A Selection of Mars Express Scientific Results (French contribution)
The Source Crater of Martian Shergottite Meteorites
From source to sink: Meteorites from Mars have been known since the 1970s but Stephanie Werner at the University of Oslo (CEED) and her team have been able to identify the source crater for shergottites, the largest group of Martian meteorites. The source region on Mars was probably impacted about 3 million years ago by a medium-size body and they ended their space journey at the Earth's surface a few thousand years ago.
The geological evolution of other planets is difficult to study because their sufaces cannot be accessed other than by space missions. But because meteorites derived from some planetary bodies have landed on Earth we can analyze these alien rocks in the laboratory. We can determine the age and the mineralogy and therefore derive information on the geology and evolution of the parent body, and detailed laboratory analyses also tell us about a planet's magmatic and petrologic evolution. However, we do not know the geographic location and geological setting, and it is therefore crucial to find out from which site the meteorite was ejected to Earth.
The only method to establish a time-constrained geological evolution on terrestrial planets is to determine the crater density on their surfaces. The higher the density is, the older the surface is. Calibrating these crater densities within an absolute time frame requires several steps, starting with a model for the moon where crater frequency can be related to absolute ages derived from lunar samples.
Stephanie Werner and her collaborators have for the first time been able to identify the source crater, Mojave (7.5°N, 33.0°W), for the largest group of Martian meteorites, the so-called shergottites. Now that they have identified the crater's location and geological setting for these meteorites we can place the mineralogy and ages of the meteorites in a geological context. A long-lasting debate about the original age for the meteorites, younger than 600 million years old or older than 4.1 billion years old has now been settled in favour of the old ages.
Mojave crater formed a few million years ago and is identified as the region source of the most common Martian meteorites (shergottites). The coloured areas reveal the presence of mafic minerals (both pyroxene and olivine) as seen by OMEGA/MEx and CRISM/MRO. The same minerals are also found in the Martian meteorites from terrestrial laboratory measurements.
The Source Crater of Martian Shergottite Meteorites by Stephanie C. Werner, Anouck Ody and François Poulet - Science Express, on March 6th 2014 / Science, on March 14th 2014, doi:10.1126/science.1247282.
A complex magmatic history for Mars
Mars is a volcanic world, covered nearly entirely in basaltic rocks. While the planet's geological history remains elusive for lack of in-situ samples or probes of its internal structure, its uniform surface composition was thought to result from an unremarkable magmatic history. Recently, one study led by ESO and the IAS has revealed a new rock type on Mars, akin to anorthosite (made of plagioclase feldspar (90-100%), and a minimal mafic component (0-10%). Previously only known to be associated with the lunar highlands and with peculiar magmatic formations on Earth, the presence of anorthosite on Mars demonstrates that the planet experienced a more complex magmatic history than previously thought, and provides unique opportunities to investigate early crustal formation mechanisms on a planetary body other than Earth.
These discoveries where made possible thanks to the NASA Mars Reconnaissance Orbiter and ESA Mars Express missions, including the CRISM and OMEGA infrared spectrometers, and with the support of CNES.
Example of anorthosite rock (in green) detected by the CRISM/MRO instrument (NASA) on an old hillock (in the south) and on an eroded crater wall (in the north) of a mountainous region of Mars. The topography was reconstructed using Mars Express (ESA) HRSC stereo camera data.
A seasonal ozone layer over the Martian South Pole
For the past decade, ESA's Mars Express orbiter has been observing atmospheric structure on the Red Planet. Among its discoveries is the presence of three separate ozone layers, each with its own characteristics. A new comparison of spacecraft data with computer models explains how global atmospheric circulation creates a layer of ozone above the planet's winter poles.
Ozone molecules are easily destroyed by solar ultraviolet light and by chemical reactions with hydrogen radicals (HOx), which are released by photolysis (splitting) of water (H2O). Until the early 1970s, no one could be sure whether ozone existed on any of the other planets. Ozone was then detected on Mars and it has since been discovered by ESA's Venus Express mission. On Mars, the ozone concentration is typically 300 times thinner than on Earth, although it varies greatly with location and time. In recent years, the SPICAM UV spectrometer on board Mars Express has shown the presence of two distinct ozone layers at low-to-mid latitudes. These comprise a persistent, near-surface layer below an altitude of 30 km, and a separate layer, which is only present in northern spring and summer, and whose altitude varies from 30 to 60 km.
