Mars 2008: A Red Planet Odyssey

Mars 2008: A Red Planet Odyssey

Mars Global Surveyor

This artist rendering shows the Mars Global Surveyor in orbit around the Red Planet. The Surveyor is just one of a host of instruments studying Mars for signs of water and the organic building blocks necessary for life.

At the tail of 2007, the intrepid robotic explorer Spirit was beating a path to a safe spot to spend the Martian winter. It was a hard year, and the small, six-wheeled rover still bears the scars of a planet-wide dust storm that nearly ended its mission.

Spirit and a twin named Opportunity have been pawing the dead Mars terrain for signs of past water, a key factor in scientists' ongoing quest to determine if Earth's neighbor ever hosted life.

The dust storm left Spirit so caked with debris that sunlight has a hard time getting through to the solar power cells that charge the rover's batteries. The past three weeks were particularly tense because the sun is not rising very high in the sky as the planet's southern hemisphere pivots into winter.

Still Going, and Going

But Spirit, which has already defied the odds, pulled through again, settling onto a northern-facing slope of a rock formation known as Home Plate in Gusev Crater. That it continues to operate at all, four years after arriving on Mars for what was designed to be a three-month mission, is most surprising.

Spirit's prowess has been matched by sister rover Opportunity, which is exploring a crater halfway around the planet. The dust storm shut it down for weeks as well, but Opportunity recovered quicker thanks to brisk winds that instead of depositing more sand blew its solar panels clean.

"The fact that these two rovers are going on their fourth year is amazing," said Mars researcher Ray Arvidson with Washington University in St. Louis.

Both rovers found mineralogical evidence that Mars had water on or near its surface at some point in its past. They will continue to pry out secrets even as scientists prepare for their first direct look at what remains of the planet's water today.

On May 25, a new probe named Phoenix is due to touch down on Mars' unexplored north pole. Its landing spot has been carefully selected and timed to coincide with the seasonal spring thaw. Scientists are counting on scratching through the ground cover and finding what may be a thick layer of water ice beneath the frozen surface.

"The first major discovery we think we'll see is ice," said Arvidson, a Phoenix co-investigator. After that, he added, "we don't know what we're going to find."

Phoenix will bake bits of Martian ice in tiny ovens to determine the isotopic composition of the water, information scientists can use to learn how recently the water was locked into the ground. If the isotopic ratios are similar to atmospheric composition, the water likely was a fairly recent phenomenon in a geologic sense, a mere 100,000 years old or so.

But if the ice samples show a disequilibrium with atmospheric measurements, then the water may be ancient, leftover remains of a long-vanished sea.

Either scenario, however, would reveal new details of Mars' evolution.

"We've never actually sampled the ice. We've never been that far north," Arvidson said.

Phoenix's science instruments will also hunt for organic molecules in the ice and soil. Organics, like water, are believed to be key for life to evolve.

"We're not going to have life or conditions suitable to have life unless we can make organic compounds and conserve them," Arvidson said.

Bird's Eye View

In addition to the surface robots, Mars will be studied from on high as well. Three orbiters -- Mars Odyssey, Mars Reconnaissance Orbiter and the European Space Agency's Mars Express -- are operating to photograph, map and chemically analyze the planet from the vantage point of space.

In addition to geologic signs of water, such as dried channels and riverbeds, the orbiters have instruments to find minerals associated with the presence of water, such as clays. The information is helping scientists hone in on potential habitats for past or present-day life and lay the foundations for a sample return mission around 2020.

In 2008, NASA will be narrowing down or even selecting a landing site for a sophisticated rover called Mars Science Laboratory that will analyze rocks and soil for signs of organic matter and environmental conditions suitable for life. MSL's launch is scheduled for 2009.

Also in 2008, NASA will select an atmospheric monitoring probe, which may be able to pinpoint areas on the planet's surface that are emitting methane, a chemical, which on Earth, has strong associations with organic matter and life.

"We're taking steps to efficiently explore this planet," Arvidson said. "By the end of the next decade, we'll have a much better understanding of the overall evolution of Mars and the role of water. If we're lucky, we may have evidence of past life or life today."