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Mars Express: First global map of martian ionosphere   The principle of radar science used by MARSIS is based on the detection of radio waves reflected by boundaries between different materials. By analysis of these echoes, it is possible to deduce information about the kind of material causing the reflection, such as estimates of its composition and physical state.
Different materials are characterised by their ‘dielectric constant’, that is the specific way they interact with electromagnetic radiation, such as radio waves. When a radio wave crosses the boundary of different layers of material, an echo is generated and carries a sort of fingerprint from the specific materials. The MARSIS antenna booms here are seen receiving reflected signals. The red dotted line denotes the top of the ionosphere of Mars.  This figure is a map of the total electron content (TEC) in the Martian ionosphere, created with data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) onboard Mars Express. The vertical scale indicates latitude (y-axis) and the horizontal (x-axis) is for longitude.
Imagine yourself looking at Mars from space. If the whole planet were covered in darkness and your eyes could see the electrons in the ionosphere, this figure is what you would see. The brighter areas are areas of higher electron content.  This is an impression of the completely deployed MARSIS experiment on board ESA's Mars Express orbiter. Its two 20-metre booms and the 7-metre booms are sprung out and locked into place.
The MARSIS experiment will map the Martian sub-surface structure to a depth of a few kilometres. The instrument's 40-metre long antenna booms will send low frequency radio waves towards the planet, which will be reflected from any surface they encounter. Release date: 17 April 2008 |