Will NASA ever find life on Mars?

Tools of the trade
Both NASA's MSL and the European ExoMars rovers can explore the Martian surface more effectively than Phoenix, and the ExoMars rover will also carry a heavy duty drill to dig for biological gold. But both rovers still face the challenge of knowing where to look.

"We don't know what the recipe is for success, or the paradigm for preserving life on Mars if it ever evolved," said John Grotzinger, geologist and MSL project scientist. He emphasized that finding preserved organic material is no cinch, and pointed out the rarity of uncovering fossil records of early life on Earth.

The mega-rover MSL will scoop up dust and drill into rocks to test for organic building blocks of life such as carbon, hydrogen, nitrogen and oxygen. MSL will also carry a laser to vaporize rock samples and allow it to sift through the resulting dust.

Grotzinger and the MSL team aim to boost MSL's chances by choosing a landing site with a diverse environment, including areas with signs of water and minerals such as clay and sulfates that could preserve organic material.

ExoMars holds the additional promise of allowing scientists to dig deeper than ever before on Mars, and presents possibly the best chance of finding solid evidence of existing or past life. However, not knowing what lies beneath the Martian surface tempers optimism for finding life during the near-future missions.

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"I'm going to give the next two rovers a 50-50 chance," Storrie-Lombardi said. "Once we go deep it's a whole different game."

An additional instrument may improve the odds for MSL or ExoMars. Storrie-Lombardi worked with U.S. and U.K. researchers on a small laser that can make organic compounds glow fluorescent under its ultraviolet beam.

The laser probe could illuminate holes dug by ExoMars to see which areas glow the brightest. That would allow scientists to target those places for testing with more limited-supply wet chemistry tests, which mix soil and rock samples with water or other reagents to identify what building blocks of life might exist.

"If the team can show this is light and rugged enough, we will propose taking it to Mars," said Andrew Coates, planetary scientist and ExoMars investigator.

Slow but steady
When NASA's Viking mission reached Mars in 1976, the twin landers uncovered no traces of organic material in scooped-up Martian soil. A study later found that the tests used by the Viking landers even failed to detect organic material on Earth in places teeming with microbes.

Much has changed since then besides having more sensitive instruments. Scientists now know much more about the Martian environment and the likelier hiding holes for life, thanks to the long list of Mars missions leading up to Phoenix.

"Phoenix, Mars Science Lander, these all have a chance of discovering life," Jakosky said, "but that's not the goal of the missions."

NASA's incremental approach can appear frustratingly slow to even scientists. But Jakosky explained that each mission has made new and different discoveries that add to overall understanding of Mars as a system — and that helps narrow the search for life.

"Organics can be produced by non-biological processes, and indicators of life on Earth may not be indicators of life on Mars," Jakosky said. "In order to know how to interpret any measures we make, have to look at Mars as a system."

By contrast, Viking represented a shot in the dark without any of that understanding.

"We tried the cash in all your chips approach, and that was the Viking spacecraft," Jakosky said. "It was an incredibly naive, narrow-minded approach, and in hindsight there's no expectation it should have found life."

Bring it home
MSL and ExoMars should help clarify questions about where to find organic material and possibly life on Mars. However, robotic explorers can only provide test results and images to humans back on Earth, which leaves room open for debate about what exactly they have found.

"We might have to wait to bring a sample back or send a human there," Storrie-Lombardi noted. "It's sometimes difficult to come up with concrete evidence that everyone agrees on."

Getting a Mars sample back to Earth would mean scientists could examine the evidence with all the most recent instruments and technology available, instead of just the limited experiments that each Mars mission can carry.

Jakosky agreed that scientists are "probably not getting definitive answer until we bring a sample back," a possible but complicated mission proposal.

ExoMars includes plans that would test technology for such future sample-return missions, and MSL will similarly "take us a long way towards determining what are the favorable rocks to bring back," said Grotzinger on the MSL team.

For now, scientists remain cautious but hopeful about the question of life on Mars — and above all excited.

"I think it'd be stunning if we don't find evidence that there is life or was life in the past," Storrie-Lombardi said.

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