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Updated: Apr 27, 2026

Surface Mapping of Earth-like Exoplanets using Single Point Light Curves
Published on: May 10, 2020
Exoplanet detection. Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581
Paul Robertson1, Suvrath Mahadevan2, Michael Endl3
1Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA. Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802, USA. pmr19@psu.edu.
Abstract:
The M dwarf star Gliese 581 is believed to host four planets, including one (GJ 581d) near the habitable zone that could possibly support liquid water on its surface if it is a rocky planet. The detection of another habitable-zone planet--GJ 581g--is disputed, as its significance depends on the eccentricity assumed for d. Analyzing stellar activity using the Hα line, we measure a stellar rotation period of 130 ± 2 days and a correlation for Hα modulation with radial velocity. Correcting for activity greatly diminishes the signal of GJ 581d (to 1.5 standard deviations) while significantly boosting the signals of the other known super-Earth planets. GJ 581d does not exist, but is an artifact of stellar activity which, when incompletely corrected, causes the false detection of planet g.
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