Can Rocky Exoplanets with Rings Pose as Sub-Neptunes?

Abstract

In our solar system, the presence of rings is exclusive to the gas giants, but is this the case for all planetary systems? In principle, it seems that rocky exoplanets could also have rings, which could be searched for by studying their subtle imprint on the ingress and egress of transits. Unfortunately, such effects are difficult to measure and require high precision photometric and/or spectroscopic observations. At the most basic level though, the presence of rings would result in an increased transit depth that could be mistaken as an anonymously large radius. Motivated by this, I consider how a population of exoplanets with rings would impact radius measurements, focusing on Earth-like exoplanets. It is found that this population introduces an enhancement of inferred radii in the range of $\sim 2-3R_{\oplus }$, not unlike the sub-Neptunes that have been identified in recent transit surveys. Whether rings can explain all or most sub-Neptunes seems difficult, since it would require a large fraction of rocky planets to have rings ($\gtrsim 40\%$) and/or a factor of $\sim 2-3$ increase in the number of planets with radii $\lesssim 1.2R_{\oplus }$. Even if rings cannot explain all sub-Neptunes, this work suggests that focusing on those planets currently classified as sub-Neptunes may be a good starting place for finding rocky planets with rings.

9 pages, 7 figures, fixed obliquity distribution for version accepted for publication in AJ

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• A Framework for Characterizing Transmission Spectra of Exoplanets with Circumplanetary Rings
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