[meteorite-list] Mars Express: Phobos Flyby Success

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 5 Mar 2010 13:34:36 -0800 (PST)
Message-ID: <201003052134.o25LYaLP007600_at_zagami.jpl.nasa.gov>

http://www.esa.int/SPECIALS/Mars_Express/SEMIPX6K56G_0.html

Phobos Flyby Success
European Space Agency
4 March 2010

Mars Express encountered Phobos last night, smoothly skimming past at
just 67 km, the closest any manmade object has ever approached Mars'
enigmatic moon. The data collected could help unlock the origin of not
just Phobos but other "second generation" moons.
 
Something is not right about Phobos. It looks like a solid object but
previous flybys have shown that it is not dense enough to be solid all
the way through. Instead, it must be 25-35% porous. This has led
planetary scientists to believe that it is little more than a "rubble
pile" circling Mars. Such a rubble pile would be composed of blocks both
large and small resting together, with possibly large spaces between
them where they do not fit easily together.

Last night's flyby was close enough to give scientists their most
exquisite data yet about the gravitational field of Phobos. Mars Express
locked onto the radio signal from Earth at around 21:20 CET (20:20 UT).
The radio frequency oscillators on the ground are 100 000 times more
stable than those on the spacecraft, so for this experiment, which
required the best precision possible, the signal was sent up to Mars
Express and then returned by the spacecraft to the ground.
 
The radio waves travel at the speed of light and took 6 minutes 34
seconds to travel from Earth to the spacecraft last night. So the round
trip time was 13 minutes 8 seconds. Once the signal was received back at
Earth, it was clearly strong and good. So strong that radio amateurs
were also able to lock onto the signal, although their equipment would
not be able to detect the subtle variations induced by the gravity of
Phobos.

Now that the data are all collected, the analysis can begin.First will
be an estimate of the density variation across the moon. This will tell
scientists just how much of Phobos' interior is likely to be composed of
voids.

"Phobos is probably a second-generation Solar System object," says
Martin P??tzold, Universitat Koln, Cologne, Germany, and Principal
Investigator of the Mars Radio Science (MaRS) experiment. Second
generation means that it coalesced in orbit after Mars formed, rather
than forming concurrently out of the same birth cloud as the Red Planet.
There are other moons around other planets where this is thought to have
been the case too, such as Amalthea around Jupiter.
 
Whatever the precise origin, Phobos will eventually crumble back into
this disrupted state. It is gradually spiralling towards Mars and will
eventually be pulled apart. "It came from debris, it will return to
debris," says P??tzold. In the meantime, it is there to be studied and
explored.

Last night's flyby was just one of a campaign of 12 Mars Express flybys
taking place in February and March 2010. For the previous two, the radar
was working, attempting to probe beneath the surface of the moon,
looking for reflections from structures inside. In the coming flybys,
the Mars Express camera will take over, providing high resolution
pictures of the moon's surface.
 
More information
 
Updates as the flybys continue will be posted on the Mars Express blog
<http://webservices.esa.int/blog/blog/7>.
 
 
Contacts for editors:
 
Martin Patzold
Principal Investigator of the Mars Radio Science (MaRS) experiment
Universitat Koln, Germany
Email: mpaetzol at uni-koeln.de

Olivier Witasse
ESA Project Scientist Mars Express
ESTEC, The Netherlands
Email: owitasse at rssd.esa.int
 
Received on Fri 05 Mar 2010 04:34:36 PM PST