mars as never seen before
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Mars
2.21April 2004 Vol 45
Mars as neverseen before
Images from the High Resolution
Stereo Camera on Mars Express
reveal the surface of the Red Planet
in unprecedented detail – and should
have the whole planet mapped at
high resolution in just two years.
Over the next six pages, Ernst
Hauber and Gerhard Neukum set
the scene and reveal some of the
spectacular images already captured.
(All images are courtesy of ESA/
DLR/FU Berlin/G Neukum unless
otherwise credited.)
1: The HRSC camera (DLR/FU Berlin).
2 (main): The HRSC is a multipleline-scanner with nine CCD linesensors and the additionalSuper Resolution Channel (DLR).
On 25 December 2003 the first European
planetary spacecraft mission ever, Mars
Express, was successfully inserted into
orbit around Mars. A few days before, its lan-
der module Beagle 2 had been separated.
Unfortunately, Beagle 2 has failed to communi-
cate since its first radio contact was missed
shortly after it was due to land on Mars on
Christmas Day. The Beagle 2 Management
Board met in London on 6 February and, follow-
ing an assessment of the situation, declared the
lander lost. The orbiter module Mars Express is
more fortunate, however. The spacecraft reached
its near-polar mapping orbit on 28 January
2004, after several manoeuvres to reduce the
eccentricity of the orbit, which was initially very
high. Meanwhile, the instruments performed
their first checks and began to acquire scientific
data. All its instruments are working well. The
40 m antenna of the ground-penetrating radar
MARSIS (Mars Advanced Radar for Subsurface
and Ionospheric Sounding) will be deployed
no earlier than April. This activity and the
subsequent test of this last instrument will mark
the end of the commissioning phase, during
which the science observations are restricted
by constraints from the spacecraft side.
Even within this commissioning phase, sig-
nificant scientific results have been reported.
For example, the French-built visible and
infrared spectrometer Omega (Observatoire
pour la Mineralogie, l’Eau, la Glace et
l’Activite) is the first instrument in history to see
firm and direct evidence for water molecules on
the martian surface. These findings were sup-
ported by data from the other two spectrom-
eters, the Italian PFS (Planetary Fourier
Spectrometer), a new high-resolution spec-
trometer of unprecedented accuracy, and the
French SPICAM (SPectroscopy for the
Investigation of the Characteristics of the
Atmosphere of Mars), a lightweight UV–IR
instrument on board the Mars Express orbiter
dedicated to the study of the martian atmo-
sphere and ionosphere. Both instruments
observed signatures from water in their spectra.
Mars
2.22 April 2004 Vol 45
Mars Express is Europe’s first planetary
explorer, a collaboration among 10
countries that carries instruments to
examine the surface, atmosphere and
space environment of Mars. Among the
instruments is the High Resolution Stereo
Camera, which has already produced
spectacular images of scientific value.
Here we present a selection of these first
images, together with a summary of the
capabilities and aims of this instrument.
The images so far show details of surfaces
shaped by volcanic, tectonic and fluid
flow processes during the history of the
planet. HRSC has a list of targets for
observation that should throw light on
some problematic aspects of martian
evolution, such as the existence of bodies
of surface water, and the influence of
tectonic and volcanic processes.
Abstract
3: The HRSC images acquired from January through early March 2004(orbits 1–160), are superposed on a background topographic map of Mars(derived from Mars Orbiter Laser Altimeter data; simple cylindricalprojection). (DLR/FU Berlin.)
The first PFS data also show that the carbon
oxide distribution is different in the northern
and southern hemispheres of Mars. ASPERA
(Analyzer of Space Plasma and Energetic
Atoms), a plasma and energetic neutral atoms
analyser built in Sweden, is aiming at answer-
ing the fundamental question of whether solar-
wind erosion led to the present lack of water on
Mars. Preliminary results show a difference in
the characteristics between the area of impact
of the solar wind and measurements made in
the tail of Mars’ magnetosphere.
On 9 January 2004 the German High
Resolution Stereo Camera (HRSC) began to
acquire multispectral stereo images of the mar-
tian surface with a lateral resolution of between
10 and 20 m/pixel. Imaging and mapping the
martian surface by the HRSC is one of the main
goals of Mars Express. The camera is a mult-
iple line-scanner and works in the pushbroom
mode. Nine CCD line sensors, each with 5184
pixels, are operated in parallel (figure 1). Five
panchromatic lines provide high-resolution
images for stereo and photometric analyses. The
stereo information is derived from the pan-
chromatic sensors, which observe the surface
with different imaging geometries as the space-
craft moves along the orbit. Four lines are
equipped with colour filters for multispectral
investigations. An additional Super Resolution
Channel (SRC) is equipped with a CCD frame
sensor and provides very high-resolution images
(from 2–3 m/pixel) that are embedded within
the HRSC context (figure 2). Such imagery is
ideal to study the variety of known (and possi-
bly unknown) surface processes that have acted
on Mars (see “What will HSRC do?” below).
