Let's talk about the search for life on Mars and why Perseverance is so exciting! We know we're looking for evidence of past life, but what does that actually look like?

Jezero crater was specifically chosen as the landing site because it has one of the best preserved delta deposits anywhere on mars. The crater has both an inlet and outlet, meaning that we knew water was flowing throughout the crater in Mars' past.

This is important! Shallow lacustrine environments are particularly well suited for microbial life and - this is the kicker - the preservation of those microbial colonies. But what exactly are we preserving? In particular, we're interested in two things:

molecular biomarkers and microfossils. Molecular biomarkers are formed when molecules formed by organisms undergo a process called diagenesis - the process of compaction that turns sediments into sedimentary rocks. But let's focus on microfossils:

Microfossils are fossils left by organisms when mineral enriched water seeps into the sediment where microbes are deposited, encasing them in the rock. They show the outline of both individual microbes, as well as the larger scale structures that these microbes form.

So we have some questions: 1) what can these microfossils tell us 2) how are these microfossils preserved and 3) what factors make Jezero crater and Perseverance ideal for finding microfossils and proving whether or not life ever existed on Mars?

1) Microfossils can tell us a lot! The shape and morphology of the microbes and the colonies they form can tell us about the environment they lived in, temperature, pressure, metabolism, and other parts of the ecosystem that may not have been preserved.

2) Until recently, it was thought that microbes were only preserved in environments that were supersaturated in minerals like silica, which would precipitate out of the water, encasing the microbes that lived there in chert deposits, like we see at Yellowstone today

However, my undergraduate thesis (and first by my undergraduate thesis advisor, Dr. Kelsey Moore of the JPL abcLab) showed that cyanobacteria could mediate their own preservation BELOW saturation levels in shallow tidal environments. Why does this matter?

This ties into 3) Jezero crater has one of the best preserved delta deposits anywhere on Mars - very similar to the shallow depositional environments shown to be ideal for preservation by Moore et al. and Morgenstein and Moore et al.

If life ever existed on Mars, there's a good chance we find it in Jezero Crater. The sensing and sampling suite on the Perseverance Rover makes it incredibly well equipped to find microfossils on Mars.

Finding a microfossil would be unambiguous proof that there was life on another planet. But what happens if we don't find it? Luckily, we have some more tricks up our sleeves - legged robots. Rovers are great for a lot of reasons: they're stable, energy efficient, and reliable.

However, they have one key drawback: mobility. Rovers can only go where their wheels can get traction. Steep outcrops and large boulders are insurmountable. Instead, I'm working with NASA JPL to develop legged robot capabilities to explore environments on Mars that are currently

inaccessible to rovers. These steeper outcrops allow us to sample a much wider section of Mars' geologic past. The Mars 2020 mission is INCREDIBLY exciting. It lays the groundwork for the first planetary sample return mission later this decade, and paves the way for

human exploration of Mars. Just as Sojourner, Curiority, and Opportunity created the foundation for Perseverance, Perseverance will enable a depth of astrobiological exploration never before possible. Congrats to the JPL team, I can't wait to see what we discover!

References (papers and images):
Allwood 06, Hofmann 76, Drozd 19, Morgenstein 18, Moore 20, Morgenstein 20, Morgenstein (in prep), Knoll 13, NASA JPL 19, NASA JPL 21, Bosak 20, Gupta 20, CSIRO 19, CSIRO 20