Is there really water on Mars?

­While the sudden appearance of depository streaks thrilled many scientists, others began to question the flash-flood theory. Further analysis of at least one of the gullies suggested that its shape didn't match the way fast-moving water flows. The deposits' fingerlike shape suggested something granular and dry, like fine-grained sand, rushed through the valley [source: Lovett].

However, the shape of the gullies doesn't completely discount the possibility that there was liquid water involved. Even if the gullies were carved by sand, wet conditions could have initiated the landslide or a­ small amount of water could have mixed with dirt and sand to form slurry [source: Lovett].

The images that first got scientists speculating came from the High Resolution Imaging Science Experiment (HiRISE), a camera that can capture minute landscape details and geologic structures. It's one of six instruments that make up the Mars Reconnaissance Orbiter, which was launched with the mission to hunt for evidence of water. Scientists hope the mission will also clarify the climate and geology of the planet, but the orbiter's scientific payload focuses squarely on H₂­0.

By now, you've probably gathered that the orbiter isn't looking for some stray puddles or some body of water that scientists missed on previous surveys of the planet. Instead, the orbiter's cameras and spectrometers are searching for mineral deposits left by water. A sounder uses radar to find underground liquid reserves. Other cameras monitor clouds and dust storms. All the information from the Mars Reconnaissance Orbiter is relayed back to Earth through X-band and Ka-band radio waves that are picked up by the Deep Space Network antenna in Canberra, Australia.

­In the past, orbiting spacecraft have observed two groups of hydrated minerals on Mars: phyllosilicates, which formed 3.5 billion years ago when Martian water encountered rock, and hydrated sulfates, which formed 3 billion years ago due to evaporation. In 2008, however, the Mars Reconnaissance Orbiter discovered new hydrated minerals on the red planet in the form of hydrated silica, also known as opal. These newly discovered minerals formed when water was exposed to areas affected by meteorites or volcanic activity. These findings have shaved a billion years off previous estimates, indicating that Mars may have had liquid water as recent­ly as 2 billion years ago.

The orbiter also returned evidence of clay mineral deposits that only could have formed due to rock-fracture plumbing and water altering the landscape in early Martian history. Scientists think that flowing Martian groundwater formed these crevices in the planet's distant past.

­The Mars Reconnaissance Orbiter wasn't the only spy on the red planet over the last year. While the orbiter examined Mars from space, the Phoenix Mars Lander entered the planet's atmosphere to scope out conditions on the ground.

In May of 2008, the planet Mars received a rare visit from Earth. The Phoenix Mars Lander touched down in the previously unexplored far north to study Martian water. Such information could help scientists back home better judge if the planet could support life as we know it. After all, in the event of a manned mission to Mars, the presence of usable water could mean astronauts would have one less item to lug with them on their interplanetary trek.

­The lan­ding site was a prime area for exploration, since the northern polar region has plenty of water ice just beneath a very dry layer of soil. The Phoenix used its robotic arm to dig into the ground and collect samples of soil and ice, which were then analyzed for content. If that sounds like a piece of cake, bear in mind that it took earthbound scientists two full days just to successfully deploy the arm and prepare it for digging.

Despite the time and effort involved in every movement of the lander's limb, the Phoenix proved successful. It confirmed the presence of ice in the soil, glimpsed snow in the Martian sky and found evidence of both clay and calcium carbonate. This last discovery is particularly noteworthy since most clays and carbonates on Earth only form in the presence of liquid water.

The lander also discovered evidence of organic salts called perchlorates. Some experts argue that this last discovery kills the notion of life on Mars, as these salts rapidly decompose organic compounds. Still others hold out hope, pointing to some Earth species of bacteria that actually break down perchlorate. Might life on Mars have been similar to these bacteria?

That isn't the only new question scientists can look forward to tackling in future missions. The Phoenix also shed light on the red planet's humidity by using a spiky thermal and conductivity probe to detect rising and falling levels of water vapor in the air. Perplexingly enough, none of this moisture seems to collect on or in the thoroughly dry soil.

Originally scheduled for a three-month mission on the Martian surface, NASA renewed its mission twice and, even as cold October temperatures forced the scientists to begin shutting down the lander's systems, it was still sending readings back to Earth. While wintering on Mars most likely means frozen entombment in solid carbon dioxide, NASA hopes to revive the robotic lander when temperatures increase enough to allow all its systems to operate again and its solar panels to collect energy.

If Phoenix doesn't rise from the ashes in the Martian springtime, NASA will have to wait a few years before it lands a fresh set of electronic eyes on the planet's surface. The next mission to Mars is slated for a 2013 launch, when MAVEN, the Mars Atmosphere and Volatile Evolution spacecraft, makes its way to the red planet to study what might have happened to its atmosphere. The planet's atmosphere is currently so thin that exposed water can only remain stable in a solid or gaseous form. Scientists hope MAVEN will shed more light on Mars' wet past and if life in any form has ever existed on the planet. But for now, we know that there really is water on Mars. It's just not in the form that fills up your water glass.

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