The planet today has almost no atmosphere, no liquid water, and its surface is bombarded by intense radiation. “We now think the likelihood of life existing on its surface is slim to non-existent,” said Matthew Golombek, of NASA’s Jet Propulsion Laboratory in Pasadena, California.
American rocket engineers have told NASA they want the agency to “dream big” to ensure their new robot rover, scheduled for launch in 2020, visits a maximum number of sites to increase chances of uncovering signs of ancient life on Mars.
Rock samples – hopefully bearing fossils – would then be left in caches on the Martian surface, to be collected several years later and returned to Earth in a complex series of robot “sample return” missions costing more than $10bn.
“The community prefers a mega-mission,” said Bethany Ehlmann, a planetary scientist at the California Institute of Technology and a member of the Mars 2020 science team, quoted in Nature this month. “If we are going to do a sample return, it has to be a sample cache for the ages.”
US scientists are concentrating on rocks formed in watery environments billions of years ago, when the planet was much more Earthlike, reports Robin McKie at The Guardian. These rocks, as they formed, would have preserved remnants of any life that flourished before the planet’s atmosphere evaporated and its surface water boiled off.
The next Mars rover will drill into promising sediments, collect samples and place them in test tubes that will then be dumped in caches. The original proposal was to create one cache but, at a meeting this month, scientists pressed for several to be created.
Three sites close to each other were pinpointed as being particularly promising and were voted as favorites among scientists at the meeting in Glendale, California: these are known as Jezero crater, Northeast Syrtis and Midway. “we should go where the action was,” Ehlmann says.
Midway and Northeast Syrtis both hail from a time, some 4 billion years ago, when Mars was warmer and wetter. Surveys from orbit suggest the sites harbor rocks that formed underground in the presence of water and iron, a potential food for microbes. The rocks, exposed on the flanks of mesas, include a layer of carbonate deposits that many scientists believe were formed by underground mineral springs. Sheltered from a harsh surface environment, these springs would have been hospitable to life, Ehlmann says.
Jezero (image at top of page) and Northeast Syrtis, hold evidence of a fossilized river delta and mineral springs, both promising environments for ancient life. Scientists yearn to visit both, but they are 37 kilometers apart—much farther than any Martian rover has traveled except Opportunity.
Jezero and Midway are thought to be most useful. However, the two sites are 17 miles apart. NASA’s most advanced robot, Curiosity – a sister craft to the forthcoming rover – has travelled only 12 miles since it landed in 2012. “Creating two caches at Jezero and Midway would push our technology to the very limits,” Golombek admitted. “On the other hand, we need to make sure we get the best possible samples. We are going to have to work hard on this.”
“River and lake deposits on Earth are some of the best preservers of biologic signatures,” said Tim Goudge, at Brown. “At Jezero, you’re gathering all this material from this huge watershed and dumping into one place. So if there perhaps was any biologic or organic material in the watershed, you might have transported some of that to the basin.”
The false-color topographic map shown above (blue marks low elevations) shows the area around Jezero Crater. Flowing water would have gathered any biologic or organic material from a wide area and deposited it at the crater, making it a logical landing site for a future Mars rover mission.
“We can say that this one really well-exposed location makes a strong case for at least two periods of water-related activity in Mars’ history,” said Goudge. “That tells us something really interesting about how early Mars operated.”
The ancient lake at Jezero crater was first identified in 2005 by Caleb Fassett, a professor at Mount Holyoke College. Fassett identified two channels on the northern and western sides of the crater that appear to have supplied it with water. That water eventually overtopped the crater wall on the southern side and flowed out through a third large channel. It’s not clear how long the system was active, but seems to have dried out around 3.5 to 3.8 billion years ago.
A delta-like fan at the western edge of Jezero Crater marks an area where flowing water would have entered the lake-filled crater and deposited clay minerals transported from the surrounding watershed.
Around 2026, Nasa plans to launch a follow-up mission that would land a rocket launcher and new robot craft, called Fetch Rover, on Mars. Fetch Rover will gather up the caches and deliver them back to the rocket, which will then blast the samples into orbit round Mars. There it will rendezvous with an orbiter to carry the samples back to Earth.
“We will have the strictest quarantine conditions enforced when we collect and store those samples,” said Golombek. “It will be worth the effort and expense, however. This is going to be our best chance of finding out if life evolved independently on another world and that life here is not just a lucky accident.”
The Daily Galaxy via and The Guardian and Brown University
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