Scientists from LATMOS, France, have analyzed approximately 3,000 occultation sequences and vertical ozone profiles collected by SPICAM on the night side of Mars. They provide evidence for the existence of a third ozone layer which exists 40-60 km above one, or both, of the winter poles.
Typical configuration of Mars during summer in the Northern hemisphere (winter in the South). Oxygen atoms are released by the dissociation of carbon dioxide molecules exposed to UV radiations. The oxygen follows a path (indicated by the arrow) towards the South Pole, carried by the atmospheric circulation dominating during this season. Once arrived at the South Pole where a permanent night reigns, the oxygen atoms recombine to form the ozone layer observed by SPICAM at about 50 km.
Rocket dust storms on Mars
One of the most exotic aspects of Mars' atmosphere is the presence of microscopic grains of dust hanging in the air which play a crucial impact on the of the planet's climate. However, the question of the continuous renewal of this dust is still unanswered. A team of scientists from the IPSL used an innovative approach using a new numerical model which enables to forecast the weather at very small scale in a particular region of Mars. They studied the evolution of a violent dust storm seen by the instrument Omega of the European mission Mars Express.
If a dust storm begins at first by the uplifting of dust from the Martian soil, the scientists discovered that a column of dust with a spectacularly fast ascension can appear–a "rocket dust". Then considerable quantities of dust are injected up to 30 or 50 kilometres above the surface of Mars. The mechanism creating these rocket dust storms on Mars is called a deep convection.
These discoveries enable to propose the first solid explanation for the enigmatic enriched layers of dust observed at high altitude on Mars by Mars Reconnaissance Orbiter. The permanent renewal of the dust in Mars' atmosphere is also better understood. Rocket dusts have numerous other implications on atmospheric dynamics, water cycle and chemistry on Mars. Moreover, knowing the potential danger guarantees the success of future robotic and human missions sent to Mars.
Numerical modelling of the growth of the dust cloud detected by Mars Express. This is the temporal evolution of the quantity of dust in Mars' atmosphere. In 4 hours, the cloud climbs up to 35 km altitude. The cloud ends by horizontally unravelling in a layer subsisting at high altitude, which lowers during the night but climbs back the next day.
© LMD / Aymeric Spiga
Craters expose action of ground water beneath Martian uplands
A new study of the ancient, cratered highlands of Mars has detected numerous exposures of minerals that were altered by underground water during the planet's early history. The data indicate that subsurface water persisted for prolonged periods of time during the first billion years of the planet's existence.
At the present time, atmospheric pressure is so low on Mars that water cannot exist on its surface. However, studies made by orbiting spacecraft and surface rovers show that Mars was once much warmer and wetter than it is today.
The most obvious evidence is the presence of landforms such as dry valleys and fossil deltas, which were almost certainly created by running water. Other compelling evidence is provided by widespread, but fairly localized, detections of hydrated minerals–the result of chemical alteration of rocky material due to the presence of water.
Aqueously altered minerals–generally classified as hydrated silicates and phyllosilicates–are absent from most of the Martian surface, except in a number of outcrops of the oldest geologic units, indicating that the planet has been dry for most of its history. However, an international team of scientists reports in the journal Icarus that these tell-tale minerals have been detected in Tyrrhena Terra, a region of ancient highlands that is sandwiched between the northern plains of Isidis Planitia and the huge Hellas impact basin.
OMEGA/Mars Express and CRISM/MRO spectro-imagers discovered different hydrated minerals in the crater at the centre of the image and on most of its ejecta blanket, excavated from depth down to over 2 km during the impact. The image on the right shows pixels where OMEGA detected hydrated silicates. It is one of the biggest crater of the area on which these minerals have been identified.
Image courtesy of D. Loizeau et al. / Icarus 219 (2012) 476-497
A glow in the Martian night throws light on atmospheric circulation
A faint, infrared glow above the winter poles of Mars is giving new insights into seasonal changes in the planet's atmospheric circulation. The tell-tale night emission was first detected in 2010 in observations made by the OMEGA imaging spectrometer on ESA's Mars Express orbiter.
