[meteorite-list] Mars Express Image: Martian Moon Phobos in Detail

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Nov 11 13:24:35 2004
Message-ID: <200411111824.KAA18565_at_zagami.jpl.nasa.gov>


Martian moon Phobos in detail
European Space Agency
Mars Express
11 November 2004

These images, taken by the High Resolution Stereo Camera (HRSC) on board
ESA's Mars Express spacecraft, are Europe's highest-resolution pictures
so far of the Martian moon Phobos.
These HRSC images show new detail that will keep planetary scientists
busy for years, working to unravel the mysteries of this moon. The
images show the Mars-facing side of the moon, taken from a distance of
less than 200 kilometres with a resolution of about seven metres per
pixel during orbit 756.

Images of Phobos as shown here had already been taken at lower
resolution in previous orbits (413, 649, 682, 715 and 748). In the
coming months, these first pictures will be followed by a series of
images taken in subsequent fly-bys.


Collection of Phobos images from different orbit passes

The Mars Express spacecraft periodically passes near Phobos about one
hour before it flies at an altitude of only 270 kilometres above the
Martian surface, just above the atmosphere. Within minutes, the orbiting
spacecraft turns from its attitude where it points at Mars to train its
camera on this little world.

The HRSC provided an unprecedented near-simultaneous group of 10
different images of the surface, enabling the moon's shape, topography,
colour, "regolith" light-scattering properties, and rotational and
orbital states to be determined. The regolith is the small-grained
material covering most non-icy planetary bodies, resulting from multiple
impacts on the body's surface.

Phobos in 3D
These images have surpassed all previous images from other missions in
continuous coverage of the illuminated surface, not blurred and at the
highest resolution. The US Viking Orbiter obtained a few small areas
sampled at an even higher resolution of a few metres per pixel, but
these were not so sharp due to the close and fast fly-by.

The global "groove" network is seen in sufficient detail to cover the
Mars-facing surface continuously from near the equator up to the north
pole with regular spacing between the grooves. It now may be possible to
determine whether the grooves existed before the large cratering events,
and exist deep within Phobos, or came after the cratering events and
were superimposed on them.

Much more detail is seen inside the various-sized craters, showing some
with marked albedo variations. Some craters have dark materials near the
crater floors, some have regolith that slid down the crater walls, and
some have very dark ejecta, possibly some of the darkest material in our
Solar System.

Phobos in black and white, close-up

This tiny moon is thought to be in a "death spiral", slowly orbiting
toward the surface of Mars. Here, Phobos was found to be about five
kilometres ahead of its predicted orbital position. This could be an
indication of an increased orbital speed associated with its secular
acceleration, causing the moon to spiral in toward Mars.

Eventually Phobos could be torn apart by Martian gravity and become a
short-lived ring around Mars, or even impact on the surface. This orbit
will be studied in more detail over the lifetime of the Mars Express.

The 3D anaglyph image was generated from a combination of the nadir and
the blue channel. The colour image was calculated from the three colour
channels and the nadir channel. Due to geometric reasons the scale bar
is only valid for the centre of the image.
Received on Thu 11 Nov 2004 01:24:29 PM PST

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