AN IONOSPHERIC SOUNDER FOR THE MARS LANDERS

The planet Mars has been visited in the past by orbital probes and lan ders to study the atmosphere and the ground. But despite these numerou s missions, more than 20 years ago, many parameters and phenomena are not known at this time. The large possibilities given by new technolog ies, in terms of weight and power consumption, allow the realization o f new experiments at the surface of Mars. The aim is to propose the in stallation of a bottomside ionospheric sounder. This instrument will c ontribute to our scientific understanding of Mars. It will answer one of the main scientific objectives of the IMEWG (International Mars Exp loration Working Group) mission scenario: the characterization of the Martian upper atmosphere and its interaction with the solar wind. Iono spheric sounding is a well-known technique at the surface of the Earth which has proven to be very useful for the study of the lower ionosph ere. The principle is to transmit a radio pulse vertically and to meas ure the time which elapses before the echo is received. By varying the frequency of the pulse carrier wave, a plot can be obtained of echo d elay versus frequency. It gives information about the propagation medi um. The scientific objectives are described which can be achieved with such an experiment and the parameters which can be measured underlini ng the specificity of the Martian atmosphere are given. The theoretica l scientific background of this sounder is briefly described and, fina lly, its feasibility is discussed. Copyright (C) 1996 Elsevier Science Ltd