Infrared emissions are not unusual in planetary atmospheres. In the upper atmospheres of both Venus and Mars, carbon dioxide (CO2) and nitrogen (N2) molecules are split or photodissociated by solar ultraviolet light. This produces oxygen and nitrogen atoms in the region known as the thermosphere, at an altitude of about 80-90 km above each planet's dayside.
As the sinking gas comes into contact with carbon dioxide molecules in the atmosphere, the atoms of oxygen and nitrogen recombine. This recombination process results in an ultraviolet nightglow from nitric oxide (NO), as well as a near-infrared oxygen (O2) emission at 1.27 microns.
As predicted by general circulation models of Mars, all of the OMEGA oxygen nightglow observations were obtained at high latitudes, during the winter night. This location coincides with the region where cooler gas is sinking above the pole which is experiencing long-term darkness–similar to the winter pole on Earth.
The OMEGA instrument on Mars Express has detected oxygen emission at the night side of Mars. The emission, at a wavelength of 1.27 µm, was detected on three occasions during a series of 40 observations made by OMEGA above the planet's limb.
The panels above show, from left to right:
- a 2.2° wide swath of the observed limb at night with emission coded in pink;
- the vertical distribution of the intensity observed in megaRayleigh (MR) - integration over azimuth. The red line is a smoothed version of the distribution;
- the integrated observed spectrum, showing emission only at 1.27 µm.
Image courtesy of Bertaux, J.-L., et al. (2012)
Mars Express radar revives the question of a Martian polar ocean
By studying data accumulated over five years by the MARSIS radar on board Mars Express, an international scientific team led by the Institut de Planétologie et d'Astrophysique from Grenoble has recently achieved a significant advance in the debate about the geological nature of the circumpolar lowlands of Mars' northern hemisphere.
MARSIS is a low frequency sounding radar on board the European Mars Express mission. This instrument has the ability to deeply probe the Martian subsurface, down to a few kilometres under the polar icecaps. It is by studying Mars' surface radar reflectivity (the intensity of the first reflected radar echo) that a global map of the dielectric constant could be drawn. This constant directly depends on the composition and physical properties of the first tens of metres of the subsurface and thus on the geological nature of the terrain.
Map of Mars' northern (a, c) and southern (b) hemispheres between the 30° latitude and the poles, displayed in polar stereographic projection. The blue-red colour scale represents the dielectric constants measured by MARSIS. The low values (blue) are best explained by low-density materials and/or the presence of water ice, while high values (red) indicate the presence of dense volcanic materials. The contour-line indicating the presence of more than 10% water (water equivalent hydrogen or WEH) in the first metre and the one giving the theoretical stability limit of ice are also drawn on these maps. The solid and hash lines (lower figure) show the area delimited by the shoreline of the hypothetical ocean ("Oceanus Borealum"; "Deuteronilus" and "Arabia").
Mars Orbiter Laser Altimeter (MOLA) topographical measurements are shown in shaded-relief.
New analysis of data sent back by the SPICAM spectrometer on board ESA's Mars Express spacecraft has revealed for the first time that the planet's atmosphere is supersaturated with water vapour.
The atmosphere of Mars holds 10,000 times less water vapour than that of Earth. However, water vapour is a very dynamic trace gas, and one of the most variable atmospheric constituents on Mars.
Under normal conditions, water vapour condenses around tiny dust particles when the atmospheric temperature drops below a certain "dew point". The atmosphere is then said to be "saturated". However, when condensation nuclei are too rare, condensation is impeded, leaving amounts of excess water vapour. We are in a regime of "supersaturation".
Until now, it was generally assumed that such supersaturation cannot exist in the cold Martian atmosphere. However, data from the SPICAM spectrometer have revealed that supersaturation occurs frequently in Mars' atmosphere–at least during spring and summer in the northern hemisphere.
Extremely high levels of supersaturation were found on Mars, up to 10 times greater than those found on Earth. This discovery challenges our understanding of the phenomena controlling the Martian water cycle and has major consequences for the evolution of the Martian atmosphere.
The water cycle in the atmosphere of Mars can be described as follows:
- Heat from the Sun impacting upon surface ice (for example, the Polar Caps) causes water molecules (H2O) to sublimate and be released into the atmosphere.
