Radar’s icy echoes on Mars
The upper image of this composite is a ‘radargram’ from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board ESA’s Mars Express. It shows data from the subsurface of Mars in the water-ice-rich layered deposits that surround the south pole of the planet.
The lower image shows the position of the ground track of the spacecraft (indicated by a white line) on a topographic map of the area based on data from the MOLA laser altimeter on board NASA's Mars Global Surveyor. The images are 1250 kilometers wide. A non-annotated version of the image can be found here. here.
The MARSIS radar echo trace splits into two traces on the left side of the image, at the point where the ground track crosses from the surrounding plains onto elevated layered deposits.
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. Near the image center, the bright lower echo abruptly disappears for unknown reasons. The time delay between the two echoes reaches a maximum of 42 microseconds left of center, corresponding to a thickness of 3.5 kilometres of ice. The total elevation difference shown in the topographic map is about 4 kilometres between the lowest surface (purple) and the highest (red).
Credits: NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team
This map shows the thickness of the south polar layered deposits of Mars, an ice-rich geologic unit that was probed by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board ESA’s Mars Express. A non-annotated version of the image can be found here.
The thickness of the layered deposits was determined by measuring the time delay between radar echoes from the surface and those from the lower boundary, or ‘bed’, of the deposits. The radar data indicate that the deposit, larger than than a big portion of Europe in area, is more than 3.7 kilometres thick in places, and that the material consists of nearly pure water ice with only a small component of dust.
The map was generated by comparing the elevation of the bed as determined by MARSIS with the high-resolution map of surface topography obtained by the Mars Orbiter Laser Altimeter (MOLA) aboard NASA’s Mars Global Surveyor. The thickness of the layered deposits is shown by colors, with purple representing the thinnest areas, and red the thickest.
The total volume of ice in the layered deposits is equivalent to a water layer 11 metres deep, if spread evenly across the planet. The boundary of the layered deposits was mapped by scientists from the U.S. Geological Survey. The dark circle in the upper center is the area pole-ward of 87 ° south latitude, where MARSIS data cannot be collected. The map covers an area 1670 by 1800 kilometres.
Credits: NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team/USGS