From orbital images, scientists have determined that Jezero once hosted a lake, about the size of Lake Tahoe or Lake Winnipeg, that had a watershed of over 30,000 square kilometers. It was an open basin, with two inflow channels and one outflow channel. To form a delta, water must flow through an area for a very long time, for thousands of years or more. The longer liquid water is present in an environment, the more hospitable it would have been for life. Deltas are also great for preserving evidence of life, if it developed on Mars. In Jezero crater, we see signs of clay minerals having been transported in to the lake, and we also see carbonate minerals that would have precipitated in the lake. On Earth, these kinds of minerals occurring in relatively low-energy sedimentary delta environments can preserve organic matter. So if life ever developed on Mars and occurred in Jezero crater or its watershed, the delta deposits could potentially preserve it.

Outside of potential organic matter preservation, investigating Jezero geology could also help us put limits on how old the surface of Mars is. The crater floor appears to contain volcanic lava flows. One of the objectives of the Mars 2020 rover is to cache samples for their eventual return to Earth. If this mission succeeds and we are able to return samples, we could use radiometric dating to determine the absolute age of those lava flows. That, in turn, would allow us to pin one point in Mars' geologic history to a specific age and inform us about the maximum and minimum absolute ages of other terrains that pre- and postdate the lava flows on the crater floor.

Columbia Hills

Site location: 14.5478S, 175.6255E, -1930m elevation, ellipse 9.6 x 8.7 km

Detailed fact sheet about Columbia Hills (PDF)

The Mars Exploration Rover Spirit explored the Columbia Hills during its seven-year mission, from 2004 to 2010. Spirit's science team found a variety of geologic units along the traverse near the Columbia Hills within Gusev crater, including one volcanic unit and one potentially hydrothermal region. The landing site is volcanic, similar in composition to the Columbia River Flood Basalts in the U.S.'s Washington state. The main potential landing area of interest for Mars 2020 is a proposed hydrothermal site, which may have once been like some of the hydrothermal regions within Yellowstone National Park. The rover would have to land on the flat-lying volcanic rocks and trek about five kilometers to the interesting hydrothermal deposits. The drive could take from three to six months because Mars rovers move at only a fraction of average human walking speed, and available power usually limits their drives to one to two hours per day.