Radar sounding of the Eastern Medusae Fossae Formation ... - Inaf

• Launched on June 2,2003.• ESA's first planetarymission.• Carries sevenexperiments, includingthe Italian radarMARSIS.• Will remain operationaluntil 2014.Mars Express

MARSIS• Mars Advanced Radar for Subsurfaceand Ionosphere Sounding (MARSIS)radar sounder is the first since Apollo17.• It transmits and receives through a 40m dipole, and it also receives througha 7 m monopole.• It operates at frequencies of 1.8, 3, 4and 5 MHz with a bandwidth of 1MHz.• The main scientific goal is to detectthe presence of solid or liquid waterin the subsurface of Mars.

Mars Reconnaissance Orbiter• Launched on August 12,2005.• NASA mission with highresolution sensors, tosearch for traces ofwater on the surface ofthe planet.• It has now beenextended until 2013.

SHARAD• Shallow Radar (SHARAD) is a radarsounder designed before MARSISwas launched.• It transmits and receives through a9 m dipole.• It operates at a frequency of 20MHz with a bandwidth of 10 MHz.• The main scientific goal is thedetection of dielectricdiscontinuities in the subsurface ofMars, and the interpretation ofthese discontinuities in terms ofpresence of ice, water, rock orregolith.

MARSIS and SHARAD• The Italian radar SHARAD isintended to be complementaryto MARSIS, obtaining highresolution sacrificingpenetration.• MARSIS was designed to map theglobal distribution of ice andwater in the subsoil.• SHARAD was born from theresults of MGS on the presenceof water near the surface inrecent times.

MARSIS vs. SHARAD

Radar Sounding of the Medusae FossaeFormation Mars: Equatorial Ice or Dry, Low-Density Deposits?Watters et al. 2007

Shallow radar (SHARAD) sounding observationsof the Medusae Fossae Formation, MarsCarter et al. 2009

Between Gordii Dorsum and Amazonis Mensa: MARSIS

Between Gordii Dorsum and AmazonisMensa: SHARAD (1)

Between Gordii Dorsum and AmazonisMensa: SHARAD (2)

Retrieving the dielectric properties of• Method taken fromPorcello et al. (1974)• The antenna cannot becalibrated• Ratio between Ps andPss is used• Simultaneousobservations at twofrequencies allowretrieval of loss tangentthe subsurface

A typical echo of MARSIS over the area

Results• Thickness– First layer: 750 / m– Second layer: 700 / m• Loss tangent– First layer: 0.01– Second layer: 0.003

Summary• Layering in the plains between Amazonis Mensa andGordii Dorsum has been observed by MARSIS and, to alesser extent, by SHARAD• This is the only place outside the PLD where MARSISdetects more than one subsurface discontinuity.• Although MARSIS coverage is still sparse, it seems thatthe two layers are either present or absent together.• Dielectric properties in the upper layer are compatiblewith those of dry rock• Dielectric properties in the second layer are compatiblewith those of very porous rock or regolith, or dirty ice.