- These water vapour molecules are transported by winds to higher altitudes where, in the presence of dust aerosols, they condense to clouds. When there are too few dust aerosols, condensation is impeded, leaving substantial amounts of water vapour, i.e. the atmosphere is supersaturated.
- Supersaturated water vapour is carried high in the atmosphere where it is affected by photodissociation; solar radiation splits the water vapour molecules into the constituent hydrogen and oxygen atoms, which can then escape into space.
Credits ESA/AOES Medialab
The relative abundance of liquid water on the Martian surface through time, as well as its climate history, have been derived from the analyses of alteration minerals discovered by OMEGA.
Substantial quantities of liquid water must have been stably present in the early history of Mars, as shown by the presence of 'hydrated' minerals ('phyllosilicates' or clay) on some very old areas of Mars' surface (>= 4 billion years).
OMEGA findings at last brought proofs that Mars had a "hot and humid" period shortly after its formation.
The discovery of these clays as well as the presence of hydrated sulphates enable to rewrite the history of the planet's evolution: the so-called 'Phylosian' period, since the formation of the planet until about 4 billion years when liquid water was present in abundance. This period was interrupted by a global climate change, probably linked to the loss of internal magnetic field, which was followed by a period called 'Theiikaien' corresponding to the sulphates when water was present only occasionally and under very acid form. Then the following 3.5 billion years correspond to an anhydrous period when Mars probably had a climate similar to nowadays.
In this HRSC camera 3D perspective view of the Marwth Vallis area (shades of grey), OMEGA has identified areas rich in phyllosilicates (clays, in blue on the image) which are water-rich minerals. These are preferentially on very cratered areas, thus very old. Their absence at the bottom of the channel as well as its opening suggests that when this channel was formed, the climate conditions did not enable the formation of these clays anymore.
The nature of polar caps has been identified
Early during the mission, the mapping and spectral analyses of the perennial (during summer) south polar cap carried out by OMEGA enabled to understand its nature. It is made of a large two to three-kilometre-deep water glacier, covered during summer by a thin layer of carbon dioxide (CO2) ice. Quantitatively, this result signifies that the south polar cap (but also the north cap) constitutes an important water reservoir, and thus does not constitute a CO2 reservoir.
OMEGA observed the southern polar cap of Mars on 18 January 2004, as seen on all three bands. The right one represents the visible image, the middle one the CO2 (carbon dioxide) ice, and the left one the H2O (water) ice.
ASPERA enabled to measure Mars' atmospheric escape.
ASPERA showed that the solar wind penetrates deep in Mars' ionosphere down to 270 km of altitude above the surface. This deep penetration provokes a direct interaction between the solar wind ions and Mars' ionosphere ions, thus sweeping Mars' ions and inducing an escape mechanism of the Martian atmosphere.
Solar wind ions (in blue) penetrate through Mars magnetosphere limit (in green) which induces interactions between these 2 components and sweeps Martian ions in the interplanetary medium (called escape mechanism process)
Published in Solar wind-induced atmospheric erosion at Mars: First results from ASPERA-3 on Mars Express, Lundin et al., Science, Vol. 305. no. 5692, pp. 1933 - 1936, doi:10.1126/science.1101860, 2004
Mars Express observes aurorae and nightglow on the Red Planet
The SPICAM instrument on boaad MEX brought out a nocturnal aurorae phenomenon in Mars' high atmosphere. These light emissions are attributed to the recombination of N and O to form NO molecule. The proposed mechanism is that on the dayside nitric oxides are photo-dissociated by solar UV photons, and nitric as well as oxygen atoms migrate toward the nightside. Then they can recombine to form NO molecule while emitting photons which constitute nocturnal aurorae observed by SPICAM. The same mechanism was observed on Venus. Moreover, it seems that the areas where these aurorae have been observed correspond to areas where the crustal magnetic field was mapped by Mars' Global Surveyor probe. This magnetic field results from the magnetization of Martian crust rocks during the period when the planet had an intense bipolar magnetic field. Up to now, about ten events have been identified in the data set.
An artist's impression of how the aurorae may look to an observer orbiting on the nightside of Mars.
Rare high-altitude clouds found on Mars
The first unambiguous observation of CO2 ice clouds in the atmosphere of Mars was reported by the OMEGA team. The nature of these clouds was identified based on the detection of a specific spectral signature in the near-infrared. Such a discovery is supported by complementary observations by the SPICAM instrument.
