Peter H. Smith, a scientist with the university’s Lunar and Planetary Laboratory and the mission’s principal investigator, is the first author of “H₂O at the Phoenix Landing Site” in Science. Smith and his group of scientists and students used the lander to investigate the role of water and ice on Mars, as well as the changing weather patterns.

The popular mission launched in early August 2007. In May 2008, it made its way to the martian surface, with its landing trajectory captured by the HiRISE camera onboard the Mars Reconnaissance Orbiter.

For the next 5 months, the University of Arizona’s Science Operations Center clattered with researchers gearing themselves to follow the martian diurnal phases, which are about 40 minutes longer than day and night on Earth and enough to throw off human sleep schedules in short order.

The landing site was an ejecta field. A comet or asteroid that crashed into the surface melted the ice below, which created a sheet of dust and water that flowed across a shallow valley. Smith said that event also covered any large rocks that could have interfered with the ability of the Phoenix to safely land.

Smith and his group found patterns in the ground near the lander, multisided shapes about 10 to 33 feet (3 to 10 meters) in size. The shapes are created when the surface contracts and the ice cracks. Sand fills in the cracks before the ice expands and buckles the surface to make the distinctive patterns.

Smith used the Phoenix Lander’s robotic arm to dig a series of trenches to expose subsurface ice and found that the ice in the centers of the polygons was fairly shallow, only a couple of inches deep.

“But in the troughs in between, we went down as much as 8 inches and never did find the ice underneath,” Smith said. “We weren’t able to dig further down because the robot arm was hitting against the side of the lander. It was not known ahead of time that there would be changes in the depth of the ice.

“We wanted to know the origin of the ice,” Smith continued. “It could have been the remnant of a larger polar ice cap that shrank; could have been a frozen ocean; could have been a snowfall frozen into the ground.

One of the surprises was finding perchlorate.

“Perchlorate was not predicted at this landing site, and nobody had it on their list of likely chemicals,” Smith said. “There was a very high concentration of it, higher than the salts we might have expected like sodium chloride [table salt]. As an oxidized state of chlorine, it has interesting properties including a strong affinity for water. On Earth, microbes use it as a chemical energy source.”

During the mission, Mars moved from summer to winter, giving Smith and others an unprecedented look at the planet’s changing weather patterns, including frost and snow.

“Frost was predicted, but snowfall was quite a welcome surprise,” Smith said. “In summer there was a lot of dust in the atmosphere. As we neared fall, the dust cleared, and all of a sudden there were water ice clouds forming at about 4 km [2.5 miles] above the surface. We could see the clouds scud by, moving through the camera field, and once we saw snow coming out of the bottom of a cloud. It was very exciting to watch the daily weather changes. No one has ever had this experience.”

Smith said there are clues that thin films of water modified the soil chemistry. Unlike Earth, Mars has an unstable spin axis, which currently is tilted at about 25° from vertical. Perhaps 5 millions years ago, he said, it was tilted much more, which would have exposed the north pole to larger amounts of sunlight and created warmer, wetter conditions during summer.

“During that previous climate, you would expect huge increase in the amounts of water vapor coming off the polar cap,” Smith said. “If the cap goes unstable, you can have as much as 300 times as much water in the atmosphere.”

It would have been enough for snowdrifts. On hot summer days, melting snow could have formed thin films of water.

Not enough for a lake or a river, but he said this could have been a time when damp soil provided a growth period for any microbes that learned to survive those long periods of dryness.

“Who knows? Evolution is a powerful force. If life ever started on Mars, there are niches where still it could survive.”

The new global digital elevation model of Earth was created from nearly 1.3 million individual stereo-pair images collected by the Japanese Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument aboard Terra. NASA and Japan’s Ministry of Economy, Trade and Industry (METI) developed the data set. It is available online to users everywhere at no cost.

“This is the most complete, consistent global digital elevation data yet made available to the world,” said Woody Turner, ASTER program scientist at NASA Headquarters in Washington. “This unique global set of data will serve users and researchers from a wide array of disciplines that need elevation and terrain information.”

