[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Martian Moon Phobos Hip-Deep In Powder

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www. jpl.nasa.gov

Contact: Diane Ainsworth

FOR IMMEDIATE RELEASE                        September 11, 1998

MARTIAN MOON PHOBOS HIP-DEEP IN POWDER

     New temperature data and close-up images of the Martian 
moon Phobos gathered by NASA's Mars Global Surveyor indicate the 
surface of this small body has been pounded into powder by eons 
of meteoroid impacts, some of which started landslides that left 
dark trails marking the steep slopes of giant craters.

     New temperature measurements show the surface must be 
composed largely of finely ground powder at least one meter 
(three feet) thick, according to scientists studying infrared 
data from the thermal emission spectrometer instrument on the 
spacecraft.  Measurements of the day and night sides of Phobos 
show such extreme temperature variations that the sunlit side of 
the moon rivals a pleasant winter day in Chicago, while only a 
few kilometers away, on the dark side of the moon, the climate 
is more harsh than a night in Antarctica.  High temperatures for 
Phobos were measured at -4 degrees Celsius (25 degrees 
Fahrenheit) and lows at  -112 Celsius (-170 degrees Fahrenheit). 

     The extremely fast heat loss from day to night as Phobos 
turns in its seven-hour rotation can be explained if hip-deep 
dust covers its surface, said Dr. Philip Christensen of Arizona 
State University, Tempe, principal investigator for the 
experiment on the Mars Global Surveyor spacecraft.

     "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."

     New images from the spacecraft's Mars orbiter camera show 
many never-before seen features on Phobos, and are among the 
highest resolution ever obtained of the Martian satellites.  A 
10-kilometer-diameter (six-mile) crater called Stickney, which 
is almost half the size of Phobos itself, shows light and dark 
streaks trailing down the slopes of the bowl, illustrating that 
even with a gravity field only about 1/1000th that of the 
Earth's, debris still tumbles downhill.  Large boulders appear 
to be partly buried in the surface material.

     Infrared measurements of Phobos were made on August 7, 19 
and 31 from distances ranging between 1,045-1,435 kilometers 
(648-890 miles), far enough away to capture global views of the 
Martian moon in a single spectrum. The instrument has been able 
to obtain the first global-scale infrared spectra of Earth and 
Mars in addition to the new Phobos data, bringing new insights 
about the composition of these three very different worlds.

     "Of the three, Earth has the most complex infrared spectra, 
primarily due to the presence of carbon dioxide, ozone and water 
vapor in its atmosphere," Christensen said.  "Mars, which is 
much colder than Earth because of its distance from the Sun, is 
less complex and shows only significant amounts of carbon 
dioxide. The spectrum of Phobos, however, has little structure 
because it has no atmosphere and the energy it emits is coming 
entirely from its surface."

     The new Phobos images and thermal spectrometer measurements 
are available on the Internet at: http://www.jpl.nasa.gov, 
http://mars.jpl.nasa.gov, http://photojournal.jpl.nasa.gov/, 
http://www.msss.com/ and at http://emma.la.asu.edu .

     On Monday, September 14, Mars Global Surveyor begins its 
second phase of aerobraking, using the friction from repeated 
passes through Mars' atmosphere to lower and circularize the 
spacecraft's orbit. Over the next four-and-a-half months, the 
spacecraft's flight path will be lowered from the current 11.6-
hour elliptical orbit to a two-hour, nearly circular orbit over 
the Martian polar caps. The magnetometer and thermal 
spectrometer will be turned on through December to gather data 
each time the spacecraft passes closest to Mars' surface.  In 
addition, the radio science team will be conducting gravity 
field experiments by measuring small shifts in the spacecraft's 
velocity as it passes behind the planet or is blocked from view 
by the Sun.

     The spacecraft team at JPL and Lockheed Martin 
Astronautics, Denver, is continuing to study possible options 
for deployment of the spacecraft's high-gain antenna once it has 
reached its low-altitude mapping orbit next spring.

     Mars Global Surveyor is part of a sustained program of Mars 
exploration, managed by the Jet Propulsion Laboratory for NASA's 
Office of Space Science, Washington, DC. Lockheed Martin 
Astronautics, Denver, CO, which built and operates the 
spacecraft, is JPL's industrial partner in the mission. JPL is a 
division of the California Institute of Technology, Pasadena, 
CA.

                               #####

----------
Archives located at:
http://www.meteoritecentral.com/list_best.html

For help, FAQ's and sub. info. visit:
http://www.meteoritecentral.com/mailing_list.html
----------