Mars 2020: Where We'll Look for Alien Life: Photos

Scientists are meeting this week to discuss landing sites for NASA’s next Mars rover, that will look for past life and stash rocky samples for Earth-return. These are some of the landing sites under consideration.

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Scientists are meeting this week to discuss landing sites for NASA’s next Mars rover, an ambitious mission that not only will attempt to look for past life on Mars, but also stash samples drilled out from rocks for a future rover to retrieve and fly back to Earth for analysis. The point of the meeting is to discuss the current top candidate landing sites, though the list likely will change as new images and science data come in from satellites orbiting Mars and from NASA’s ongoing Curiosity and Opportunity rover missions.

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The new mission, still generically referred to as Mars 2020, is due to blast off in July or August 2020 and land itself in February 2021 using a heat shield, parachutes and Curiosity’s “skycrane” tethered descent system (pictured here). Engineers also are working to develop a “terrain recognition navigation” system that would allow the descending spacecraft to take pictures and match them with imagery stored in its computer for more precise steering. That system could make many more potential landing sites safe for touchdown. Another concern is how fast the rover could traverse the surface so that it can meet its mission goals, including drilling and cache 20 samples, in one Martian year, or 668 Earth days.)

Here’s a look at some of the leading landing site contenders.

Tucked between a large volcano and an ancient impact basin is a region known as Nili Fossae, which is marked by wide, curved troughs cutting about 1,600 feet into the Martian crust. Nili Fossae is replete with clay-rich rocks, which form in the presence of water and which may be key to finding preserved organics. Nili Fossae was a top candidate for NASA’s ongoing Curiosity mission, but the site was cut due to engineering concerns.

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Scientists believe water once flowed and pooled inside an ancient crater known as Jezero, located near the Martian equator. The water streamed in from the northern and western sides of the crater, now marked by dried out channels, and eventually overflowed the crater’s southern wall, creating a third channel. Scientists do not know how long the water existed, though they do think there were at least two separate water events before the area dried out between 3.5 billion and 3.8 billion years ago. Chemical data collected by Mars orbiters show Jezero has clay and carbonate minerals that were altered by water. If life evolved during the time when Jezero was flush with water, it may be preserved in the sediments.

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Ancient exposed bedrock and a diverse collection of hydratated minerals got this site a spot on the Mars 2020 candidate landing list. The targeted zone is located in the northeast part of Syrtis Major, a huge shield volcano and near the northwest rim of the giant impact basin Isidis Planitia.

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Scientists took a long, hard look at 100-mile wide Holden Crater before deciding to send the Curiosity rover to Gale Crater instead for a mission to assess if Mars ever had all the ingredients necessary for life. That goal was met less than seven months after the rover’s Aug. 3, 2012, touchdown. Holden, along with Eberswalde Crater and Mawrth Vallis, made to the short list of Curiosity candidate landing sites and remains of interest to scientists on the follow-on Mars 2020 mission to actually look for signs of ancient life and cache samples for an eventual return to Earth.

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Holden Crater was once believed to have been “Holden Lake.” It contains two layers of sediments, the lower of which is believed to have formed in a large lake. The upper layer likely formed when water pooled in an area to the south known as Uzboi Vallis broke through Holdin’s rim. The current must have been strong, capable of transporting boulders dozens of feet in diameter. Within Holden’s ancient basin are numerous smaller craters, many of which are filled with sediments.

The widest segment of the massive Valles Marineris canyon system is known as Melas Chasma, which cuts through layered deposits believed to be sediments from an ancient lake. Melas has hydrated sulfates and other minerals transformed by water. The southwest region contains fan-shaped structures, indicating the lake’s water level fluctuated. Another attraction is the site’s proximity to seasonal features, known as recurring slope linea, or RSL, which may be signs of present day briny water near the surface, which potentially could be explored during a mission extension.

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