Despite the news of liquid water on Mars last week, professor of civil and environmental engineering and earth sciences Clive Neal said this is not a new discovery.
“They found water on Mars — well, we knew there was water. There had been water on Mars from the Mariner and Viking orbital images,“ Neal said Tuesday. “Quite frankly, what they found [last Monday was] reported in a paper in 2000.”
According to Neal, the first paper to reveal the presence of water on the planet identifies what are known as “RSLs”, or recurring slope lineae. RSLs are visible on Mars’ surface as dark streaks running down steep craters and mountains, and they appear when temperatures are high and disappear when it gets cold.
Neal said RSLs could actually be liquid water.
After observing the RSLs for several years, scientists started constructing a hypothetical Martian water cycle, Neal said.
“Water will come out of the subsurface, then it will flow for a little bit, then it will sublimate and go to the vapor phase or it will be absorbed into the subsurface,” he said. "It works kind of like a mountain stream — ice melts as temperatures rise, and small streams run down the slopes. With Mars, those streams, the RSLs, are likely sourced in underground ice, and when it gets cold, they either seep back beneath surface or evaporate into Mars’ thin atmosphere.”
According to a paper published last week in Nature Geoscience, until recently, the only evidence of this liquid water cycle was photographs of RSLs. That all changed last week, when a high-resolution camera on NASA’s Mars Reconnaisance Orbiter identified the presence of perchlorates on the Martian surface. Perchlorates are small hydrated salts that act as sponges to absorb liquid water, and scientists hypothesize that if perchlorates are found, liquid water nearby will almost always be found nearby.
Director of NASA’s planetary science division James L. Green said during last week’s news conference that Mars is not the dry, arid planet NASA thought in the past.
Rethinking Mars’ climate may mean rethinking Mars space missions, and that could mean sending astronauts. While that possibility is certainly being discussed, Neal said he is skeptical.
“You have a conundrum with humans going to Mars, because of planetary protection,” he said. “If we send them to Mars, can we ever bring them back?”
Neal said the issue is twofold — on one hand, humans cannot contaminate Mars with microbes from Earth, and on the other, they cannot have astronauts accidentally bringing back Martian bugs as potentially deadly souvenirs.
That raises a whole new question about life on Mars, Neal said. Liquid water is required to support life, and the fact that Mars has it makes it all the more likely that Mars is supporting something other than dust.
“It’s neat, we get liquid water on Mars now. That does increase the possibility for habitable environments for life — bug life, anyway,” Neal said. “There might be certain environments or niches where life, bacterial life, could still be abundant."
According to Neal, the next step is bringing samples back from Mars.
“That was the goal of the Mars program in the next decade, according to NASA’s planetary science division, was Mars sample return,” Neal said.
What has changed now is the kind of samples to bring back – with liquid water and the potential for life, the focus has shifted to bringing back samples of ice, of sediment around the RSLs and ideally of the perchlorates themselves, Neal said.
