NASA has big plans for its upcoming Mars 2020 rover, launching in the summer of 2020 (duh) and arriving at the red planet the following February. Picking a landing site for a mission like this effectively shows what type of scientific studies you want to prioritize. To that end, the selection of Jezero Crater, announced this week, affirms the desire of NASA and its partners to learn if Mars was (or is) home to extraterrestrial life of some kind.
That’s not spin—it’s something scientists are expressing themselves. “There’s a wide diversity of outcrop and rock types accessible at this site, which the Mars 2020 rover will be able to interrogate to vastly improve our understanding of the ancient Martian surface environment, and whether it might preserve any evidence for past life,” says Timothy Goudge, a planetary scientist at The University of Texas at Austin. He calls Jezero “an incredible landing site that will provide us with immense opportunity to do very compelling and interesting science.”
The 28-mile-wide crater was selected from out of three finalist sites on the Martian surface, which included Northeast Syrtis (home to buried hydrothermal systems) and Columbia Hills (notable for being home to former hot springs). A dark horse candidate, Midway (also home to ancient hydrothermal activity) was also considered. Jezero Crater and Northeast Syrtis were the frontrunners, but neither had a clear lead in support, and Thomas Zurbuchen, the associate administrator for NASA’s Science Mission Directorate, ultimately chose Jezero.
It’s not hard to see why, given Jezero’s location. “We think we can actually roll out of Jezero and onto the surrounding plains and to get to one of the other landing sites, Midway—which is a totally different kind of geological environment,” says Briony Horgan, an assistant professor of planetary science at Purdue University who helped evaluate the candidates. “I think the whole team is excited about that possibility in particular. The kind of samples we can get from both of those sites is a total hole-in-one. It’ll just be an incredible find, not just for Mars but for essentially the whole solar system.”
But Jezero was popular to begin with because it’s probably one the oldest preserved lake basins on Mars. Briony and her colleagues think it was an active lake with a river system during the Noachian Period (the Martian geological era ranging between 4.1 and 3.7 billion years ago), when Mars boasted the most surface water activity in its history. Two main river valleys would have fed water into the lake basin, and an outlet valley would have allowed water to drain out.
“When the lake was present, it likely would have provided a habitable environment that life as we know it would have been able to survive in,” says Goudge. “The question of whether or not it actually does preserve evidence for past life is a huge outstanding question that is driving much of the science that will be done by the Mars 2020 rover mission.”
Although the water is long gone, Jezero sports a prominent outcrop of a preserved river delta leading into the former lake, which probably deposited a walloping amount of sediments carrying old minerals and elements into former lakebed. “These types of sedimentary deposits record the conditions of formation over their lifetime of activity, and as the rover marches up different layers, it will be able to read the record of what this site was like several billion years ago,” says Goudge. “When deltas collect material from their watershed, the process of transporting that material in the river and depositing it in the Jezero lake would have led to the concentration of any existing organic matter within specific layers of the deposit, so we have a very good understanding of where to go to explore for possible biosignatures as soon as we land.”
But one of Jezero’s most compelling qualities is that it’s home to carbonates, which could lead us to more concrete signs of Martian life. Mars has a carbon dioxide atmosphere, and when it rains, it produces carbonic acid, which in turn produces carbonate on the surface.
On Mars, carbonates are inexplicably rare. Even more inexplicable, they’re actually more abundant in Jezero Crater. According to Horgan, they may have precipitated out of the water itself. “A rapid precipitation of minerals like that in water does a really nice job of trapping whatever is living in the water,” she says. Basically, the carbonate deposits could have preserved any Martian microbes that were living at the bottom of the lake or by the shoreline, or any biosignatures those lifeforms produced. “We could potentially observe those things directly with the rover and its instruments onboard. That’s a really exciting possibility.”
And to pile on top of all that, there might be a lava flow situated on top of all these lake sediments. A sample of the lava flow could help us better understand the geological history of Mars, and also help us narrow down the age of Jezero and other craters found throughout the red planet.
“All of these things together make Jezero just really diverse and interesting,” says Horgan. “It’s always been popular for those reasons.” Mars 2020’s technology gives us a chance to actually study those components in depth.
And what we’ll learn out of Jezero will shape what we know about Mars as a whole. The timeline of water in Jezero coincides with the timeline of water activity elsewhere on the planet. The delta in particularly was able to collect material from a large catchment area and basically feed it all into one location, which means the rover has a chance to sink its robotic teeth into a really diverse array of materials. We’ll also be able to learn more about how amenable the Noachian climate was to burgeoning life all over the planet. “Those are huge questions not just for Jezero, but for Mars in general,” says Horgan.
What makes Mars 2020 so special? Well, remember earlier this year when the Curiosity rover managed to find evidence of ancient organic matter embedded in the red planet’s rocks? Mars 2020 possesses a suite of instruments and onboard laboratory equipment that can follow up on those sorts of discoveries in unprecedented detail. “The rover will have this unparalleled ability to do high-resolution geology and astrobiology,” says Horgan. She’s excited to see instruments like SHERLOC (a raw spectrometer able to detect the presence of organics in rocks) and PIXL (an x-ray spectrometer that can identify individual elements in sample) to look not only for biosignatures and evidence of ancient life, but also tell where those things are located within the rock itself.
There’s also so much science we can do with a rover, and that’s another reason there’s so much excitement surrounding the new mission. “We’re trying to do astrobiology on the surface, and that’s really the point of the Mars 2020 mission,” says Horgan. But with Mars 2020, “we’re also going to be collecting samples that we’ll bring back to Earth eventually on another mission. Because of that, it’s going to be an interesting mission—we’re going to have competing priorities that persuade us to stay and study the rocks in a few places, or zip around and collect as many samples as possible. But I’ve been really impressed with the technology of this rover, and I really think we could do both.”
