IN DEPTH: Zeroing in on Mars

Dec. 28, 2006 — Scientists ended 2006 with the loss of an old friend at Mars, but the defunct probe left behind a sweet legacy.

Among the thousands of pictures taken by the Mars Global Surveyor spacecraft before its demise were a handful that captured a subtle but startling change: frosty looking white streaks in gullies that just a few years earlier showed only craggy rock.

The obvious interpretation was a mind-blower: liquid water, mostly likely bound in some sort of sludge, making a brief but convincing appearance on the planet’s surface, not billions or millions of years ago, but in present day.

"The evidence, I would say, makes it almost completely obvious that we have seen examples of flowing water on Mars," said NASA administrator Michael Griffin. "The images were vastly different and they were vastly different in a way that almost can only be made by running water."

"It validates a long-standing scientific hypothesis about Mars that underneath the surface might be extensive areas of permafrost which occasionally, through one mechanism or another, turn briefly into flowing liquid water," Griffin added.

The prospect of present-day liquid water cuts to the heart of what has become the holy grail of planetary exploration: to determine if life ever took hold any place besides Earth.

"The presence of liquid water on Mars has profound implications for the question of life not only in the past, but perhaps even today," said Ed Weiler, a long-time NASA scientist and program manager who now heads the Goddard Space Flight Center in Greenbelt, Md.

Added Michael Malin, lead scientist on the Global Surveyor camera team, "If there is liquid water on Mars then theoretically it improves the possibility, the chances that there might be life on Mars."

Scientists spent years piecing together Global Surveyors' puzzle, which proved so profound as to completely overshadow news of the probe's mysterious failure two months ago after a decade of productive work at Mars.

With a new, sharper-eyed robotic sentry already in position to take over as chief Mars photographer, scientists have had little time to mourn. Imaging Martian gullies, in hopes of spotting actual sediments from water flows, has become a key part of Mars Reconnaissance Orbiter’s science agenda.

"We've moved it up the priority list," said MRO science team member Roger Phillips, with Washington University in St. Louis, Mo.

MRO is also tasked with finding a landing spot for Phoenix, a sophisticated Mars probe scheduled for launch in August. Phoenix is expected to touch down in May 2008 in the northern polar region of Mars. The stationary lander will use a robotic arm to bore down into the icy soil and scoop up samples to analyze.

Phoenix’s suite of scientific gear includes tools to determine if microbes existed in the ice.

"We will be able to make a very accurate analysis of what promises to be some of Mars' more habitable terrain," said principal investigator Peter Smith, with the University of Arizona’s Lunar and Planetary Laboratory in Tucson.

Phoenix is to be the sixth spacecraft dispatched to the planet’s surface, two of which are still working.

The Mars Exploration Rovers Spirit and Opportunity, both years beyond their design lifetimes, are investigating opposite sites on Mars' equator for signs of past water.

Opportunity is beginning a study of a large crater near its landing site in Meridiani Planum, which showed evidence of a shallow salty ocean. Scientists hope Opportunity may be able to provide more clues about how widespread the surface water was and, most importantly, if it existed long enough for life to form.

Spirit is on high ground in the Columbia Hills of the Gusev Crater. It too has found water-altered minerals in the soil and rocks. The rovers, originally designed to last 90 days on the Martian surface, begin their third year of operations on Jan. 3. NASA has approved another round of mission extensions through September.

One of the key challenges facing scientists in 2007 will be to decide how the new evidence of surface water revealed in Global Surveyor’s images should be addressed in future missions. Once Phoenix is on its way, NASA will turn its attention to the Mars Science Laboratory, slated for launch in 2009.

MSL has wide berth because it will be able to land within a target area that is 12.4 miles (20 kilometers) in diameter, as high as 1.2 miles (two kilometers) from the planet's surface and anywhere up to about 60 degrees north or south of the equator.

In comparison, NASA had about 10 options for its 1997 Mars Pathfinder mission and about 150 contenders for Spirit and Opportunity landing sites.

"There are literally billions of potential landing sites," said NASA planetary scientist Matt Golombek.

"For the first time, we are being given the opportunity to really go anywhere on Mars."