Jerezo crater contains a delta with abundant sedimentary layers that are the kind most likely to preserve fossil life, and so is one of three landing sites in the running for the Mars 2020 mission. The image has been colored to better show features of the site. (NASA)

One of the great successes of the Curiosity mission to Mars is that the rover landed at what turned out to be a goldmine of a location.

The mission has once and for all determined that the planet was habitable at least during its early days, that it contains the organic building blocks of life, and that liquid water ran and formed lakes.  And this leaves out the more basic Mars science that some day will some day produce new headline results.

The process of anointing a successor destination for NASA’s 2020 rover mission to Mars has been going on for several years now, and the field was narrowed to three possibilities earlier this year.

Because some of the primary goals of the 2020 mission differ from those of the Curiosity mission, the potential landing sites are unlike Gale Crater and all share certain features that are, not surprising, promising in terms of the new goals.  What’s new is the requirement that the 2020 mission will search for biosignatures of life in the ancient rocks and to identify, pick up and store rocks samples for later return to Earth.

Given those (and other) science goals, the leaders of the Mars 2020 mission — and the large community of scientists eager to become a formal or informal part of the mission — have been looking for sites where water was clearly present in the distant past and where conditions seem best for actually preserving fossil microbial biosignatures that may have been present.

This is quite a dramatic change, and will be the first NASA mission sent to look for life — albeit fossilized and ancient life — since the Viking missions of four decades ago.

“What we’re down to now is three sites featuring different kinds of ancient water settings,” said Kenneth Williford of NASA’s Jet Propulsion Lab.  He’s deputy project scientist for the 2020 mission and a specialist in identifying fossil remnants of lifeforms in ancient Earth rocks.

“On the list we have a site that was clearly a river delta, one that had a large concentration of subsurface water, and another that may be the site of a possible hot spring. … Read more