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How the hunt for Mars life evolved

NASA

In this artist's conception, Mars astronauts come upon one of the Viking landers that touched down in 1976.




The quest to learn about life on Mars has been lowering its sights for the past century, but researchers think they finally have the right strategy for addressing the key mysteries surrounding the Red Planet: Were the conditions right for living things to arise on Mars? And if so, what happened?

The romantic vision of Mars that many folks held onto in the early 20th century is on full display in Hollywood's 3-D blockbuster, "John Carter," which makes its debut Friday. In the movie, a visitor from Earth journeys along Mars' deserts and rivers, encountering green-skinned aliens, airship-riding warriors and, of course, a fetchingly clad Martian princess.

In August, which is probably around the time that "John Carter" comes out on DVD, the real-life Mars will take center stage. NASA's car-sized Curiosity rover is due to touch down at the end of a rocket-powered crane and become the latest robotic visitor from Earth. It will take pictures, drill into rocks, scoop up soil and perform chemical tests. If those tests match the science team's wildest dreams, the $2.5 billion mission will reveal ... a smattering of organic molecules.


NASA

Dave Beaty is chief scientist for the Mars Exploration Directorate at NASA's Jet Propulsion Laboratory.

"We want to find places that have high potential for habitability and high potential for preservation," David Beaty, chief scientist for the Mars Exploration Directorate at NASA's Jet Propulsion Laboratory, told me. "The actual test for life would be a subsequent mission."

Beaty will discuss the 21st-century plan for exploring Mars at 9 p.m. ET (6 p.m. PT) on Wednesday as my guest on "Virtually Speaking Science," an hourlong talk show that airs online as well as in the Second Life virtual world. Please join us by clicking onto BlogTalkRadio or teleporting into our Second Life auditorium. If you just can't make it, you can download the podcast after the show via BlogTalkRadio or iTunes.

How times have changed
NASA's expectations for the Curiosity rover mission — also known as Mars Science Laboratory, or MSL — are far less ambitious than the expectations that were common in the late 1800s, when millionaire astronomer Percival Lowell thought he saw evidence of a canal-building civilization on the Red Planet. The "canals" turned out to be visual illusions, and they weren't the last illusions surrounding the search for life on Mars. In the 1950s, the most famous rocket scientist of the age, Wernher von Braun, declared that a quarter of the Red Planet was "covered with a sort of plant life that our biological knowledge cannot quite encompass."

Such illusions were shattered once spacecraft came close enough to take pictures of Mars' magnificent desolation, starting with the Mariner 4 in 1964. Scientists saw a cold, dry world, with no verifiable signs of life on the surface. The Viking landers detected hints of organic activity, but not enough evidence to resolve the uncertainty. Since then, no additional evidence has come to light.

"Virtually every mission to the surface of Mars provides no evidence for anything," Caltech geologist John Grotzinger, project scientist for the Mars Science Laboratory mission, told me. "We don't expect to see any evidence for anything that might represent macroscopic life. At this point, we understand why that is. With reference to our own planet, if you go to extreme environments on Earth, places like Antarctica ... the only things that you would really ever see in these extreme places are microorganisms or other simple organisms, like lichens. We're not asking something special of Mars, we're just conditioning our expectations based on analogs to extreme environments here on Earth.

"You put deserts and extreme cold together, and you're not kidding anybody," he said. "You know you're looking for something that's probably going to be very small and highly specialized, with adaptation to an extreme environment."

Best places on Mars
Before they search seriously for that kind of life, scientists have to figure out the best places to look. That's what the MSL mission is all about. Grotzinger, Beaty and other members of NASA's Mars science team think the rover's destination in Gale Crater could be a promising place to sample billions of years' worth of geological layers. Rather than looking exclusively for present-day life, MSL's scientists will be hunting for chemical indicators that point to potential habitability as well as the prospects for preserving the traces of past life.

Scientists suspect that Martian surface may not be the best place to find those chemical indicators, due to the exposure to harsh radiation and oxidation. But if Curiosity can drill or dig a little deeper, it should have a better chance of finding intact amino acids and other chemicals that have been linked to life.

"If MSL were to make a pretty good discovery ... that may be enough to cause a subsequent mission to go back to that exact spot," Beaty said. But even if Curiosity doesn't hit a home run, the observations made in Gale Crater should provide enough geological diversity to give scientists a better sense of where future life-seeking probes should be sent.

Tough times ... and tough questions
Right now, NASA's Mars exploration program is going through tough budgetary times, and it's not yet clear how those future missions will be laid out. But Beaty is confident that NASA will continue to send robots to the Red Planet, with humans eventually following in their wheel tracks.

"Mars is widely thought to be the ultimate destination, at least for the foreseeable future," he said. "It may not be the next destination. We may have to go some other place first — to the moon, or a near-Earth object — to develop the experience to go onward to Mars. But I think the current view of the strategy is that those things would be way points on the way to Mars, and Mars is the object of greatest interest."

The big reason for that interest has a lot in common with the reason why Percival Lowell, Edgar Rice Burroughs and others looked so longingly at the Red Planet a century ago.

"The thing that's fascinating about Mars is that the period during which the planet as a whole was habitable was such a narrow window that opened early in its history, say, from 4.2 billion years ago," Beaty said. "There's evidence of channels and valleys and clay minerals, but then somehow the water was lost. Where did the water go?

"If Mars was able to establish life during the period when water was there, did it find a refuge — for example, in the deep subsurface — or did it just die out? ... And if Mars didn't have life, an equally important question is, why not? We have to know that, too. If it had all the right conditions, and Earth developed life while Mars didn't, what was different?"

To delve into these questions and other Martian mysteries, tune into "Virtually Speaking Science."

Join us at 9 p.m. ET Wednesday on "Virtually Speaking Science," which is broadcast on BlogTalkRadio and in the Second Life virtual world at the MICA Small Auditorium at Stella Nova. Many thanks to the Meta Institute for Computational Astrophysics for co-sponsoring the Second Life event. The hourlong show will be archived on BlogTalkRadio and iTunes. Check out these other podcasts from "VSScience":


This is the second of a two-part series about Mars in fact and fiction. For the fictional side of things, check out my interview with "John Carter" film director Andrew Stanton.

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.