Another contender :)

A closeup of "leopard spots" on Mars seen by the Perseverance rover.
(Image credit: NASA/JPL-Caltech/MSSS)

In addition to Enceladus, Mars might make a play for life as well as leopard spots
might be the place proving life existed on Mars way back when. :)

Mars hasn't given us proof of life, but it has handed scientists a new kind of mystery.

On the western edge of Jezero Crater, NASA's Perseverance rover has been exploring Neretva Vallis, a river-carved valley that once fed a vast Martian lake. There, in an outcrop of ancient mudstone called the Bright Angel formation, the rover found one of its most intriguing targets yet: an arrowhead-shaped rock nicknamed Cheyava Falls, flecked with tiny black "poppy seeds" and ringed "leopard spots."

Closer analysis revealed that the strange markings are rich in organic carbon, iron, phosphorus and sulfur. More strikingly, scientists recently reported signs of vivianite (an iron phosphate) and greigite (an iron sulfide). On Earth, both minerals typically form through redox reactions — the electron-swapping processes that underpin all life. Plants rely on redox in photosynthesis, humans and other animals use it to extract energy from food during respiration, and microbes employ it to "breathe" metals in oxygen-starved settings such as deep-sea vents.

On our planet, such signatures are often the fingerprints of biology. On Mars, they remain a tantalizing "maybe" — chemical traces that could point to life, or could also arise from purely non-living processes. Either way, they mark a departure from the chemistry that scientists are used to seeing on the Red Planet.

"Whatever their origin, this is a very distinct chemistry than anything we've seen in ~20-25 years of roving the planet," Joel Hurowitz, a geoscientist at Stony Brook University in New York who led the recent study, told Space.com.

As stated before, Something's afoot. - Sherlock Holmes