Radiative Thrusters on Close-in Extrasolar Planets

TL;DR

This paper investigates how radiation absorption and reradiation by close-in exoplanets can produce a force affecting their orbits, potentially explaining observed correlations between orbital parameters and planetary surface gravity.

Contribution

It evaluates the impact of radiative thrusters on exoplanet orbital evolution and assesses their role in observed semi-major axis and surface gravity correlations.

Findings

Typical orbital changes are about 1% over planetary lifetimes.

Close-in and inflated planets could experience up to 5% orbital shifts.

Radiative thrusters are too weak to solely explain the observed correlation.

Abstract

The atmospheres of close-in extrasolar planets absorb most of the incident stellar radiation, advect this energy, then reradiate photons in preferential directions. Those photons carry away momentum, applying a force on the planet. Here we evaluate the resulting secular changes to the orbit, known as the Yarkovsky effect. For known transiting planets, typical fractional changes in semi-major axis are about 1% over their lifetime, but could be up to ~5% for close-in planets like OGLE-TR-56b or inflated planets like TrES-4. We discuss the origin of the correlation between semi-major axis and surface gravity of transiting planets in terms of various physical processes, finding that radiative thrusters are too weak by about a factor of 10 to establish the lower boundary that causes the correlation.