[meteorite-list] Mars Express Acquires Sharpest Images of Martian Moon Phobos

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 31 Jul 2008 16:06:44 -0700 (PDT)
Message-ID: <200807312306.QAA09064_at_zagami.jpl.nasa.gov>

http://www.esa.int/esaCP/SEM5H48N9JF_index_0.html
 
Mars Express acquires sharpest images of martian moon Phobos
European Space Agency
30 July 2008

Mars Express closed in on the intriguing martian moon Phobos at 6:49 CEST
[0449 UTC] on 23 July, flying past at 3 km/s, only 93 km from the moon. The
ESA spacecraft's fly-bys of the moon have returned its most detailed
full-disc images ever, also in 3-D, using the High Resolution Stereo Camera
on board.
 
Phobos is what scientists call a 'small irregular body'. Measuring 27 km x
22 km x 19 km, it is one of the least reflective objects in the Solar
System, thought to be a capture-asteroid or a remnant of the material that
formed the planets.

The best images of Phobos ever
 
The HRSC images, which are still under processing, form a bounty for
scientists studying Phobos. They are a result of observations carried out
over several close fly-bys of the martian moon, performed over the past
three weeks. At their best, the pictures have a resolution of 3.7 m/pixel
and are taken in five channels (in the stereo channel) for images in 3-D and
(in the photometric channels) to perform analyses of the physical properties
of the surface.

The images obtained by several other spacecraft so far have either been of a
lower resolution, or not available in 3D and have not covered the entire
disc of Phobos. This is also the first time that portions of the far-side of
the moon have been imaged in such high resolution (Phobos always faces Mars
on the same side).

Scientific bounty
 
In observing Phobos, Mars Express benefits from its highly elliptical orbit
which takes it from a closest distance of 270 km from the planet to a
maximum of 10 000 km (from the centre of Mars), crossing the 9000 km orbit
of the martian moon. Mars Express imaged the far-side of Phobos (with
respect to Mars) for the first time after NASA's Viking mission, by flying
outside the spacecraft's orbit around Mars.

Phobos-Grunt (Phobos soil), a Russian sample-return mission, is due to for
launch in 2009. It is expected to land on the far-side of Phobos at a region
between 5 deg south to 5 deg north, and 230 deg west to 235 deg west. This
region was last imaged in the 1970s by the Viking orbiters.

The HRSC observations have been awaited eagerly to better assess and
characterise the choice of the landing site.

The moon's remarkably grooved surface can be seen in the pictures quite
clearly. The origin of these grooves is still debated. It is not known
whether they are produced by ejecta thrown up from impacts on Mars, or if
they result from the surface regolith, or soil, slipping into internal
fissures.

In this image, at least two families of grooves with distinct orientations
can be seen along with an elongated crater.

The stereo observations (resolution 3.7 m/pixel) are important for
structural analysis and they will be used to derive a digital terrain model
(a 3-D map of the surface that includes elevation data). The extra
photometric channels (at 7.4 m/pixel) make it possible to study the
properties of the Phobos regolith at micron to millimetre scales.

An operational challenge
 
Managing the close fly-bys was an operational challenge, made possible by
spacecraft operations engineers and scientists who worked together to
specially optimise Mars Express's trajectory and obtain the best possible
views.

The observation made use of a spacecraft slew, a special manoeuvre whereby
the body of the spacecraft is rotated against the direction of motion, to
effectively lower the speed at which the target passes in the field of view
of the camera. This makes it possible to avoid blurring of the pictures
despite the high fly-by velocities, whilst maintaining acceptable exposure
time.

The HRSC Super Resolution Channel (SRC) also observed during this close
fly-by, with a nominal resolution of 90 cm/pixel. As expected, despite the
slew, some residual motion blur has crept into the image, but much detail is
expected to be recovered after further processing.

In the days running up to the observation, the primary star-tracker - a
navigation device that helps the spacecraft point its instruments at the
target accurately - experienced some temporary difficulty in recognising the
star constellations in its field of view, leaving the spacecraft operating
on its secondary system. Concerned that this might affect this critical
observation, the team at ESA's European Space Operations Centre (ESOC) in
Darmstadt, Germany, worked intensely to recover the primary system and were
able to switch back successfully two days before the fly-by.

Notes for editors:
 
The Principal Investigator (PI) for the HRSC experiment on ESA's Mars
Express is Prof. Dr Gerhard Neukum, who also designed the camera
technically. The HRSC science team consists of 45 Co-Investigators from 32
institutions located in 10 nations. The camera was developed at the German
Aerospace Center (DLR) under the PI in cooperation with industrial partners
(EADS Astrium, Lewicki Microelectronic GmbH and Jena-Optronik GmbH). It is
operated through ESA/ESOC by the DLR Institute of Planetary Research, where
systematic processing of the image data is carried out. The scenes shown
here were processed by the PI group at the Institute for Geosciences of the
Freie Universitaet Berlin in cooperation with the DLR Institute of Planetary
Research, Berlin.

[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaCP/SEM5H48N9JF_index_1.html ]
Received on Thu 31 Jul 2008 07:06:44 PM PDT