Exploring super-Earth surfaces: Albedo of near-airless magma ocean planets and topography

• Published in: Icarus (New York, N.Y. 1962) Vol. 358; p. 114175
• Main Authors: Modirrousta-Galian, Darius, Ito, Yuichi, Micela, Giuseppina
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.04.2021
• Subjects: Extra-solar planets; Interiors; Spectrophotometry; Terrestrial planets; Volcanism; Terrestrial planets; Interiors; Extra-solar planets; Spectrophotometry; Volcanism
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2020.114175

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, Fe2O3, Fe3O4. This would imply that Kepler-10b is a coreless or near-coreless body. •2-D ray tracing simulations on fractal magma ocean surfaces are used.•An analytic approximation is found for the spherical albedo of molten super-Earths.•Various materials and their properties are listed for easy usage within our model.•The high bolometric Bond albedo of Kepler-10b may be due to an Fe-rich magma ocean.•Our model can be implemented into general circulation and radiative transfer models.