Mars Express

Mars Express is the first mission of ESA (European Space Agency) to the red planet. It is also the first European mission to any planet. First "flexible-mission" in the scientific program of ESA, it was developed in record time: it took only 5 years from concept to launch. Using the technology developed for the Mars-96 and Rosetta missions at ESA, Mars Express answers fundamental questions that we ask ourselves about the geology of Mars, the atmosphere, the environment, the surface, the history of water and possible life on Mars. The mission was launched in 2003 and the spacecraft is still in orbit around Mars today.

The objectives of the mission are:

  • Search for subsurface water,
  • Global high-resolution photo-geology and mineralogical mapping,
  • Analysis of atmospheric composition and circulation,
  • Study of the Martian environment, including dynamical environmental processes,
  • Study of Mars’ gravity field in order to characterize the interior of the planet,
  • Deployment of a lander, Beagle 2, on the surface, to perform in-situ geological, mineralogical, and geochemical analyzes of selected rocks and soils at the landing site.
Credit: ESA

The Mars Express adventure began on June 2 2003, with the launch of the spacecraft by a Russian Soyuz-Fregat rocket from Baikonur. The duration of the journey was about seven months: Mars Express arrived at Mars in December 2003. The Beagle 2 lander was attached to one side of the spacecraft. The spacecraft went into orbit (Mars Orbit Insertion, December 25) 6 days after having released the lander (December 19). Beagle 2 landing on the surface of Mars did however not succeed. Nevertheless Mars Express was a success with seven scientific instruments in total onboard the orbiting spacecraft studying the Martian atmosphere, the planet's structure and geology.

One of the most interesting instrument in the frame of ESPaCE is the radio transponder. The Radio-Science experiment (MaRS) has measured Mars' gravitational field and its time variations, and allowed us to characterize the mass distribution inside Mars as well as the seasonal changes in the mass distribution in the atmosphere and icecaps. This experiment has no dedicated hardware. It uses the radio-links between the spacecraft and the Earth, sent out at the ESA large antennas (ESTRACK stations) of Perth (New Nortia, Australia), Madrid (Spain), as well as at the DSN (Deep Space Network) US antennas of Goldstone (California), Madrid (Spain), and Canberra (Australia). Since the Viking and Phobos 2 missions, the technology has advanced and Doppler shift measurements provided by Mars Express are ten times more accurate than those by the old space probes. It is therefore possible to get the precise spacecraft position and velocity measurements.

The spacecraft Mars Express has a very elongated orbit, which provides the opportunity to flyby by Phobos, the little moon of Mars. For radioscience, this allows determining the mass of Phobos by the interpretation of the Doppler tracking of the Mars Express spacecraft during a close flyby of the Martian moon. By compiling the mass and moment of inertia of Phobos, scientists can try to determine its origin, and what was its evolution.

The MEX spacecraft has not only been observed by the ESTRACK and DSN stations but as well using Very Long Baseline Interferometry (VLBI) tracking. Planetary Radio Interferometry and Doppler Experiment (PRIDE) does also provide accurate estimation of the state-vector of a spacecraft. The combination of both, the Doppler and ranging measurements from the ESTRACK and DSN stations with those of the VLBI stations will provide cross-checking at least and hopefully better estimations of the physical parameters wanted such as the mass and moments of inertia of Phobos.

The spacecraft Mars Express has a very elongated orbit, which provides the opportunity to flyby by Phobos, the little moon of Mars. Flybys allow us to get information on the interior of Phobos. As shown in our 3D animation at on “This animation shows MarsExpress flyby of the moon Phobos of Mars and the influence of the interior of Phobos on the flyby trajectory.”, the flyby trajectory depends on the interior mass repartition. The spacecraft Mars Express has performed several flybys with the objective to obtain the mass of Phobos and its moments of inertia. The study of moment of inertia and mass together with the knowledge of the volume of Phobos allows to get information on the interior density and mass repartition, and there with on Phobos’ origin.

ESA has covered the events on its own blog.

