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Publication archive

We report the first detection in the atmosphere of Mars of the nightside O2(a1Delta_g) emission at 1.27 µm from limb observations of the OMEGA imaging spectrometer on board Mars Express (MEX). The emission, detected in three cases out of 40 observations, is due to recombination in a downwelling air parcel of O atoms produced by photodissociation of CO2 on the dayside in the upper atmosphere (O + O + M -> O2* + M), and not from ozone UV photodissociation, as is often seen on the dayside. Observed vertical profiles and total retrieved vertical intensities are compared with models. When detected, the emission is 10 times larger than previous predictions, at ~240 kR. This can be explained in the frame of a general circulation model (GCM) of Mars. As predicted by the GCM, all positive observations were obtained at high latitudes, during the winter night. The model is validated, which simulates the large Hadley cell characterizing the meridional circulation, ascending from the summer pole and descending to the winter pole. This new emission is tracing uniquely a downward advection transport mechanism, and therefore its detailed study will provide important constraints on the overall aeronomy and dynamics of Mars. The impact on long-term stability of methane is examined. It is found that recycling through the mesosphere will not decrease significantly the overall lifetime of CH4 (~300 years), because the descent of air is confined to high latitudes and winter seasons. These observations are demonstrating a new diagnosis of the aeronomy and atmospheric dynamics of Mars.
Published: 09 March 2012
A number of observations suggest that an extended ocean once covered a significant part of the Martian northern hemisphere. By probing the physical properties of the subsurface to unprecedented depth, the MARSIS/Mars Express provides new geophysical evidences for the former existence of a Late Hesperian ocean. The Vastitas Borealis formation, located inside a putative shoreline of the ancient ocean, has a low dielectric constant compared with that of typical volcanic materials. We show that the measured value is only consistent with low-density sedimentary deposits, massive deposits of ground-ice, or a combination of the two. In contrast, radar observations indicate a distribution of shallow ground ice in equilibrium with the atmosphere in the south polar region. We conclude that the northern plains are filled with remnants of a late Hesperian ocean, fed by water and sediments from the outflow channels about 3 Gy ago.
Published: 19 January 2012
Clay minerals, recently discovered to be widespread in Mars's Noachian terrains, indicate long-duration interaction between water and rock over 3.7 billion years ago. Analysis of how they formed should indicate what environmental conditions prevailed on early Mars. If clays formed near the surface by weathering, as is common on Earth, their presence would indicate past surface conditions warmer and wetter than at present. However, available data instead indicate substantial Martian clay formation by hydrothermal groundwater circulation and a Noachian rock record dominated by evidence of subsurface waters. Cold, arid conditions with only transient surface water may have characterized Mars's surface for over 4 billion years, since the early-Noachian period, and the longest-duration aqueous, potentially habitable environments may have been in the subsurface.
Published: 03 November 2011
The vertical distribution of water vapor is key to the study of Mars' hydrological cycle. To date, it has been explored mainly through global climate models because of a lack of direct measurements. However, these models assume the absence of supersaturation in the atmosphere of Mars. Here, we report observations made using the SPICAM (Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars) instrument onboard Mars Express that provide evidence of the frequent presence of water vapor in excess of saturation, by an amount far surpassing that encountered in Earth's atmosphere. This result contradicts the widespread assumption that atmospheric water on Mars cannot exist in a supersaturated state, directly affecting our long-term representation of water transport, accumulation, escape, and chemistry on a global scale.
Published: 30 September 2011
The origin of the Martian moons, Phobos and Deimos, is still an open issue: either they are asteroids captured by Mars or they formed in situ from a circum-Mars debris disk. The capture scenario mainly relies on the remote-sensing observations of their surfaces, which suggest that the moon material is similar to outer-belt asteroid material. This scenario, however, requires high tidal dissipation rates inside the moons to account for their current orbits around Mars. Although the in situ formation scenarios have not been studied in great details, no observational constraints argue against them. Little attention has been paid to the internal structure of the moons, yet it is pertinent for explaining their origin. The low density of the moons indicates that their interior contains significant amounts of porous material and/or water ice. The porous content is estimated to be in the range of 30-60% of the volume for both moons. This high porosity enhances the tidal dissipation rate but not sufficiently to meet the requirement of the capture scenario. On the other hand, a large porosity is a natural consequence of re-accretion of debris at Mars' orbit, thus providing support to the in situ formation scenarios. The low density also allows for abundant water ice inside the moons, which might significantly increase the tidal dissipation rate in their interiors, possibly to a sufficient level for the capture scenario. Precise measurements of the rotation and gravity field of the moons are needed to tightly constrain their internal structure in order to help answering the question of the origin.
Published: 26 August 2011
CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) near-IR spectroscopic imaging of the Mars atmospheric limb supports vertical profiling of aerosol (ice and dust) and gas [H2O, CO, CO2, O2(1_Delta_g)] constituents versus season (Ls), latitude, and (to a limited degree) longitude. These CRISM limb observations are obtained approximately every two months (15° Ls), over a full range of sunlighted latitudes for two MRO (Mars Reconnaissance Orbiter) orbits centered on equatorial longitudes of 100W and 300W. Daylight limb spectra indicate strong 1.27 µm atmospheric emission from the excited singlet delta of molecular oxygen, associated with photolysis of Mars atmospheric ozone. Limb observations extending to un-illuminated, polar night latitudes present a new source of O2(1_Delta_g) emission at higher altitudes (40-55 km), associated with three body recombination of atomic oxygen [O+O+CO2 -> O2(1_Delta_g) +CO2]. This nightglow requires strong poleward supply of atomic oxygen, produced from photolysis of CO2 at sunlighted latitudes and transported at high altitudes (above 70 km) into polar night altitudes of 40-60 km. CRISM limb observations indicate distinctive latitudinal and longitudinal distributions of this polar nightglow that evolve over the Feb-Aug 2010 (Ls=50-140°) period of observations for the southern winter. New observations include planned full orbit mapping (12 orbits) in August 2010 to characterize these spatial variations in more detail. Key comparisons with co-located MCS (Mars Climate Sounder) temperature and aerosol profile retrievals and LMD (Laboratoire Météoroligie Dynamique) GCM photochemical simulations provide new insights into poorly constrained meridional transport into polar winter latitudes on Mars.
Published: 02 September 2010
The composition of the ancient martian crust is a key ingredient in deciphering the environment and evolution of early Mars. We present an analysis of the composition of large craters in the martian northern plains based on data from spaceborne imaging spectrometers. Nine of the craters have excavated assemblages of phyllosilicates from ancient, Noachian crust buried beneath the plains' cover. The phyllosilicates are indistinguishable from those exposed in widespread locations in the southern highlands, demonstrating that liquid water once altered both hemispheres of Mars.
Published: 25 June 2010
The eccentric orbit of Mars Express allows some close encounters with PHOBOS. Four observations were organized up to August 11, 2004. The spacecraft was put in a fixed inertial position, and Phobos was scanned from the orbital motion, crossing the slit of SPICAM UV imaging spectrometer in a few seconds. The distance was from 150 to 1900 km. Along the slit, five FOV of 10 x 1.3 arcmin each recorded the UV spectrum (110-310 nm, resolution 1.5 nm) of scattered solar light, resulting in 30 to 50 independent UV spectra at each encounter, and giving an unprecedented spatial resolution in UV. From the absolute calibration of SPICAM with star observations, the albedo may be determined as a function of wavelength and geography. Albedo markings were search for. The UV color (wavelength trend in the range 200-320 nm) was determined.Comparisons with previous measurements (in particular HST) will be discussed, with potential implications for mineralogy of Phobos.
Published: 11 November 2004

