total almost exactly – the ice shell is thicker around the equator, so heat only escapes in significant amounts at the poles.

This means the ocean should be stable over long periods of time. “It’s really hard to put a number on it, but we don’t think it’s going to freeze out anytime soon, or that it’s been frozen out anytime recently,” says Howett. “We know life needs time to evolve, and now we can say that it does have that stability.” Actually finding that life, if it is there, is another story entirely. But both NASA and ESA have missions in the works to look for it over the coming decades.

Mysteries of the universe: Cheshire, England

Spend a weekend with some of the brightest minds in science, as you explore the mysteries of the universe in an exciting programme that includes an excursion to see the iconic Lovell Telescope.

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The New Scientist Book Club has been reading Adrian Tchaikovsky’s Alien Clay, a science fiction epic in which a political prisoner must unlock the secrets of a strange and dangerous planet. Best known for his series Shadows of the Apt and for his Hugo Award-winning Children of Time series, Tchaikovsky has arguably cemented himself as a master of science fiction. This week, our fiction reviewer Emily H. Wilson caught up with Tchaikovsky to delve into his disciplined writing process, the inevitable interweaving of politics and science, and the true definition of “science fiction”.

Read more: Adrian Tchaikovsky: “Could life have gone any other way?”