According to Mike Abrams, ASTER science team leader at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, the new topographic information will be of value throughout the Earth sciences and has many practical applications. “ASTER’s accurate topographic data will be used for engineering, energy exploration, conserving natural resources, environmental management, public works design, firefighting, recreation, geology, and city planning, to name just a few areas,” Abrams said.

Previously, the most complete topographic set of data publicly available was from NASA’s Shuttle Radar Topography Mission. That mission mapped 80 percent of Earth’s landmass, between 60° north latitude and 57° south. The new ASTER data expands coverage to 99 percent, from 83° north latitude and 83° south. Each elevation measurement point in the new data is 98 feet (30 meters) apart.

The ASTER data fill in many of the voids in the shuttle mission’s data, such as in very steep terrains and in some deserts,” said Michael Kobrick, Shuttle Radar Topography Mission project scientist at JPL. “NASA is working to combine the ASTER data with that of the Shuttle Radar Topography Mission and other sources to produce an even better global topographic map.”

NASA and METI are jointly contributing the ASTER topographic data to the Group on Earth Observations, an international partnership headquartered at the World Meteorological Organization in Geneva, Switzerland, for use in its Global Earth Observation System of Systems. This “system of systems” is a collaborative, international effort to share and integrate Earth observation data from many different instruments and systems to help monitor and forecast global environmental changes.

NASA, METI, and the U.S. Geological Survey validated the data, with support from the U.S. National Geospatial-Intelligence Agency and other collaborators. The data will be distributed by NASA’s Land Processes Distributed Active Archive Center at the U.S. Geological Survey’s Earth Resources Observation and Science Data Center in Sioux Falls, South Dakota, and by METI’s Earth Remote Sensing Data Analysis Center in Tokyo.

ASTER is one of five Earth-observing instruments launched on Terra December 1999. ASTER acquires images from the visible to the thermal infrared wavelength region, with spatial resolutions ranging from about 50 to 300 feet (15 to 91 meters). A joint science team from the U.S. and Japan validates and calibrates the instrument and data products.

Matthew Balme from The Open University in the United Kingdom made the new discovery by studying detailed images of equatorial landforms that formed by melting of ice-rich soils. His work indicates that the martian surface experienced “freeze thaw” cycles as recently as 2 million years ago, and that Mars has not been locked in permafrost conditions for billions of years as had been thought previously.

The high-resolution images, which show a variety of interesting landforms, were taken with NASA’s High Resolution Imaging Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter (MRO).

“The features of this terrain were previously interpreted to be the result of volcanic processes,” Balme said. “The amazingly detailed images from HiRISE show that the features are caused instead by the expansion and contraction of ice and by thawing of ice-rich ground. This all suggests a very different climate to what we see today.”

All of the landforms observed are in an outflow channel, thought to have been active as recently as 2 million to 8 million years ago. Because the landforms exist within, and cut across, the pre-existing features of the channel, this suggests that they, too, were created within this timeframe.

The pictures show polygonally patterned surfaces, branched channels, blocky debris, and mound/cone structures. All of these features are similar to landforms on Earth typical of areas where permafrost terrain is melting.

“These observations demonstrate that there was not only ice near the martian equator in the last few million years, but also that the ice melted to form liquid water and then refroze,” Balme said. “And this probably happened for many cycles. Given that liquid water seems to be essential for life, these kinds of environments could be a great place to look for evidence of past life on Mars.”

“This new research has revealed more about Mars and provided fascinating evidence of geological process similar to Earth,” said Keith Mason, CEO of the Science and Technology Facilities Council (STFC). “The history of our neighboring planet, and the question of whether it has ever sustained life, has long fascinated man. Understanding current processes on the surface of Mars and the past and present role of climate, improves our knowledge of the planet’s history and the chances of one day detecting evidence for past or present life. Scientists are involved in a number of different Mars studies, which are helping to paint a full picture of this mysterious planet.”