Hot Jupiter Breezes: Time-dependent Outflows from Extrasolar Planets

TL;DR

This paper investigates the time-dependent magnetically controlled outflows from Hot Jupiters driven by stellar UV heating, revealing quasi-periodic variations in mass loss rates due to subsonic breeze solutions and their relation to system parameters.

Contribution

It introduces a model for time-variable, subsonic outflows from Hot Jupiters with magnetic fields, highlighting the impact of boundary conditions on flow variability and potential observational constraints.

Findings

Flow remains subsonic due to magnetic field configuration.

Outflow variability is quasi-periodic and linked to boundary conditions.

Flow time scales depend on the planetary sphere of influence.

Abstract

We explore the dynamics of magnetically controlled outflows from Hot Jupiters, where these flows are driven by UV heating from the central star. In these systems, some of the open field lines do not allow the flow to pass smoothly through the sonic point, so that steady-state solutions do not exist in general. This paper focuses on this type of magnetic field configuration, where the resulting flow becomes manifestly time-dependent. We consider the case of both steady heating and time-variable heating, and find the time scales for the corresponding time variations of the outflow. Because the flow cannot pass through the sonic transition, it remains subsonic and leads to so-called breeze solutions. One manifestation of the time variability is that the flow samples a collection of different breeze solutions over time, and the mass outflow rate varies in quasi-periodic fashion. Because the flow is subsonic, information can propagate inward from the outer boundary, which determines, in part, the time scale of the flow variability. This work finds the relationship between the outer boundary scale and the time scale of flow variations. In practice, the location of the outer boundary is set by the extent of the sphere of influence of the planet. The measured time variability can be used, in principle, to constrain the parameters of the system (e.g., the strengths of the surface magnetic fields).