Proxima Centauri b is not a transiting exoplanet

Jenkins, James S.; Harrington, Joseph; Challener, Ryan C.; Kurtovic, Nicolás T.; Ramirez, Ricardo; Peña, Jose; McIntyre, Kathleen J.; Himes, Michael D.; Rodríguez, Eloy; Anglada-Escudé, Guillem; Dreizler, Stefan; Ofir, Aviv; Peña Rojas, Pablo A.; Ribas, Ignasi; Rojo, Patricio; Kipping, David; Butler, R. Paul; Amado, Pedro J.; Rodríguez-López, Cristina; Kempton, Eliza M.-R.; Palle, E.; Murgas, F.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 487, Issue 1, p.268-274

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7
2019
Number of authors
22
IAC number of authors
2
Citations
22
Refereed citations
19
Description
We report Spitzer Space Telescope observations during predicted transits of the exoplanet Proxima Centauri b. As the nearest terrestrial habitable-zone planet we will ever discover, any potential transit of Proxima b would place strong constraints on its radius, bulk density, and atmosphere. Subsequent transmission spectroscopy and secondary-eclipse measurements could then probe the atmospheric chemistry, physical processes, and orbit, including a search for biosignatures. However, our photometric results rule out planetary transits at the 200 ppm level at 4.5 μm, yielding a 3σ upper radius limit of 0.4 R⊕ (Earth radii). Previous claims of possible transits from optical ground- and space-based photometry were likely correlated noise in the data from Proxima Centauri's frequent flaring. Our study indicates dramatically reduced stellar activity at near-to-mid infrared wavelengths, compared to the optical. Proxima b is an ideal target for space-based infrared telescopes, if their instruments can be configured to handle Proxima's brightness.
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