The top figure shows a view of Mercury from above its north pole and the
trajectories along which Magnetometer observations were made by the
Mariner 10 mission (blue) and the MESSENGER spacecraft (tan). The
MESSENGER data from the mission’s second Mercury flyby provide the only
data to date from the planet’s western hemisphere and are therefore key to
constraining the geometry of the planet’s internal magnetic field. The
bottom figure graphs the magnetic field strengths measured during
MESSENGER’s first (blue) and second (orange) Mercury flybys, with a
striking similarity in the maximum field strength measured during both
encounters. The observations are displayed versus distance along the
planet-Sun line; closest approach (CA) occurred at about three-fourths of
a Mercury radius to the night side of the planet. The magnetopause and
bow shock crossings occurred where they were expected, so for this
comparison the distance scale for flyby 1 has been stretched so that these
boundaries are coincident. Near CA, the flyby 2 data yield a field
strength that is only a few percent lower than that obtained from flyby 1
observations. This remarkably close agreement means that the planetary
magnetic moment is very nearly centered and is strongly aligned with the
rotation axis, to within a tilt of 2°. This result favors models for
Mercury’s magnetic field generation that predict a magnetic moment aligned
with the rotation axis.
Date Acquired: January 14 and October 6, 2008
Instrument: Magnetometer (MAG)
These images are from MESSENGER, a NASA Discovery mission to conduct the
first orbital study of the innermost planet, Mercury. For information
regarding the use of images, see the MESSENGER image use policy.