Spacecraft Transmits Clues to Martian Moon’s Surface

The surface of the Martian moon Phobos is probably covered with a meter-thick layer of finely ground powder, the Jet Propulsion Laboratory reported today.

JPL scientists made their determination based on infrared photos transmitted to Earth by the Mars Global Surveyor, a spacecraft circling the Red Planet and its moons on a mapping mission.

Scientists drew their conclusion based on the large variations in Phobos’ surface temperature, which was as high as 25 degrees Fahrenheit in some sunlit areas, and as low as minus 170 degrees in unlit areas only kilometers away.

The fast rate of heat loss as the surface of Phobos goes from day to night in its seven-hour rotation can be explained if a hip-deep layer of dust covers the moon’s surface, said Philip Christensen, principal investigator for the experiment on the spacecraft.

Scientists hypothesized that the powdery surface may have been created by meteor impacts over the eons.

“The infrared data tells us that Phobos, which does not have an atmosphere to hold heat in during the night, probably has a surface composed of very small particles that lose their heat rapidly once the sun has set,” Christensen said.

“This has to be an incredibly fine powder formed from impacts over millions of years, and it looks like the whole surface is made up of fine dust,” he said.

The infrared photos were taken on Aug. 7, 19 and 31 from distances ranging from 648 to 890 miles away.

The pictures can be viewed on the Internet at www.jap.nasa.govorphotojournal.jpl.nasa.gov.