- Copyright © 2003 Society of Exploration Geophysicists
The primary objective of the Mars Global Surveyor (MGS) Magnetic Field Investigation, which began in 1997, is to establish definitively the nature of the magnetic field of Mars. Sixteen prior missions to the planet by the United States and the former Soviet Union were not able to answer the fundamental question: Is there a magnetic field of internal origin at Mars as there is on Earth?
Following the arrival of MGS at Mars in September 1997, vector magnetic field observations were acquired from more than 1000 elliptical orbits with the point of closest approach to the planet ranging from 85 to 170 km above the surface. Large volumes of vector data have also been acquired from more than 10 000 orbits in a fixed plane at the 400-km altitude circular mapping orbit. It is expected that the spacecraft and magnetic field instruments will remain operational in this orbit through 2008.
MGS uses two magnetic field sensors at the edge of the solar arrays, about 4.5 m from the center of the spacecraft, and about 9 m from each other. The arrays were designed to produce minimal fields (<0.25 nT) at the sensor. The accuracy of the measurements is determined from internal calibrations and by how well the variable spacecraft generated field is known in flight. Engineering data from the MGS power system and both magnetometers are input to a real-time model of the spacecraft magnetic field, which is then subtracted from the measurements to yield a final accuracy estimated at <1 nT per component. During the cruise phase the satellite was placed in a “rotisserie” mode, rolling slowly about the axis pointed at Earth. This is advantageous for magnetic field measurements because the roll of the spacecraft introduces a modulation in the two “spin-plane” components which is used to calibrate …