In particular, the combination of broad areal
coverage with high lateral resolution is an
important step forward from previous imaging
experiments from Mars orbit. Due to the
improvement in lateral resolution of HRSC
(10–100 m) as compared to the Mars Orbiter
Laser Altimeter (MOLA; 100–1000 m), it is
also an ideal tool to investigate the topography
of small-scale surface features. While the
number of colour channels is restricted to four
(blue, green, red and near infrared), their high
lateral resolution complements the capacities of
spectrometers such as the Thermal Emission
Imaging System (Themis) on Mars Odyssey or
Omega on Mars Express, which have high spec-
tral, but limited lateral resolution.
What will HSRC do?
The scientific objectives and measurement goals
of the HRSC experiment on Mars Express have
been formulated by the international team of 45
co-investigators from 10 countries under the
leadership of one of the authors (Neukum), who
is the Principal Investigator of the instrument.
The major scientific objective of the HRSC is the
study of the evolution of the martian surface
structure and morphology through time and the
geological processes involved. Another impor-
tant topic is the investigation of atmospheric
characteristics and dynamic atmospheric phe-
nomena. When imaging conditions are
favourable, we will also take images of the two
Mars
2.23April 2004 Vol 45
5: Erosion shaped the chaoticterrains east of the giant troughs of VallesMarineris near the martian equator. Millions ofcubic kilometres of rock have been removed by theaction of water. The elevation difference in this image is about3000 m. The detail shown in this perspective view is 60 km across.The image was taken during orbit 18 on 14 January 2004 (centred at 5.5°Sand 37°W, resolution 11 m/pixel, altitude 270 km, north is towards the upper right).
4: A perspective view of a mesa in the chaotic terrains in the true colours of Mars. The summit plateaustands about 3 km above the surrounding terrain. The original surface was dissected by erosion, onlyisolated mesas remained intact. The large crater in the upper left background has a diameter of7.6 km. This picture was taken in orbit 18 on 14 January 2004 (centred at 9°N and 37°W, resolution12 m/pixel, altitude ~270 km, north is at the top).
small martian moons, Phobos and Deimos. In
particular, HRSC images will help to reveal the
past climate and the role of water throughout
martian history, the evolution of volcanism and
tectonism on Mars, and the interactions between
the atmosphere and the surface. An additional
objective is to determine the characteristics of
past, present, and future landing sites.
In order to meet these scientific objectives, the
following imaging capabilities have been imple-
mented in the HRSC experiment:
� Characterization of surface features and mor-
phology at high spatial resolution (~10 m/pixel)
� Characterization of surface topography at
high spatial and vertical resolution with dedi-
cated stereo imaging
� Characterization of surface features and mor-
phology at “super-resolution” (~2 m/pixel)
� Terrain classification at high spatial resolu-
tion by multispectral image data
� Scattering properties of the regolith and the
atmosphere by multiphase angle observations
� Characterization of atmospheric properties
and phenomena by limb sounding and nadir
observations
� Imaging quasi-simultaneously at high-resolu-
tion with stereo, in colours and at different
phase angles in order to avoid differences in
atmospheric and illumination conditions that
up to now have caused severe problems in the
photogrammetric data evaluation
� Acquisition of nested-in images at super-
resolution for exact georeferencing.
Orbital imagery in the 10 m/pixel range and
in the 2 m/pixel range as obtained by the HRSC
experiment is an essential prerequisite for
detailed surface exploration and for the solution
of open questions such as the role of water
throughout martian history, or volcanic evolu-
tion. The ability to study morphologic surface
features in more detail by photogeological
analysis is complemented by the possibility of
deriving ages even for small features such as
valley floors or surfaces of former lakes. The
HRSC high-resolution imagery also makes it
possible to count craters much smaller than the
features themselves – such data will be essential
for the reconstruction of the geological history.
