Low-albedo Surfaces of Lava Worlds
Abstract
Hot super-Earths are exoplanets with short orbital periods (<10 days), heated by their host stars to temperatures high enough for their rocky surfaces to become molten. A few hot super-Earths exhibit high geometric albedos (>0.4) in the Kepler band (420-900 nm). We are motivated to determine whether reflection from molten lava and quenched glasses (a product of rapidly cooled lava) on the surfaces of hot super-Earths contribute to the observationally inferred high geometric albedos. We experimentally measure reflection from rough- and smooth-textured quenched glasses of both basalt and feldspar melts. For lava reflectance values, we use specular reflectance values of molten silicates from non-crystalline solids literature. Integrating the empirical glass reflectance function and non-crystalline solids reflectance values over the dayside surface of the exoplanet at secondary eclipse yields an upper limit for the albedo of a lava-quenched glass planet surface of ∼0.1. We conclude that lava planets with solid (quenched glass) or liquid (lava) surfaces have low albedos. The high albedos of some hot super-Earths are most likely explained by atmospheres with reflective clouds (or, for a narrow range of parameter space, possibly Ca/Al oxide melt surfaces). Lava planet candidates in TESS data can be identified for follow-up observations and future characterization.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2020
- DOI:
- 10.3847/1538-4357/ab9cba
- arXiv:
- arXiv:2008.02789
- Bibcode:
- 2020ApJ...898..160E
- Keywords:
-
- Exoplanet surface characteristics;
- Experimental techniques;
- Super Earths;
- Exoplanet atmospheres;
- Exoplanet surface composition;
- Interdisciplinary astronomy;
- 496;
- 2078;
- 1655;
- 487;
- 2022;
- 804;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 18 pages, 14 figures, 4 tables, published in ApJ