Abstract No. 1832

As a complement to Mars observations, Phobos spectral imaging was implemented in order to acquired compositional mapping with the prime objective to answer to the following questions:

  1. Is Phobos a "primitive" (undifferentiated) body, or is its mass sufficient for this small body to have suffered some degree of internal differentiation, so as to exhibit surface compositional variations reflecting variation with depth?
  2. Can one detect surface material containing either volatile or organic compounds ?
We will present an overview of the results acquired, and discuss them in terms of planetary differentiation.

Published: 10 March 2008

Abstract No. 2195

Of the many previous hypotheses concerning the origin of Phobos' grooves, most authorities agree that their formation is in some way connected with the creation of Stickney crater, at nearly 10 km diameter the largest crater on Phobos [1,2,3]. The principal argument for the Stickney association has been that the grooves form a pattern that is approximately radial to Stickney [1,2]. However, such hypotheses were based on incomplete mapping of the satellite, the largest poorly-imaged area being adjacent to Stickney's western rim. Much of the unknown region has now been imaged by HRSC, and we have assembled a new groove map from this and all other available imagery. The impression of grooves radial to Stickney can be seen to be an artefact of the previous coverage. East of Stickney this idea can be sustained, but west of it the pattern is tangential to the crater. The satellite-wide groove pattern can be seen to be centred not at Stickney, but at the leading apex of Phobos in its orbit (i.e. 90° long., 0° lat.). Groove orientations are quite independent of Stickney and bear no relation to it.

