Rotation Period Detection for Earth-like Exoplanets

Creators: Li, Jiazheng¹; Jiang, Jonathan H.²; Yang, Huanzhou³; Abbot, Dorian S.³; Hu, Renyu²; Komacek, Thaddeus D.³; Bartlett, Stuart J.¹; Yung, Yuk L.^{1, 2}

1. California Institute of Technology
2. Jet Propulsion Lab
3. University of Chicago

Abstract

A terrestrial planet's rotation period is one of the key parameters that determines its climate and habitability. Current methods for detecting the rotation period of exoplanets are not suitable for terrestrial exoplanets. Here we demonstrate that, under certain conditions, the rotation period of an Earth-like exoplanet will be detectable using direct-imaging techniques. We use a global climate model that includes clouds to simulate reflected starlight from an Earth-like exoplanet and explore how different parameters (e.g., orbital geometry, wavelength, time resolution) influence the detectability of the planet's rotation period. We show that the rotation period of an Earth-like exoplanet is detectable using visible-wavelength channels with time-series monitoring at a signal-to-noise ratio (S/N) >20 with ∼5–15 rotation periods of data, while the rotation period of a planet with full ocean coverage is unlikely to be detectable. To better detect the rotation period, one needs to plan the observation so that each individual integration would yield a S/N >10, while keeping the integration time shorter than 1/6 to 1/4 of the rotation period of the planet. Our results provide important guidance for rotation period detection of Earth-like exoplanets in reflected light using future space telescopes.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We thank Eric Wolf for developing, maintaining, and making publicly available ExoCAM. This work is supported by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. We acknowledge the funding support from the NASA Exoplanet Research Program NNH18ZDA001N-2XRP. This work is also supported by the NASA Astrobiology Program grant No. 80NSSC18K0829 and benefited from participation in the NASA Nexus for Exoplanet Systems Science research coordination network. This work was completed with resources provided by the University of Chicago Research Computing Center. T.D.K. acknowledges support from the 51 Pegasi b fellowship in Planetary Astronomy sponsored by the Heising-Simons Foundation. Y.L.Y. was supported in part by an NAI Virtual Planetary Laboratory grant from the University of Washington (YLY.001377-1-JPL.1616476).

Data Availability

The ExoCAM model source code and related data are available to download from https://github.com/storyofthewolf/ExoCAM. The computed data underlying this article are described in the article. For additional questions regarding the data and code sharing, please contact the corresponding author.

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