Properties of Mars' Dayside Low-Altitude Induced Magnetic Field and
Comparisons with Venus
Abstract
Mars and Venus have atmospheres but lack large-scale intrinsic magnetic
fields. Consequently, the solar wind interaction at each planet results
in the formation of an induced magnetosphere. Our work aims to compare
the low-altitude (< 250 km) component of the induced magnetic
field at Venus and Mars using observations from Pioneer Venus Orbiter
(PVO) and Mars Atmosphere and Volatile EvolutioN (MAVEN). The
observations from Mars are restricted to regions of weak crustal
magnetism. At Venus, it has long been known the vertical structure of
the induced magnetic field profiles have recurring features that enable
them to be classified as either magnetized or unmagnetized. We find the
induced field profiles at Mars are more varied, lack recurring features,
and are unable to be classified in the same way. The solar zenith angle
dependence of the low-altitude field strength at both planets is
controlled by the shape of the magnetic pileup boundary. Also, because
the ionospheric thermal pressure at Venus is often comparable to the
solar wind dynamic pressure, the induced fields are weaker than required
to balance the solar wind by themselves. By contrast, induced fields at
Mars are stronger than required to achieve pressure balance. Lastly, we
find the induced fields in the magnetized ionosphere of Venus have a
weaker dependence on solar wind dynamic pressure than the induced fields
at Mars. Our results point to planetary properties, such as planet-Sun
distance, having a major effect on the properties of induced fields at
nonmagentized planets.