This image composite shows the carbon-dioxide-ice (CO2) cloud detected by OMEGA imaging spectrometer on 12 June 2004, during spring in the northern hemisphere. At that time, Mars Express was flying at more than 2000 km over the surface of the planet. The cloud was situated at 80 km altitude.
The four images of the cloud were taken at four distinct wavelengths. The 4.26 micron image (third from the left) allowed a clear and unambiguous spectral detection of the cloud. Interestingly, while the cloud itself only appeared at in the 0.5 and 4.26-micron images, its shadow, which is located 100 km southwest, remained visible at all wavelengths covered by OMEGA.
The opacity of this cloud is estimated to be greater than 0.5, corresponding to a 40 % dimming of the sunlight. The size of the cloud particles is 1.5 microns (1.5/1000 of a millimetre).
Credits ESA/OMEGA team
Study of ozone in the atmosphere of Mars
Ozone is one of the most reactive species in the Martian atmosphere. It controls the UV flux that reaches the ground, thus the habitability of the planet.
Nevertheless, on Mars the quantity of ozone is much lower than on Earth, and its protection effect is therefore minor.
Thanks to the recorded SPICAM UV spectra, the global climatology of ozone on Mars is retrieved for the first time with spatial and temporal coverage. A good overall agreement is obtained comparing SPICAM data to predictions of a Chemical General Circulation Model. These results will help further understanding of the dynamics and chemistry of Mars' atmosphere.
Evolution on one seasonal cycle of ozone column according to the latitude.
On the left, measured by SPICAM UV and on the right, calculated by the 3D model (the Solar Longitude (Ls): one orbit of Mars around the Sun)
Results presented during the Seventh International Conference on Mars, in July 2007 at the California Institute of Technology ("Caltech") in Pasadena.
Study of the water vapour and the water cycle
The Martian water cycle is one of the main cycles that control the Martian atmosphere. Recent observations have shown a highly spatial and temporal variability especially concerning the Polar Regions.
A water vapour emission is observed at Ls (the Solar Longitude (Ls): one orbit of Mars around the Sun) around 120, corresponding to tha similar effect, is observed during spring in the southern hemisphere, at Ls around 300 (half a year later).
The water vapour abundance is strongly correlated to the temperature cycle.
Distribution of water vapour in Mars atmosphere for about two Martian years according to the latitude measured by SPICAM.
Results presented during Mars Water cycle workshop, Paris 2008
Mars Express zeros in on erosion features
Mars Express has uncovered geological evidence suggesting that some depositional process, revealed by erosion, has been at work on large scales in the equatorial regions of the planet.
The evidence comes from the mineralogical composition of the Aram Chaos region. Data from the OMEGA instrument have revealed that this region shows a significant amount of sulphates and ferric oxides. The latter have been uncovered by erosion before dropping to the base of the cliffs.
Similar residual deposits enriched in ferric oxides, overlying a layered formation containing both ferric oxides and sulphates, have been observed by the Opportunity rover in Meridiani Planum, suggesting a common formation process.
This map shows the Aram Chaos region of Mars - a crater 280 km in diameter lying almost directly on the Martian equator where the OMEGA instrument found mineralogical evidence for large-scale deposits of ferric oxides (commonly known as 'rust' on Earth) and sulphates.
Fluviatile valleys on Mars
HRSC stereoscopic images provide a very precise retrieval of the topography (3D image) of Mars' surface. Applied to old fluviatile valleys, it measures the depth of the valleys, to draw automatically their position (blue lines) as well as the different hydrographic bassins (in colour) as can be done on Earth. The valleys are all directed along the direction of the slope as expected for rivers, and all in the direction of the main canyon.
HRSC 3D and 2D images of Echus Chasma canyon
Enormous volume of ice stored in Mars' polar caps
MARSIS subsurface radar data (Mars Express/ESA probe) enabled to map the bottom of Mars' south polar cap. This international study, to which scientists from the Laboratoire de Planétologie de Grenoble participated, enabled to evaluate the volume of water ice, stored in the polar cap, to 1.6 million km³.
Depth of Mars' south polar cap - LPG/ASI/ESA