The stereo and colour capabilities of the HRSC
significantly enhance the interpretation of the
imaging data. For instance, the accurate deter-
mination of erosion rates and modelling of var-
ious geologic processes such as water flow and
emplacement of lava flows, is presently limited
by the lack of information on local elevation dif-
ferences. The colour information will be impor-
tant for terrain classification, for the detection
of compositional layering and variations in the
composition of surface materials, and for the
recognition of different surface processes. The
multiphase imagery, finally, will allow the study
of physical properties of the martian soil and
will support the photogrammetric data evalua-
tion by providing a second stereo angle triplet
(in combination with the nadir channel).
If Mars Express fulfills its mission goals over
the entire planned lifetime of one Mars year
(two Earth years), HRSC will achieve one of the
largest extraterrestrial mapping efforts yet:
Mars
2.24 April 2004 Vol 45
6: Reull Vallis is a channel once formed by flowing water. The dark materialis probably either wind-blown material or sediments deposited by water.The image was taken in orbit 22 on 15 January 2004 (the location is east ofthe Hellas basin at 41°S and 101°E, image area is 100 km across,resolution 24 m/pixel, from a height of 540 km, north is at the top).
7: Kasei Vallis is the largest outflow channel on Mars. It wasformed by erosion involving liquid water or glaciers. Thisperspective view in false colours shows the depression ofEchus Chasma, the head of Kasei Vallis. The floor is coveredby lava flows (in the false-colour image showing up as bluishmaterial), obscuring any previous traces of water. The imagewas taken on orbit 71 on 1 February 2004 (centred at 0°Nand 79.5°W, resolution 12 m/pixel, altitude about 270 km,image is about 50 km across, south is at the top).
50% of the surface will be mapped at resolu-
tions better than 20 m/pixel, 70% at better than
40 m/pixel, and the entire surface at better than
100 m/pixel. If the mission lasts four years we
will be able to cover nearly 100% of the surface
of Mars at a resolution better than 20 m/pixel.
For comparison, the surface of Mars is equal to
the total land surface of all continents on Earth.
Scientific targets
The HRSC team has compiled a list of more than
1500 geoscientific targets by mapping the sites
and regions over the whole of Mars that hold the
greatest scientific interest. This huge list contains
all information with respect to geographic loca-
tion, extent, preferred imaging mode and reso-
lution, preferred season and illumination
conditions, as well as information on already
existing image coverage, classification of geo-
logic processes involved in the formation of each
target area and others. The list also covers the
field of surface/atmosphere interactions and of
variable features. Targets of specific interest for
cartographic and photogrammetric research
include the crater Airy, which defines the 0° lon-
gitude, and landing sites in order to refine the
geodetic control network. These targets require
more than one observation during the mission.
We also compiled a list of atmospheric targets for
limb sounding observations, which are particu-
larly interesting for atmospheric science. At least
two to three limb measurements for each Earth
month are envisaged throughout the mission.
Due to favourable conditions such as high
telemetry rates, large areas could be imaged in
the early stages of the mission. Some of the first
images cover areas as much as 60 to 200 km
wide and up to 4000 km long (figure 3). The
total area covered in the first month of imaging
is about 4 million km2, about half the area of
Europe. Several major physiographic provinces
have been sampled already, including the south
polar cap, Hellas, Tharsis with several shield
volcanoes, the Valles Marineris, the chaotic
regions (figures 4 and 5, and on the cover of this
issue), the outflow channels Reull and Kasei
Valles (figures 6 and 7), and different parts of
the southern highlands. We also took long
image traverses across some of the most promi-
nent volcanoes on Mars. Spectacular images of
the calderas of Olympus and Ascraeus Montes
in Tharsis (figures 8 and 9), and of Albor and
Hecates Tholi (figure 10) in Elysium, allow for
detailed investigations of the topography and
morphology of their floors. Tectonic surface
features and the aureole of Olympus Mons were
also shown in great detail (figures 11 and 12).
While the total data volume transmitted so far
is high, other constraints prevented us achieving
some of our initial imaging objectives. A hard-
ware problem meant that the power perfor-
mance of the spacecraft’s solar panels was lower
than expected. As a consequence, the spacecraft
could make fewer pointing manoeuvres and the
flexibility of operations was reduced. Therefore
we have acquired only two adjacent image strips
so far, which make up our only image mosaic
existing at the time of writing (March 2004).
The high dust content of the atmosphere in
Mars
2.25April 2004 Vol 45
8: Olympus Mons is the largest shield volcano in the solar system. Its caldera has a diameter of60 × 90 km. The image was taken during orbit 37 on 21 January 2004 (centred at 18.3°N and133°W, resolution 18 m/pixel, image is about 102 km across, altitude ~400 km, south is at the top).
