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The Magnetic Field of Mars: Past, Present and Future
Mario H. Acuña
NASA Goddard Space Flight Center
Greenbelt, MD 20771 USA
Presently, Mars possesses no intrinsic global magnetic field but experimental evidence
from Mars Global Surveyor suggests that one similar to that of Earth’s once existed in
its distant past. This evidence is based on the existence of strong crustal magnetization in
the ancient terrain of the highlands south of the dichotomy boundary. The deficiency in
magnetization in surrounding volcanic provinces and impact basins suggests that the crust
gained its magnetic remanence early on via an internal dynamo that became dormant
by the time of the last major impacts. This unique timing of the epoch of dynamo
cessation has important implications for the history of Mars atmosphere, ionosphere and
volatiles. Ion pick-up becomes a significant atmospheric loss mechanism operating for
billions of years, enhanced by the low gravity environment and corresponding large scale
height that allow the solar wind to interact with exospheric neutrals over an extended
volume of space. The MGS magnetic field measurements explored < 20% of the surface
at periapses ranging from 100 km to 400 km during the aerobraking and mapping orbits.
A major question raised by the observations is what is the true spatial scale of the intense
magnetic anomalies and missions such as ARES (Mars airplane) as well as others using
balloons are being proposed to resolve this major puzzle from low altitude platforms.
Although Mars Express does not measure magnetic fields directly, the activation of the
MARSIS experiment has revealed an unexpected source of scalar in-situ magnetic field
data that coupled to the complementary data acquired by the ASPERA and other MEX
investigations will allow a significant extension of the MGS and PHOBOS results.