Published: 13 March 2006
The determination of the ephemeris of the Martian moons has benefited from observations of their plane-of-sky positions derived from images taken by cameras onboard spacecraft orbiting Mars. Images obtained by the Super Resolution Camera (SRC) onboard Mars Express (MEX) have been used to derive moon positions relative to Mars on the basis of a fit of a complete dynamical model of their motion around Mars. Since, these positions are computed from the relative position of the spacecraft when the images are taken, those positions need to be known as accurately as possible. An accurate MEX orbit is obtained by fitting two years of tracking data of the Mars Express Radio Science (MaRS) experiment onboard MEX. The average accuracy of the orbits has been estimated to be around 20-25 m. From these orbits, we have re-derived the positions of Phobos and Deimos at the epoch of the SRC observations and compared them with the positions derived by using the MEX orbits provided by the ESOC navigation team. After fit of the orbital model of Phobos and Deimos, the gain in precision in the Phobos position is roughly 30 m, corresponding to the estimated gain of accuracy of the MEX orbits. A new solution of the GM of the Martian moons has also been obtained from the accurate MEX orbits, which is consistent with previous solutions and, for Phobos, is more precise than the solution from the Mars Global Surveyor (MGS) and Mars Odyssey (ODY) tracking data. It will be further improved with data from MEX-Phobos closer encounters (at a distance less than 300 km). This study also demonstrates the advantage of combining observations of the moon positions from a spacecraft and from the Earth to assess the real accuracy of the spacecraft orbit. In turn, the natural satellite ephemerides can be improved and participate to a better knowledge of the origin and evolution of the Martian moons.
Published: 02 April 2008
Aims. New astrometric measurements for Phobos are reported on the basis of 69 SRC (Super Resolution Channel) images obtained during 28 Mars Express Phobos flybys executed between 2004 and 2007. Methods. The measurements have been made using a newly developed technique that involves positional measurements of surface control points and verification of camera pointing by background stars. Results. The astrometric positions are in excellent agreement with currently available Phobos orbit models. However, we find remaining systematic offsets of 1.5-2.6 km such that Phobos is ahead of its predicted position along the track. Conclusions. Our observations will be a basis for further improvements in the Phobos ephemeris. The methods that we have developed will be useful for the astrometric tracking of planetary or asteroidal targets and spacecraft optical navigation in future planetary missions.
Published: 25 February 2010
We present new ephemerides of Phobos and Deimos that are fit to observations from 1877 to 2005 and include recent spacecraft observations by Mars Global Surveyor and Mars Express. In contrast to earlier models, this is the first completely numerical one. In particular, the tidal effects have been modeled by the tidal bulge raised by each moon on the planet, instead of fitting secular accelerations in the satellite longitudes. This partly avoids absorbing the Deimos observational errors in its related tidal acceleration. Moreover, applying this model to other systems will be easier. Our estimate of the Martian dissipation is Q = 79.91±0.69 (1sigma-formal error) when assuming k2 = 0.152 for the Martian Love number and GmPh= 0.68 X 106 m3/s2 for the Phobos mass. We also report the possibility of fitting the Phobos oblateness gravity field. We suspect a non-uniform density for Phobos or a bias in either the observations or the Martian gravity field. A FORTRAN subroutine that computes the Martian moons' ephemerides is available on request.
Published: 04 April 2007
Observations of Phobos and Deimos, carried out by the SRC (Super Resolution Channel) on the Mars Express spacecraft between May 2004-April 2005, were used to determine the center-of-figure positions of the two Satellites with accuracies of 0.5-5 km (Phobos) and 1.0 km (Deimos). We find that the Phobos and Deimos orbit predictions from NASA-JPL (Jet Propulsion Laboratory) and ESA-ESOC (European Space Operation Center) differ substantially among each other and also do not agree with the actually observed positions of the satellites. Hence, our new astrometric data may motivate new efforts for Phobos and Deimos orbit modeling.
Published: 01 March 2006
A new independent control point network for Phobos was computed from image data obtained by the SRC (Super Resolution Channel) on board the European Mars Express Mission. The network solution includes 3D coordinates of 665 surface control points and was used to observe the forced libration amplitude of Phobos. Based on the network control points a spherical harmonic function model to degree and order 17 was derived, from which volume, bulk density and moments of inertia were computed. The modeled forced libration amplitude agrees to our observation within the error bands, indicating a homogeneous mass distribution for Phobos. To bring both values into exact agreement with the observations, different mass distribution models were applied. It appears that the amplitude is relatively insensitive to a simple two-layer density model.
Published: 27 August 2009
Phobos flyby images obtained by the High Resolution Stereo Camera (HRSC) and the Super Resolution Channel (SRC) onboard the Mars Express spacecraft were used to produce a global Digital Terrain Model and orthoimage mosaics. We derived a set of Phobos topographic image maps, which are combined into an atlas that consists of four quadrangles on three map sheets at the scale of 1: 50,000. The lateral geometric accuracy of these maps of ± 20 m is more than four times better than that of past products. They are based on a shape model with 0.52° × 0.52° grid spacing and show significantly more detail in comparison to previous data products.
Published: 02 November 2009
Ozone is a tracer of photochemistry in the atmosphere of Mars and an observable used to test predictions of photochemical models. We present a comparison of retrieved ozone abundances on Mars using ground-based infrared heterodyne measurements by NASA Goddard Space Flight Center's Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) and space-based Mars Express Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet measurements. Ozone retrievals from simultaneous measurements in February 2008 were very consistent (0.8 micron-atm), as were measurements made close in time (ranging from <1 to >8 micron-atm) during this period and during opportunities in October 2006 and February 2007. The consistency of retrievals from the two different observational techniques supports combining the measurements for testing photochemistry-coupled general circulation models and for investigating variability over the long-term between spacecraft missions. Quantitative comparison with ground-based measurements by NASA/GSFC's Infrared Heterodyne Spectrometer (IRHS) in 1993 reveals 2-4 times more ozone at low latitudes than in 2008 at the same season, and such variability was not evident over the shorter period of the Mars Express mission. This variability may be due to cloud activity.
Published: 16 September 2009
The detection of methane on Mars has revived the possibility of past or extant life on this planet, despite the fact that an abiogenic origin is thought to be equally plausible. An intriguing aspect of the recent observations of methane on Mars is that methane concentrations appear to be locally enhanced and change with the seasons. However, methane has a photochemical lifetime of several centuries, and is therefore expected to have a spatially uniform distribution on the planet. Here we use a global climate model of Mars with coupled chemistry to examine the implications of the recently observed variations of Martian methane for our understanding of the chemistry of methane. We find that photochemistry as currently understood does not produce measurable variations in methane concentrations, even in the case of a current, local and episodic methane release. In contrast, we find that the condensation-sublimation cycle of Mars' carbon dioxide atmosphere can generate large-scale methane variations differing from those observed. In order to reproduce local methane enhancements similar to those recently reported, we show that an atmospheric lifetime of less than 200 days is necessary, even if a local source of methane is only active around the time of the observation itself. This implies an unidentified methane loss process that is 600 times faster than predicted by standard photochemistry. The existence of such a fast loss in the Martian atmosphere is difficult to reconcile with the observed distribution of other trace gas species. In the case of a destruction mechanism only active at the surface of Mars, destruction of methane must occur with an even shorter timescale of the order of ~1 hour to explain the observations. If recent observations of spatial and temporal variations of methane are confirmed, this would suggest an extraordinarily harsh environment for the survival of organics on the planet.
Published: 07 August 2009
Edited by Dr. Angelo Pio Rossi and Dr. Olivier Witasse. This Special Issue of Planetary and Space Science contains 15 papers; the majority of which were presented at the European Mars Science and Exploration Conference (EMSEC) - Mars Express & ExoMars. There are several geoscience-related contributions covering volcanic, hydrologic, stratigraphic and geomorphologic investigations. The EMSEC conference was held 12-16 November 2007 at ESA ESTEC, Noordwijk, The Netherlands (see right-hand menu for conference programme).
Published: 16 July 2009
This ESA special publication is dedicated to the scientific investigations of Mars by Mars Express, giving a detailed overview of the scientific results of the mission so far.


