Planetary Magnetism as a Factor of Exoplanet Habitability
Discovering life outside the solar system using telescopic observations is the ultimate goal of planetary science. However, while we wait for the next generation of telescopes to come online, we can make use of current data to assess the habitability of a planet using a variety of planetary and astronomical features. This will assist in determining optimal targets for near-future observations of planetary atmospheres.
One requirement for habitability is liquid water. Thus far this requirement has only been applied to determining the location of the circumstellar habitable zone (CHZ). However, a strong dipolar magnetic moment may play a significant role in the maintenance of surface liquid water. Mars’s weak magnetic field is thought to have contributed to the loss of atmosphere and ultimately the absence of liquid water on its surface today. Furthermore, the high D/H abundance ratio in the atmosphere of Venus (120 times that on Earth) indicates large amounts of water loss, potentially attributable to the lack of substantial magnetic field. On the other hand, Earth’s geodynamo appears to have been remarkably continuous since its inception.
This research investigated the dipolar magnetic moment of habitable planets in order to determine whether their magnetospheric protection is sufficient to shield the surface (and the potential liquid water on it) from the effects of X-EUV radiation, coronal mass ejections, cosmic rays, stellar winds and stellar magnetic fields. We show it is likely that only a small fraction of CHZ planets have a sufficient dynamo to sustain liquid water on their surfaces.