In the lower image, a linear reflector nearly parallel to the surface is seen embedded in the arcs. This reflection may be coming from the floor of the basin. The time delay to the linear reflector suggests a depth of 1.5-2.5 km.


 
This topographic map, based on Mars Orbiter Laser Altimeter data, shows the MARS Express groundtracks and the arc structures detected by MARSIS that are interpreted to be part of a buried impact basin about 250 km in diameter. The topographic relief represented in the image is 1 km, from low (purple) to high (red). The projected arcs are shown in red for orbit 1892 and white for orbit 1903. There is no obvious feature in the surface topography that corresponds to the buried feature identified with MARSIS data.


 
This MARSIS radargram image (top) shows data from the subsurface of Mars in the layered deposits that surround the north pole. The lower image shows the position of the ground track on a topographic map of the area based on Mars Orbiter Laser Altimeter data. The images show an area 458 km wide.

The MARSIS echo trace splits into two traces to the right of centre, at the point where the spacecraft's groundtrack crosses from the smooth plains onto the elevated layered deposits on the right.

The upper trace is the echo from the surface of the deposits, while the lower trace is interpreted to be the boundary between the lower surface of the deposits and the underlying material.

The strength of the lower echo suggests that the intervening material is nearly pure water ice. The time delay between the two echoes reaches a maximum of 21 microseconds at the right of the image, corresponding to a thickness of 1.8 km of ice. The total elevation difference shown in the topographic map is about 2 km, between the lowest surface (magenta) and the highest (orange).



Release date: 30 November 2005