Mars: “biogenic mechanisms… would seem to fit the observations quite well, while abiogenic ones are harder to come by.”

https://www.science.org/content/blog-post/life-maybe-mars-unless-we-change-our-minds

“We definitely need to study these formations more and try to model them here on Earth, but what we need to do for sure is make good on the sample-return part of the Perseverance mission … the proposals for how to go get them are in a state of expensive disarray”