The single beacon: progresses in understanding Earth as an exoplanet using DSCOVR/EPIC observations
Abstract
Almost 6000 exoplanets have thus far been confirmed, revolutionizing our understanding of planetary habitability. Yet, despite the identification of Earth-like exoplanets, definitive evidence of extraterrestrial life remains elusive. Studying Earth, the only confirmed habitable and inhabited planet, as a proxy exoplanet provides critical insights for interpreting forthcoming exoplanet direct-imaging data. Observations from the Deep Space Climate Observatory/Earth Polychromatic Imaging Camera (DSCOVR/EPIC), located at the first Sun-Earth Lagrangian point (L1), offer a unique opportunity to analyze Earth's full-disk, single-point multi-spectrum light curves. Here, we review progress that treat EPIC data as if Earth were an unresolved, distant world. These studies reveal information about planetary rotation, cloud patterns, and surface types. Autocorrelation of the time series recovers the 24 h rotation period, while principal component analysis (PCA) highlights the land-ocean spectral contrast, enabling the reconstruction of a coarse two-dimensional surface map. Modeling studies further quantify the contributions of different planetary surfaces and clouds to Earth's observable brightness, with low-level clouds playing a dominant role. Additionally, the effects of Earth's atmosphere, particularly within strong oxygen bands, have been simulated and evaluated. The rich temporal–spectral "light-curve complexity" produced by its heterogeneous surface and dynamic atmosphere has emerged as a practical, observation-based metric of habitability. Comparisons with simulations and other solar system planets demonstrate that Earth's light curves exhibit the highest complexity, underscoring its unique status as the only known habitable and inhabited exoplanet. These findings provide a valuable observational baseline for future exoplanet studies, refining our ability to recognize life-supporting worlds beyond the Solar System.
Copyright and License
© 2025 Jian, Gu, Fan, Bartlett, Yang, Jiang, Luo and Yung. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Funding
The author(s) declare that financial support was received for the research and/or publication of this article. SF acknowledges funding from the Stable Support Plan Program for the Higher Education Institutions of the Shenzhen Science and Technology Innovation Commission through grant No. 20231115103030002. JHJ acknowledged the support from the Jet Propulsion Laboratory, California Institute of Technology, sponsored by NASA. JHJ and SJB acknowledge support from the NASA XRP (Exoplanets Research Program) grant no. 22-XRP22_2-0044.
Contributions
XJ: Writing – review and editing, Writing – original draft. LG: Writing – review and editing, Methodology. SF: Project administration, Writing – review and editing, Methodology. SJB: Methodology, Writing – review and editing. JY: Writing – review and editing. JHJ: Writing – review and editing, Conceptualization. YL: Validation, Writing – review and editing. YY: Supervision, Writing – review and editing.
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Additional details
- Shenzhen Municipal Science and Technology Innovation Council
- 20231115103030002
- Jet Propulsion Laboratory
- National Aeronautics and Space Administration
- 22-XRP22_2-0044
- Accepted
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2025-07-19
- Caltech groups
- Division of Geological and Planetary Sciences (GPS)
- Publication Status
- Published