Phoenix Mars Lander is silent, solar panels may have collapsed

"The Phoenix spacecraft succeeded in its investigations and exceeded its planned lifetime," said Fuk Li, manager of the Mars Exploration Program at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Although its work is finished, analysis of information from Phoenix's science activities will continue for some time to come."

Last week, NASA's Mars Odyssey orbiter flew over the Phoenix landing site 61 times during a final attempt to communicate with the lander. No transmission from the lander was detected. Phoenix also did not communicate during 150 flights in three earlier listening campaigns this year.

Earth-based research continues on discoveries Phoenix made during summer conditions at the far-northern site where it landed May 25, 2008. The solar-powered lander completed its three-month mission and kept working until sunlight waned two months later.

Phoenix was not designed to survive the dark, cold, icy winter. However, the slim possibility Phoenix survived could not be eliminated without listening for the lander after abundant sunshine returned.

An image of Phoenix taken this month by the High Resolution Imaging Science Experiment, or HiRISE, camera on board the Mars Reconnaissance Orbiter suggests the lander no longer casts shadows the way it did during its working lifetime.

"Before and after images are dramatically different," said Michael Mellon of the University of Colorado in Boulder, a science team member for both Phoenix and HiRISE. "The lander looks smaller, and only a portion of the difference can be explained by accumulation of dust on the lander, which makes its surfaces less distinguishable from surrounding ground."

The set of images above shows "before" and "after" images of Phoenix Mars Lander taken by HiRISE on Mars Reconnaissance Orbiter. Scientists are analyzing these images to better understand how the spacecraft may have endured its first Martian winter. The "before" image was taken on July 20, 2008 and the "after" image was taken on May 7, 2010. The new image of the Phoenix landing site is a close match to the season and illumination and viewing angles of some of the first HiRISE images acquired after the successful landing on May 25, 2008.

The large HiRISE image on the left was taken on July 20, 2008. The lander, heat shield, and backshell-plus-parachute are highlighted by inset boxes in that image. Smaller images on the right show side-by-side images of the lander, heat shield and backshell-plus-parachute in 2008 (before Martian winter) and 2010 (after Martian winter). Comparison of the two panels shows the lander, heat shield and backshell-plus-parachute now covered by dust. They lack the distinctive colors of the hardware or disturbances in pre-landing dust seen in 2008.

In the top right set of smaller "before Martian winter" and "after Martian winter" images of the lander, the 2008 lander image shows a very bright spot (from reflections) with relatively blue spots on either side corresponding to the clean circular solar panels. The shadows in that image consist of three overlapping dark circles, as shown by the schematic simulated image below the close-up lander images. In the 2010 image, where the illumination and viewing angles are within 1 degree of the 2008 image, scientists see a dark shadow that could be the lander body and eastern solar panel, but no shadow from the western solar panel. Because the reflection is no longer present on the dusty lander, the 2010 image should provide a better view of the shadow from the western array, but that shadow is absent.

Credit: NASA/JPL-Caltech/University of Arizona

Apparent changes in the shadows cast by the lander are consistent with predictions of how Phoenix could be damaged by harsh winter conditions. It was anticipated that the weight of a carbon-dioxide ice buildup could bend or break the lander's solar panels. Mellon calculated hundreds of pounds of ice probably coated the lander in mid-winter.

During its mission, Phoenix confirmed and examined patches of the widespread deposits of underground water ice detected by Odyssey and identified a mineral called calcium carbonate that suggested occasional presence of thawed water. The lander also found soil chemistry with significant implications for life and observed falling snow. The mission's biggest surprise was the discovery of perchlorate, an oxidizing chemical on Earth that is food for some microbes and potentially toxic for others.

"We found that the soil above the ice can act like a sponge, with perchlorate scavenging water from the atmosphere and holding on to it," said Peter Smith, Phoenix principal investigator at the University of Arizona in Tucson. "You can have a thin film layer of water capable of being a habitable environment. A micro-world at the scale of grains of soil -- that's where the action is."

The perchlorate results are shaping subsequent astrobiology research, as scientists investigate the implications of its antifreeze properties and potential use as an energy source by microbes. Discovery of the ice in the uppermost soil by Odyssey pointed the way for Phoenix. More recently, the Mars Reconnaissance Orbiter detected numerous ice deposits in middle latitudes at greater depth using radar and exposed on the surface by fresh impact craters.

"Ice-rich environments are an even bigger part of the planet than we thought," Smith said. "Somewhere in that vast region there are going to be places that are more habitable than others."

Source: Jet Propulsion Laboratory
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