Ambipolar Electric Field, Photoelectrons, and their Role in Atmospheric Escape From Hot-jupiters

TL;DR

This paper investigates how ambipolar electric fields and photoelectrons significantly enhance atmospheric escape in Hot-jupiters by increasing ion scale-height and mass-loss rates, drawing parallels with Earth's polar wind.

Contribution

It provides a simplified model quantifying the impact of polar wind effects on atmospheric escape in Hot-jupiters, highlighting their importance.

Findings

Ion scale-height can increase by a factor of 2-15 due to polar wind effects.

Atmospheric mass-loss rate can be underestimated without considering these effects.

Mass-loss can be at least an order of magnitude higher when including polar wind influences.

Abstract

Atmospheric mass-loss from Hot-jupiters can be large due to the close proximity of these planets to their host star and the strong radiation the planetary atmosphere receives. On Earth, a major contribution to the acceleration of atmospheric ions comes from the vertical separation of ions and electrons, and the generation of the ambipolar electric field. This process, known as the "polar wind", is responsible for the transport of ionospheric constituents to the Earth's magnetosphere, where they are well observed. The polar wind can also be enhanced by a relatively small fraction of super-thermal electrons (photoelectrons) generated by photoionization. We formulate a simplified calculation of the effect of the ambipolar electric field and the photoelectrons on the ion scale-height in a generalized manner. We find that the ion scale-height can be increased by a factor of 2-15 due to the polar wind effects. We also estimate a lower limit of an order of magnitude increase of the ion density and the atmospheric mass-loss rate when polar wind effects are included.