Mars radar opens up a planet’s third dimension


Radar sounding is opening up a planet’s third dimension
 
Radar sounding is opening up the third dimension for planetary exploration. First tried on Mars, the technique’s success is prompting scientists to think of all the other places in the Solar System where they would like to use radar sounders.

Martian south polar layered deposits
 
South polar layered deposit (SPLD) on Mars.

The Mars Express radar experiment, MARSIS, was designed to penetrate deep and it has delivered on its promise. The above figure shows the base of the SPLD at the deepest recorded point of 3.7 km. In contrast, The Shallow Subsurface Radar (SHARAD) on NASA’s Mars Reconnaissance Orbiter designed as a high-resolution radar for a maximum penetration of 1 km has difficulty detecting the SPLD base. The two complementary instruments work together to discover hidden martian secrets.

MARSIS sending signals and receiving echoes
 
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.

MARSIS completely deployed
 
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: 27 June 2008