ESA websites of interest:

  1. Martian moons: Phobos, posted on the web on
  2. Mars-facing side of Phobos, taken from a distance of less than 200 km with a resolution of about seven meters per pixel, on 22 August 2004, on
  3. Close-up of Phobos acquired on 28 July 2008 by HRC on MarsExpress, on
  4. The Martian moons Phobos and Deimos, ESA’s Mars Express orbiter imaged the Martian moons Phobos and Deimos together on 5 November 2009, on
  5. Simulation of the Phobos flyby of 7 March 2010 showing the relative orbits of Phobos and Deimos and the Mars Express spacecraft, on
  6. Pioneering images of bot Martian moons, ESA’s Mars Express orbiter imaged the Martian moons Phobos and Deimos together on 5 November 2009, on
  7. Mars Express closest ever approach to Phobos on 3 March 2010, see and
  8. Images from the flyby of Phobos on 7 March 2010, released on 15 Mar 2010, see and

Further information can be found in:

  1. Lainey V., Dehant V., and Pätzold M., 2007, First numerical ephemerides of the two Martian moons., Astron. Astrophys., 465(3), pp. 1075-1084, DOI: 10.1051/0004-6361:20065466.
  2. Rosenblatt P., Lainey V., Le Maistre S., Marty J.C., Dehant V., Pätzold M., Van Hoolst T., Häusler B., 2008, Accurate Mars Express orbit to improve the determination of the mass and ephemeris of the Martian moons., Planet. Space Sci., 56(7), pp. 1043-1053, DOI: 10.1016/j.pss.2008.02.004.
  3. Andert T.P., Rosenblatt P., Pätzold M., Häusler B., Dehant V., Tyler G.L., and Marty J.C., 2010, Precise Mass Determination and the Nature of Phobos., Geophys. Res. Lett., 37, CiteID: L09202, DOI: 10.1029/2009GL041829.
  4. Rosenblatt P., 2011, The origin of the Martian moons revisited., Astron. Astrophys. Rev., 19(1), pp. 1-26, DOI: 10.1007/s00159-011-0044-6.
  5. Rambaux N., Castillo-Rogez J., Le Maistre S., and Rosenblatt P., 2012, Rotational motion of Phobos., Astronomy & Astrophysics, 548, id.A14, 11 pp., DOI: 10.1051/0004-6361/201219710.
  6. Rosenblatt P., and Charnoz S., 2012, On the Formation of the Martian Moons from a circum-martian accretion disk., Icarus, 221(2), pp. 806-815, DOI: 10.1016/j.icarus.2012.09.009.
  7. Le Maistre S., Rosenblatt P., Rambaux N, Castillo-Rogez J.C., Dehant V, and Marty J.C., 2013, Phobos interior from librations determination using Doppler and star tracker measurements., Planetary and Space Science, 85, pp. 106-122, DOI: 10.1016/j.pss.2013.06.015.
  8. Witasse O., Duxbury T., Chicarro A., Altobelli N., Andert T., Aronica A., Barabash S., Bertaux J.-L., Bibring J.-P., Cardesin-Moinelo A., Cichetti A., Companys V., Dehant V., Denis M., Formisano V., Futaana Y., Giuranna M., Gondet B., Heather D., Hoffmann H., Holmström M., Martin P., Matz K.-D., Montmessin F., Morley T., Mueller M., Manaud N., Neukum G., Oberst J., Orosei R., Pätzold M., Picardi G., Pischel R., Plaut J.J., Reberac A., Pardo Voss P., Roatsch T., Rosenblatt P., Remus S., Schmedemann N., Willner K., and Zegers T., 2013, Mars Express Investigations of Phobos and Deimos., Planetary and Space Science, in press, DOI: 10.1016/j.pss.2014.01.004.
  9. Pätzold M., Andert T., Jacobson R., Rosenblatt P., and Dehant V., 2014, Phobos: Observed bulk properties., Planetary and Space Science, in press, DOI: 10.1016/j.pss.2013.08.002.