9: The summitcaldera of AscraeusMons has experiencedseveral stages of collapse.The diameter of the calderacomplex is between 50 km and60 km. It is up to 4000 m deep. Theimage was taken on orbit 68 on 31January 2004 (centred at 11.3°N and104.4°W, resolution 16 m/pixel, altitudeabout 360 km, north is towards the upper right).
early 2004, also noted by the two Mars
Exploration Rovers and other orbiting instru-
ments, meant that images of some regions with
low elevations have low contrast. For example,
the supposed landing site of Beagle 2 in Isidis
Planitia was imaged by HRSC in search of clues
to the descent (such as the parachute). The
dusty atmosphere, however, made any success-
ful search in the images impossible.
The dust also caused another problem early in
the mission. It is not easy presently to arrive at
the true colours of the martian landscape in the
reproduction of images because Mars is very
dusty and the scenes were taken when the Sun
was high. Under these atmospheric conditions
the dust in the atmosphere acts as tiny red fil-
ters and one looks at the surface as if in a dif-
fuse reddish glow with a somewhat fuzzy
appearance. Imagine that you had to judge the
colour of a cloth in a room with artificial red-
dish light – it would be very difficult. The
colours in most pictures released so far are close
to true colours, but a slight tint in the reddish
or bluish direction from non-perfect adjust-
ments of the colour histograms cannot be
excluded due to the somewhat abnormal “see-
ing” conditions.
While the focus of HRSC observations is on
surface observations of Mars, additional objec-
tives are the investigation of the planet’s atmo-
sphere. On two occasions, on 16 January and
1 February 2004, Mars Express together with
the NASA rover Spirit in Gusev crater made the
first joint observations of surface and atmo-
sphere. HRSC and other instruments on Mars
Express observed the rover’s landing site from
orbit, while simultaneously some of the rover
instruments looked upwards into the sky.
Looking to the future
The HRSC on Mars Express will be able to
close the existing gap between medium to low-
resolution coverage on the one hand and the
very high-resolution images of Mars Global
Surveyor as well as the in-situ observations and
measurements by landers on the other hand.
The HRSC on Mars Express will make a major
contribution to the areas of geosciences, atmo-
spheric sciences, photogrammetry/cartography,
and spectrophotometry of Mars. Special
emphasis will be put on the evolution of the
martian surface due to volcanic processes and
the role of water throughout martian history.
The instrument will obtain images containing
morphologic and topographic information at
high spatial and vertical resolution of unique
photogrammetric quality allowing the improve-
ment of the martian cartographic database
down to scales of 1:50 000.
The HRSC team will present its first major
scientific discoveries at the Lunar and Planetary
Science Conference, Houston, and at the 1st
General Assembly of the European Geosciences
Union, Nice, France, in late April 2004. �
Ernst Hauber, Inst. of Planetary Research, GermanAerospace Centre (DLR), Berlin, Germany;Gerhard Neukum, Inst. of Geosciences, FreieUniversität Berlin, Berlin, Germany.
Mars
2.26 April 2004 Vol 45
10: The summit caldera of Hecates Tholus,the northernmost volcano of the Elysiumvolcano group. The volcano reveals multiplecaldera collapses. On the flanks of HecatesTholus, several flow features related towater (lines radiating outwards) and pitchains related to lava can be observed. Thevolcano has an elevation of 5300 m, thecaldera has a diameter of maximum 10 kmand a depth of 600 m. The image was takenon orbit 32 on 19 January 2004 (centred at150°E and 31.7°N, resolution 25 m/pixel,altitude about 560 km, north is at the top).
11: The AcheronFossae are a large
system of tectonic featuresnorth of Olympus Mons, near the
Tharsis region. They were probably formedby large-scale lithospheric extension. The
largest grabens are more than 2 km deep. The imagewas taken from a height of 675 km during orbit 37 on 21
January 2004 (centred at 37°N and 132°W, resolution 30 m/pixel,the image width is about 150 km, north is towards the upper right).
12 (right): The eastern flankof the giant shield volcano
Alba Patera is dissected bynumerous tectonic grabens.
They reflect the complexevolution of Alba Patera andthe entire Tharsis region of
Mars. The image was takenon orbit 68 on 31 January2004 (centred at at 40°N
and 103°W, resolution32 m/pixel, altitude about
720 km, image width about112 km, north is at the top).
Mars
2.27April 2004 Vol 45
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