Finding Mountains with Molehills: The Detectability of Exotopography

TL;DR

This paper explores the potential for detecting exoplanet topography through transit light curve analysis, proposing a method to identify surface features like mountains and craters using photometric scatter.

Contribution

It introduces a novel approach to quantify exoplanet surface relief by analyzing transit light curve variations caused by planetary rotation and topography.

Findings

Detection of topography is feasible with upcoming telescopes like Colossus or OWL.

Approximately 400 transits could reveal surface features for nearby rocky exoplanets.

The method requires about 20 hours of observation time for ideal cases.

Abstract

Mountain ranges, volcanoes, trenches, and craters are common on rocky bodies throughout the Solar System, and we might we expect the same for rocky exoplanets. With ever larger telescopes under design and a growing need to not just detect planets but also to characterize them, it is timely to consider whether there is any prospect of remotely detecting exoplanet topography in the coming decades. To test this, we devised a novel yet simple approach to detect and quantify topographical features on the surfaces of exoplanets using transit light curves. If a planet rotates as it transits its parent star, its changing silhouette yields a time-varying transit depth, which can be observed as an apparent and anomalous increase in the photometric scatter. Using elevation data for several rocky bodies in our solar system, we quantify each world's surface integrated relief with a "bumpiness" factor, and calculate the corresponding photometric scatter expected during a transit. Here we describe the kinds of observations that would be necessary to detect topography in the ideal case of Mars transiting a nearby white dwarf star. If such systems have a conservative occurrence rate of 10%, we estimate that the upcoming Colossus or OWL telescopes would be able to detect topography with <20 hours of observing time, which corresponds to ~400 transits with a duration of 2 minutes and orbital period of ~10 hours.