Exploring Super-Earth Surfaces: Albedo of Near-Airless Magma Ocean Planets and Topography

TL;DR

This study develops an analytical model to estimate the spherical albedo of airless magma ocean planets, considering surface roughness and composition, and applies it to Kepler-10b to infer possible surface characteristics.

Contribution

It introduces a new analytic function for albedo based on surface roughness and composition, validated through simulations and applied to observational data.

Findings

Albedo varies with surface roughness, composition, and wavelength.

Kepler-10b's high albedo suggests a metallic oxide-rich surface.

Model can help interpret observational albedo data for exoplanets.

Abstract

In this paper we propose an analytic function for the spherical albedo values of airless and near-airless magma ocean planets (AMOPs). We generated 2-D fractal surfaces with varying compositions onto which we individually threw 10,000 light rays. Using an approximate form of the Fresnel equations we measured how much of the incident light was reflected. Having repeated this algorithm on varying surface roughnesses we find the spherical albedo as a function of the Hurst exponent, the geochemical composition of the magma, and the wavelength. As a proof of concept, we used our model on Kepler-10b to demonstrate the applicability of our approach. We present the spherical albedo values produced from different lava compositions and multiple tests that can be applied to observational data in order to determine their characteristics. Currently, there is a strong degeneracy in the surface composition of AMOPs due to the large uncertainties in their measured spherical albedos. In spite of this, when applied to Kepler-10b we show that its high albedo could be caused by a moderately wavy ocean that is rich in oxidised metallic species such as FeO, $\rm Fe_{2}O_{3}$, $\rm Fe_{3}O_{4}$. This would imply that Kepler-10b is a coreless or near-coreless body.