Curiosity in Mars

 This week's arrival of NASA's Mars rover Curiosity set the stage for a potentially game-changing quest to learn whether the planet most like Earth ever had a shot at developing life, but follow-up missions exist only on drawing boards.

The United States had planned to team up with Europe on a trio of missions beginning in 2016 that would culminate in the return of Mars soil and rock samples to Earth, an endeavor the National Research Council considers its top priority in planetary science for the next decade.

Citing budget concerns, the Obama administration terminated NASA's participation in Europe's ExoMars program earlier this year, spurring the U.S. space agency to re-examine its options before another flight opportunity comes and goes. Earth and Mars favorably align for launches about every 26 months.

The situation is complicated by massive budget overruns in the $2.5-billion Curiosity mission, intended to determine if Mars could now or ever have supported microbial life, and in the $8 billion James Webb Space Telescope, a successor to the Hubble observatory.

Those overruns are partly to blame for leaving Mars exploration short of the multibillion-dollar commitment needed for another "flagship" mission of the scale it would take to fetch rocks and soil from the Red Planet and bring them home.

A NASA report due for release this month is expected to outline lower-cost alternatives for Mars missions that could launch in 2018 and 2020.

A second rover mission to follow up on Curiosity's findings or to explore one of three other candidate landing sites originally identified for Curiosity would be "the next logical step," said NASA's Mars exploration program chief, Doug McCuistion. But he doubts he will have the money for it.

Although unlikely to draw a crowd to New York's Times Square like Curiosity's spectacular landing did, a new orbiting satellite to detect and analyze minerals or peer beneath the planet's surface with infrared eyes would help scientists zero in on the best place for an eventual sample-return mission. It also would provide a welcome backup communications link for Curiosity and any future landers and rovers, scientists say.

PLAN B

"We have to address the overall goal that the (National Research Council) decadal survey set for Mars exploration, which is sample return," NASA's chief Mars scientist, Michael Meyer, told Reuters. "I suspect there are other things that we may do on Mars, but if they don't help sample return they may be viewed as a non-starter."

Searching for evidence of life or its key ingredients on Mars, believed to have once been warmer and covered with water like Earth, is not the only rationale for a sample-return mission.

Detailed analysis of Martian minerals also could tell the story of what happened to the planet itself and why it ended up the cold, dry and acidic desert that exists today.

"Finding life is not why most of the science community is interested in sample return. There's a reasonable proportion who figure, ‘Well, we don't see life on Mars now, so it's probably not there, and that if the only payoff is finding life you're wasting your time.' That's some of the science community," Meyer said.

"The fact that you could look at all the information that's in your samples, determine what environments it saw, is tremendous. There's a lot of things that would really boost our understanding that have nothing to do with life," he said.

VIKING, REVISITED

Fresh off the heady days of its Apollo moon missions, NASA took a stab at a direct search for life on Mars with its Viking probes in the 1970s.

Most scientists chalked up the results as a big negative, and exploration of the fourth planet closest to the sun slipped into a 20-year hiatus.

Later, encouraged by discoveries of life in extreme environments on Earth, scientists returned to Mars with orbiters and a pair of small surface rovers, Spirit and Opportunity, to consider a tangential question: Since life on Earth depends on water, where did Mars' water go?

Rather than focus on direct detection of living organisms or fossilized remnants, NASA's strategy has been to "follow the water," by looking for particular rocks and features that form when water is present.

Curiosity's landing site in Gale Crater, located in the southern hemisphere near the planet's equator, was selected in part because it is one of the lowest places on the planet.

"Water flows downhill, so we chose to go to a low place," said John Grotzinger, a California Institute of Technology geologist who is the mission's lead scientist.

At the center of the crater is a 3-mile- (5-kilometer-) high tower of layered rock, named Mount Sharp, which is believed to have formed from the remains of sediment that once filled the impact basin. During its planned two-year mission, the rover is expected to ascend Mount Sharp, analyzing and dating its rocks and soil and looking for niches that may once have supported, and perhaps still host, life.

That information, in turn, will sharpen planet-wide analysis of Mars that is obtained from orbital imagery and sensors.

"We're going to get some ground truth to figure out the most interesting places to do sample return," said NASA's associate administrator for science, John Grunsfeld, a former astronaut.

The only other Mars mission in NASA's pipeline at the moment is an atmospheric probe scheduled to launch at the end of next year. The agency plans to submit its follow-up Mars proposals to the White House in September, in time for the fiscal year that begins in October 2013.

 The Mars rover Curiosity successfully raised the mast that holds many of its instruments Wednesday, giving controllers a view of the ground scorched by the rockets that deposited it on the surface.

The car-sized rover landed on Mars early Monday after a harrowing descent that climaxed with its being lowered by a "skycrane" that hovered over the landing site. Cameras mounted on Curiosity's remote sensing mast beamed back fresh images of the site once the column was raised into position, giving NASA a view of the roughly half-meter (19-inch) "scour marks" from the rocket exhaust.

Those gouges are giving mission controllers an unexpectedly early view of the bedrock beneath the surface of Gale Crater, said John Grotzinger, a Curiosity project scientist at the California Institute of Technology.

"Apparently, there is a harder, rockier material beneath this veneer of gravel and pebbles, and obviously there's some impact ejecta," Grotzinger told reporters at NASA's Jet Propulsion Laboratory, where controllers operate the rover. While Curiosity isn't yet ready to start driving around, "Here we've already got an exploration hole drilled for us," Grotzinger said The mission of the mobile science laboratory is to determine whether Mars ever had an environment capable of supporting life. Its prime target is the 18,000-foot (5,500-meter) peak at the center of Gale Crater, Mount Sharp, where scientists hope to get a layer-by-layer look at the history of the planet.

Grotzinger said so far, the landscape looks somewhat familiar.

"The thing that really struck the science team about this image is that you would really be forgiven for thinking that NASA was trying to pull a fast one on you and we actually put a rover out in the Mojave Desert and took a picture -- a little L.A. smog coming in there," he said.

Controllers are still activating Curiosity's instrument package, and all antennas that will beam back data to JPL "work perfectly," mission manager Jennifer Trosper said Wednesday. The onboard weather monitoring unit has turned out to be "completely healthy" following a brief glitch reported Tuesday. The high-bandwidth antenna that aims back at Earth is beaming back "lots and lots of data" and the rover is expected to capture a color panorama of its surroundings on Thursday, she said.

"There are going to be some amazing images from that," Trosper said.

Vandi Tompkins, one of Curiosity's operators, said images like those beamed back so far will be used to program the rover's movements when it gets under way.

Because of the time needed for a radio signal from Earth to reach the rover -- about 14 minutes at Mars' current position -- "We don't command the rover with a joystick or a steering wheel in real time," Tompkins said. "If we were to do that, by the time we would see we were at the edge of a cliff, the rover would have driven off of it."

Instead, operators use the photos to develop a plan for the next day's operations and transmit it to the rover, which carries it out and sends back the results.

Curiosity will start its third full martian day, or sol, on Thursday. A sol is about 40 minutes longer than a day on Earth.

The rover is supposed to run for two years, but a previous rover, Opportunity, has been working on Mars since 2004 -- well beyond the three months NASA planned. Opportunity's sister rover, Spirit, ran from 2004 to 2010.