An introduction—Geophysics: Doing it in space

Abstract

Missions to Mars have been fraught with failures. So the recent successes of Mars Pathfinder, Mars Global Surveyor (MGS), and Mars Odyssey are that much sweeter. Low altitude passes of MGS around the planet—a boon to magnetics—were serendipitous and actually occurred as a result of engineering malfunction. One of the solar panels did not open fully prior to intended aerobraking to circularize the orbit at its 400 km present altitude. Therefore the mission engineers allowed an elliptical orbit to continue for more than a year. This orbit brought the spacecraft close to the planet (about 100–170 km range) for a much longer period. For potential-field studies, these close passes meant increased signal as well as better spatial resolution. The initial excitement of the discovery of 400 nT bulls-eye anomalies was soon surpassed by bands of magnetic field variations exceeding 1500 nT. At these spatial scales, these values for Mars are equivalent to more than 10 times the magnetization of the Earth's crust. So far these spacecraft have provided enormous information at unprecedented resolution—ranging from camera images showing geomorphic features that allow comparisons with processes on Earth, topographic variations from laser altimeter, to the measurement of the gravity field. In the last few years we have begun to see publications dealing with the Mars geophysical data and their interpretation. Jack Connerney, a coauthor on one paper in this issue, has published about the possibility of plate tectonics on Mars. Good articles about the processing and use of satellite-derived gravity and satellite-acquired magnetics of the Earth are not new, but the industry and academia are using these data as a standard part of their work now. The information content is surprising and gratifying. An important aspect of much of the spaceborne data, whether from Earth or any of the planets/moons, …