Life may well lurk beneath the Martian surface today, but it'll be tough to detect without sending humans to the Red Planet, some experts say.
It could be a long time before robots are able to drill deep into the Martian underground, explore caves and investigate other potentially life-supporting habitats on the Red Planet. So if humanity wants to satisfy its curiosity about potential life on Mars anytime soon, it should work to get boots in the red dirt, advocates say.
"We might be lucky and confirm life with robots over the next one to two decades, but it's probably going to take people to do, literally, the heavy labor to be able to do it," said Chris Carberry, co-founder and executive director of Explore Mars, a nonprofit organization dedicated to human exploration of the Red Planet.
Most scientists think the frigid, dry and radiation-bombed Martian surface is unlikely to host life as we know it today. But conditions could be much more benign in underground environments such as caves or lava tubes, providing potential refuges for microbes.
"The subsurface is going to be radically different from the surface," astrobiologist and cave scientist Penny Boston, a professor at the New Mexico Institute of Mining and Technology, told SPACE.com late last year. "Every indication we have from caves of all different kinds all over this planet [Earth] shows that it doesn't take much separation vertically for a radically different environment."
Indeed, the Martian subsurface is known to harbor water ice, and several recent studies suggest that pockets of liquid water may exist beneath the red dirt as well. Here on Earth, life thrives pretty much anywhere liquid water is found, so the possibility of current Martian aquifers excites astrobiologists.
Adding to the intrigue, Carberry said, is the fact that several different ground-based and space-based instruments have detected small amounts of methane in Mars' air. The gas could be an indicator of Red Planet life, some researchers say, since 90 percent of Earth's methane is biologically derived.
Further, scientists think methane disappears rapidly from the Martian atmosphere, meaning any of the stuff swirling there today was likely produced in the recent past.
"There is a strong, growing body of evidence that there could be subsurface life on Mars," Carberry told SPACE.com. "However, we may not be able to confirm that unless we send people."
Exploring the Martian underground
Carberry lauded the work of Red Planet robots such as the car-size Curiosity rover, whose mission team recently determined that Mars could have supported microbial life billions of years ago.
But he said the search for extant Martian life is really a job for human explorers, at least for the near future. Current robots just aren't capable of drilling several meters beneath the Red Planet's surface, for example, or rappelling down into a lava tube by themselves.
"There are so many different things, so many complicated processes, that a human could do as long as they had a backup, a partner, to help them," Carberry said, "but robots can't — or if they can, it's going to take them an awful long time."
"The unfortunate truth is that most things our rovers can do in a perfect sol [Martian day], a human explorer on the scene could do in less than a minute," Squyres wrote in his 2005 book "Roving Mars: Spirit, Opportunity, and the Exploration of the Red Planet."
Protecting potential Mars life
Sending people to search for Martian life would raise some ethical concerns, however.
Every astronaut who lands on the Red Planet will bring with him or her a swarming mass of 100 trillion microbes — the diverse "microbiome" that has evolved with humans for eons and provides a number of services, from aiding food digestion to keeping pathogenic bacteria at bay.
Some of these microbes would invariably jump ship on Mars, potentially swamping or destroying the organisms their human hosts were sent to detect.
"When you send humans to the next planet, you will always contaminate that planet, because you cannot sterilize a human like you can sterilize [NASA's 1970s-era] Viking spacecraft," Bas Lansdorp, co-founder and CEO of the Netherlands-based nonprofit Mars One, said during a news conference Monday (April 22).
Mars One aims to land four humans on the Red Planet in 2023 to jump-start a permanent colony there. The organization does not plan on aggressively seeking out Mars life; rather, it will try to put its settlement in a spot that minimizes the risks to potential indigenous organisms, Lansdorp said.
Scientists and space agencies around the world are well aware of the planetary protection issue. In 2008, the Committee on Space Research (COSPAR) drew up a set of guidelines that seeks to safeguard Earth from "back contamination" from Mars, and to protect potential Red Planet life from an interplanetary invasion as well.
The COSPAR guidelines — which NASA and the European Space Agency, among others, are committed to follow — advise steering clear of gullies, possible geothermal sites and other "special regions" on Mars where Earth life might be able to get a foothold.
Such restrictions could make a manned life hunt difficult, since these places are also the most likely to harbor Red Planet life.
Carberry said future manned missions should take strict precautions to minimize their impact on the Red Planet and any potential indigenous lifeforms. But he doesn't think planetary protection concerns should keep humanity away from the Red Planet entirely.
"That's not a good reason not to go," Carberry said. "If we used that rationale for not going to Mars, we pretty much could eliminate all human exploration anywhere from now on."
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