Mars Express orbiter instruments

Orbiter scientific payload
  • Surface/subsurface instruments
    • HRSC (High Resolution Stereo Camera)
    • OMEGA (Visible and Infrared Mineralogical Mapping Spectrometer)
    • MARSIS (Sub-surface Sounding Radar Altimeter)

  • Atmosphere/Ionosphere instruments
    • PFS (Planetary Fourier Spectrometer)
    • SPICAM (Ultraviolet and Infrared Atmospheric Spectrometer)
    • ASPERA (Energetic Neutral Atoms Analyser)

  • Radio link
    • MaRS (Mars Radio Science Experiment)

High Resolution Stereo Camera (HRSC)

The HRSC is imaging the entire planet in full colour, 3D and with a resolution of about 10 metres. Selected areas will be imaged at 2-metre resolution. One of the camera's greatest strengths will be the unprecedented pointing accuracy achieved by combining images at the two different resolutions. Another will be the 3D imaging which will reveal the topography of Mars in full colour.

"As the 2-metre resolution image is nested in a 10-metre resolution swath, we will know precisely where we are looking. The 2-metre resolution channel will allow us to pick out great detail on the surface," says Gerhard Neukum, HRSC Principal Investigator from Freie Universität Berlin, Germany.

OMEGA Visible and Infrared Mineralogical Mapping Spectrometer

OMEGA is building up a map of surface composition in 100 metre squares. It will determine mineral composition from the visible and infrared light reflected from the planet's surface in the wavelength range 0.5-5.2 microns. As light reflected from the surface must pass through the atmosphere before entering the instrument, OMEGA will also measure aspects of atmospheric composition.

"We want to know the iron content of the surface, the water content of the rocks and clay minerals and the abundance of non-silicate materials such as carbonates and nitrates," says Jean-Pierre Bibring, OMEGA PI from the Institut d’Astrophysique Spatiale, Orsay, France.

SPICAM Ultraviolet and Infrared Atmospheric Spectrometer

SPICAM is determining the composition of the atmosphere from the wavelengths of light absorbed by the constituent gases. An ultraviolet (UV) sensor will measure ozone, which absorbs 250-nanometre light, and an infrared (IR) sensor will measure water vapour, which absorbs 1.38 micron light.

"Over the lifetime of the mission, we should be able to build up measurements of ozone and water vapour over the total surface of the planet for the different seasons," says Jean-Loup Bertaux, SPICAM PI from the Service d'Aeronomie du CNRS, Verrières-le-Buisson, France.

Planetary Fourier Spectrometer (PFS)

The PFS is determining the composition of the Martian atmosphere from the wavelengths of sunlight (in the range 1.2-45 microns) absorbed by molecules in the atmosphere and from the infrared radiation they emit.

In particular, it will measure the vertical pressure and temperature profile of carbon dioxide which makes up 95% of the martian atmosphere, and look for minor constituents including water, carbon monoxide, methane and formaldehyde.

"We hope to get many, many measurements so that by taking the average of thousands we'll be able to see minor species," says Vittorio Formisano, PFS PI from Istituto Fisica Spazio Interplanetario, Rome, Italy.

ASPERA Energetic Neutral Atoms Analyser

ASPERA is measuring ions, electrons and energetic neutral atoms in the outer atmosphere to reveal the numbers of oxygen and hydrogen atoms (the constituents of water) interacting with the solar wind and the regions of such interaction.

Constant bombardment by the stream of charged particles pouring out from the Sun, is thought to be responsible for the loss of Mars's atmosphere. The planet no longer has a global magnetic field to deflect the solar wind, which is consequently free to interact unhindered with atoms of atmospheric gas and sweep them out to space.

"We will be able to see this plasma escaping the planet and so estimate how much atmosphere has been lost over billions of years," says Rickard Lundin, ASPERA PI from the Swedish Institute of Space Physics in Kiruna, Sweden.

Mars Radio Science Experiment (MaRS)

MaRS will use the radio signals that convey data and instructions between the spacecraft and Earth to probe the planet's ionosphere, atmosphere, surface and even the interior.

Information on the interior will be gleaned from the planet's gravity field, which will be calculated from changes in the velocity of the spacecraft relative to Earth. Surface roughness will be deduced from the way in which the radio waves are reflected from the Martian surface.

"Variations in the gravitational field of Mars will cause slight changes in the speed of the spacecraft relative to the ground station, which can be measured with an accuracy of less than one tenth the speed of a snail at full pace," says Martin Pätzold, MaRS PI from Köln University, Germany.

MARSIS Sub-Surface Sounding Radar Altimeter

MARSIS will map the sub-surface structure to a depth of a few kilometres. The instrument's 40-metre long antenna will send low frequency radio waves towards the planet, which will be reflected from any surface they encounter.

For most, this will be the surface of Mars, but a significant fraction will travel through the crust to be reflected at sub-surface interfaces between layers of different material, including water or ice.

"We should be able to measure the thickness of sand deposits in dune areas, or determine whether there are layers of sediment sitting on top of other material," says Giovanni Picardi, MARSIS Principal Investigator from Universita di Roma 'La Sapienza', Rome, Italy. MARSIS will also study the ionosphere, as this electrically charged region of the upper atmosphere will reflect some radio waves.

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