Starship Asterisk*

NASA is once again listening for any signs that its Phoenix Mars Lander has resurrected itself after the long Martian winter, but so far, the frozen lander has remained silent.

The space agency is using its Mars Odyssey orbiter to scan for any beeps of life Phoenix may send in the off-chance it has survived the red planet's winter. The listening campaign is NASA's second for Phoenix and slated to last about a week.
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Odyssey conducted its first listen for signs of life from Phoenix in January. This second attempt began on Feb. 22 and will continue through Feb. 26 with 50 flights over the Phoenix site. A third campaign to check on whether Phoenix has revived itself is scheduled for April 5-9, when the sun will be continuously above the Martian horizon at the Phoenix site.

NASA's Phoenix Mars Lander showed no sign during February that it has revived itself after the northern Mars winter. NASA's Mars Odyssey orbiter will check again in early April.

The solar-powered Phoenix lander operated for two months longer than its planned three-month mission in the Martian arctic in 2008. It was not designed to withstand winter conditions. However, in case the return of abundant springtime sunlight to the site does revive Phoenix, Odyssey is conducting three periods of listening for a transmission that Phoenix is programmed to send if it is able. The second listening period, with 60 overflights of the Phoenix site from Feb. 22 to Feb. 26, produced the same result as the first listening period in January: no signal heard.

NASA's Mars Odyssey orbiter heard no signal from the Phoenix Mars Lander when it listened from orbit while passing over Phoenix 60 times last week.

Odyssey had also listened for a signal from Phoenix during periods in January and February. During the third campaign, April 5 through April 9, the sun stayed above the horizon continuously at the arctic site where Phoenix completed its mission in 2008.
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This was the last of our three planned Phoenix search campaigns. The Mars program will evaluate the results in hand to assess whether further action is warranted.

From May 17 to 21, NASA's Mars Odyssey orbiter will conduct a fourth and final campaign to check on whether the Phoenix Mars Lander has come back to life.

During that period, Odyssey will listen for a signal from Phoenix during 61 flights over the lander's site on far-northern Mars. The orbiter detected no transmission from the lander in earlier campaigns totaling 150 overflights in January, February and April.

In 2008, Phoenix completed its three-month mission studying Martian ice, soil and atmosphere. The lander worked for five months before reduced sunlight caused energy to become insufficient to keep the lander functioning. The solar-powered robot was not designed to survive through the dark and cold conditions of a Martian arctic winter. However, in case it did, NASA has used Odyssey to listen for the signals that Phoenix would transmit if abundant spring sunshine revived the lander.

Northern Mars will experience its maximum-sunshine day, the summer solstice, on May 12 (Eastern Time; May 13, Universal Time), so the sun will be higher in the sky above Phoenix during the fourth listening campaign than during any of the prior ones. Still, expectations of hearing from the lander remain low.

NASA's Phoenix Mars Lander has ended operations after repeated attempts to contact the spacecraft were unsuccessful. A new image transmitted by NASA's Mars Reconnaissance Orbiter shows signs of severe ice damage to the lander's solar panels.

"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."

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.

The latest HiRISE image appears to show that a solar panel of the Phoenix lander has collapsed.

HiRISE has been imaging the terrain around the landing site, including the Phoenix spacecraft itself, to study the seasonal changes that occur around this region. Phoenix landed on 25 May 2008 at 68 degrees North latitude during the Martian summer.

In the winter at this latitude the atmosphere and surface get so cold that carbon dioxide, which accounts for 95 percent of the gas in the Martian atmosphere, forms a frost on the surface as much as several decimeters (one or more feet) thick. This frost, also known as dry ice, blankets the entire northern landscape each winter, including any spacecraft that might be on the surface. In spring and summer this frost dissipates by sublimation, the process in which a solid ice evaporates directly to a gas without any melting.

This 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 25 May 2008. By comparison to PSP_009290_2485 (and other images acquired in 2008) we can see that the lander, heat shield, and backshell-plus-parachute are now covered by dust, so they lack the distinctive colors of the hardware or the surfaces where the pre-landing dust was disturbed.

But if the lander is structurally intact, it should cast the same shadows. While that is indeed the case for the shadow cast by the backshell (which came to rest on its side), that does not appear to be the case for the lander.

The 2008 lander images showed a very bright spot (from specular reflections) with relatively blue spots on either side corresponding to the clean circular solar panels. The shadows cast by the lander body and solar panels consists of three overlapping dark circles (see simulated image), although the specular reflection hides part of the shadows and the three shadows will merge together to a degree in actual HiRISE images.

In this observation, with illumination and viewing angles within 1 degree of those in PSP_009290_2485, we see a dark shadow that could be that of the lander body and eastern solar panel, but no shadow from the western solar panel is apparent. Because the specular reflection is no longer present on the dusty lander, the 2010 image should provide a better view of the of the west-array shadow, but it is absent.

The solar arrays were not designed to withstand significant loads such as that from perhaps 30 centimeters (1 foot) of carbon dioxide frost, so our interpretation is that this panel has collapsed. It is currently not know how much of the seasonal frost forms as falling dry-ice snow, in contrast to direct condensation of a surface ice which on Earth would be known as a hoar frost. Thus it is known how fluffy or dense this frost might be.

The comparison of these images also reveals why it has proven so difficult to locate the failed 1999 Mars Polar Lander (MPL). HiRISE searched for MPL after several southern winters had passed, so the hardware likely appears similar to the Phoenix hardware in 2010. The bright parachute is completely hidden by dust and the bright specular reflections are gone. The lander appears as an unusually large shadow from what might appear to be a boulder that is undersized relative to the shadow. The backshell has an unusual shape for a boulder, because it came to rest on its side. There is still a dark spot where the heat shield came to rest, but the bounce mark to the west is not apparent. In other words, in 2010 there are only very subtle hints of the Phoenix landing event in HiRISE images.

If that's all we had to go by, if Phoenix had failed and we were searching for it over a large landing ellipse after a polar winter had come and gone, it would be extremely difficult to deduce that this was the landing site or to understand if the landing itself had succeeded.