When the Mars 2020 rover lands on the Red Planet in February 2021, it will touch down in Jezero Crater, the site of a lake that existed 3.5 billion years ago. Now, two research teams have identified areas in Jezero Crater where the rover might find signs of ancient life.
The crater is 28 miles wide and once contained a river delta, traces of which can still be seen from images taken by the Mars Reconnaissance Orbiter.
In one study, researchers discovered the signature of carbonate minerals in the crater’s inner rim. On Earth, carbonates are associated with seashell, coral and stromatolite fossils found scattered along what were once shorelines of ancient lakes and bodies of water.
The researchers used images from the Mars orbiter’s camera to create mineral maps. The orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars Instrument, called CRISM, was key to finding carbonates on the rim, according to the study published Tuesday in the journal Icarus.
Scientists are intrigued by these carbonate deposits on Jezero’s inner rim because they seem to suggest the carbonates sit on an ancient shoreline. And the carbonates could also contain information about how Mars transformed from habitable to inhospitable (the planet once could support liquid water on the surface and maintained a thick atmosphere, but now it has an incredibly thin atmosphere and is a harsh, freezing and barren desert).
The 2020 rover will be able to investigate these carbonates because its instruments are up to the task. Another rover, called Curiosity, was designed to help scientists determine if Mars could have supported life in the past. The 2020 rover carries that mission forward with the hopes of finding evidence of this potential ancient life. It will collect and store rocky core samples in metal tubes that can be returned by future missions.
“CRISM spotted carbonates here years ago, but we only recently noticed how concentrated they are right where a lakeshore would be,” said Briony Horgan, lead study author from Purdue University. “We’re going to encounter carbonate deposits in many locations throughout the mission, but the bathtub ring will be one of the most exciting places to visit.”
The presence of carbonates isn’t a guarantee that they originated from the lake because they could have existed there before the lake formed. But the site is worth investigating further during the rover’s two-year mission, which includes exploring the delta and floor of the crater.
“The possibility that the ‘marginal carbonates’ formed in the lake environment was one of the most exciting features that led us to our Jezero landing site. Carbonate chemistry on an ancient lakeshore is a fantastic recipe for preserving records of ancient life and climate,” said Ken Williford, Mars 2020 deputy project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “We’re eager to get to the surface and discover how these carbonates formed.”
A second study, published Tuesday in the journal Geophysical Research Letters, also revealed the detection of hydrated silica on the edge of the river delta using CRISM. This mineral acts like a record of biosignatures.
“Using a technique we developed that helps us find rare, hard-to-detect mineral phases in data taken from orbiting spacecraft, we found two outcrops of hydrated silica within Jezero Crater,” said Jesse Tarnas, study author and doctoral student at Brown University. “We know from Earth that this mineral phase is exceptional at preserving microfossils and other biosignatures, so that makes these outcrops exciting targets for the rover to explore.”
The ancient delta is intriguing to scientists because on Earth, river deltas contain diverse material and can preserve signs of past life. The presence of the hydrated silicates in the delta makes it even more likely that the rover could find evidence of ancient life if it existed on Mars.
“The material that forms the bottom layer of a delta is sometimes the most productive in terms of preserving biosignatures,” said Jack Mustard, study co-author and professor at Brown University. “So, if you can find that bottomset layer and that layer has a lot of silica in it, that’s a double bonus.”
The rover’s instruments will be able to detect if the minerals formed in the delta or if they were carried in the watershed that fed the delta.
“We can get amazing high-resolution images and compositional data from orbit, but there’s a limit on what we can discern in terms of how these minerals formed,” Tarnas said. “Given instruments on the rover, however, we should be able to constrain the origin of these deposits.”
The rover is also capable of conducting chemical analysis of the minerals, linking its data with data from the orbiter and even searching for complex organic material.
“If these deposits present themselves in the form of rocks that are big and competent enough to drill into, they could be put into the cache,” Mustard said. “This work suggests that they’d be a great sample to have.”