Mars Express: Summary of Scientific Results
A. Chicarro, O.G. Witasse & A.P. Rossi
Scientific Instruments
HRSC: High Resolution Stereo Camera
G. Neukum, R. Jaumann and the Co-Investigator Team
OMEGA: Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité
J.-P. Bibring, Y. Langevin, F. Altieri et al.
MARSIS: Mars Advanced Radar for Subsurface and Ionospheric Sounding
J.J. Plaut, G. Picardi, T.W. Watters et al.
PFS: Planetary Fourier Spectrometer
V. Formisano, F. Angrilli, G. Arnold et al.
SPICAM: Spectroscopy for the Investigation of the Characteristics of the Atmospheric of Mars
J.-L. Bertaux, O. Korablev, D. Fonteyn et al.
ASPERA-3: Analyser of Space Plasmas and Energetic Neutral Atoms
R. Lundin, S. Barabash and the ASPERA-3 team
MaRS: Mars Express Radio Science Experiment
M. Pätzold, S. Tellmann, T. Andert et al.
Operations and Archiving
Mars Express Science Planning and Operations
R. Pischel & T. Zegers
Spacecraft and Payload Data Handling
J. Zender, F. Delhaise, C. Arviset et al.
Acronyms and Abbreviations279

Published: 16 June 2009
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