Exoplanetology: Exoplanets & Exomoons

Detection Of An Earth-sized Exoplanet Orbiting The Nearby Ultracool Dwarf Star SPECULOOS-3

By Keith Cowing
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astro-ph.EP
June 4, 2024
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Detection Of An Earth-sized Exoplanet Orbiting The Nearby Ultracool Dwarf Star SPECULOOS-3
Comparison of SPECULOOS-3 b with other rocky exoplanets. a) Sizes of host stars and incident stellar flux of known sub-Neptune-sized exoplanets. The size of the symbols scales linearly with the radius of the planet. The background is colour-coded according to stellar size (in units of the Sun’s size), with the ultra-cool dwarf regime shown in orange. The positions of the Solar System terrestrial planets are shown for reference. One can see on this Figure that SPECULOOS-3 b extends the unique planet sample of TRAPPIST-1 to a larger stellar flux. b) SPECULOOS-3 b in the context of other known transiting terrestrial exoplanets (Rp < 1.6R⊕) that are cool enough (Teq < 880 K [80]) to have a dayside made of solid rock (in contrast to hotter magma worlds with molten surfaces). The planets are shown as a function of their radius and their Emission Spectroscopy Metric [62]. They are color-coded as a function of their equilibrium temperature. The shaded green area highlights planetary radii most similar to Earth’s (0.9–1.1 R⊕). The dashed horizontal line represents the threshold of ESM=7.5 recommended by ref. [62] to identify the top targets for emission spectroscopy with JWST. SPECULOOS-3 b is one of the smallest planets amenable to emission spectroscopy with MIRI/LRS. Data from https://exoplanetarchive.ipac.caltech.edu (16th of October 2023). — astro-ph.EP

Located at the bottom of the main sequence, ultracool dwarf stars are widespread in the solar neighbourhood. Nevertheless, their extremely low luminosity has left their planetary population largely unexplored, and only one of them, TRAPPIST-1, has so far been found to host a transiting planetary system.

In this context, we present the SPECULOOS project’s detection of an Earth-sized planet in a 17 h orbit around an ultracool dwarf of M6.5 spectral type located 16.8 pc away. The planet’s high irradiation (16 times that of Earth) combined with the infrared luminosity and Jupiter-like size of its host star make it one of the most promising rocky exoplanet targets for detailed emission spectroscopy characterization with JWST.

Indeed, our sensitivity study shows that just ten secondary eclipse observations with the Mid-InfraRed Instrument/Low-Resolution Spectrometer on board JWST should provide strong constraints on its atmospheric composition and/or surface mineralogy.

Discovery transit photometry of SPECULOOS-3 b. Transit photometry obtained by SAINT-EX and SNO-Artemis between 2021 and 2023 (phase-folded, detrended and binned per 2 minutes). The light curves are shifted along the y-axis for clarity. The SAINT-EX, SNO I + z, i ′ , and z ′ measurements are, on average, the means of 2.8, 21.6, 6.0, and 2.5 photometric data points. The error bars are the mean errors of the points within the bin divided by the square root of the number of points. The black lines show the best-fit transit models. — astro-ph.EP

Michaël Gillon, Peter P. Pedersen, Benjamin V. Rackham, Georgina Dransfield, Elsa Ducrot, Khalid Barkaoui, Artem Y. Burdanov, Urs Schroffenegger, Yilen Gómez Maqueo Chew, Susan M. Lederer, Roi Alonso, Adam J. Burgasser, Steve B. Howell, Norio Narita, Julien de Wit, Brice-Olivier Demory, Didier Queloz, Amaury H. M. J. Triaud, Laetitia Delrez, Emmanuël Jehin, Matthew J. Hooton, Lionel J. Garcia, Clàudia Jano Muñoz, Catriona A. Murray, Francisco J. Pozuelos, Daniel Sebastian, Mathilde Timmermans, Samantha J. Thompson, Sebastián Zúñiga-Fernández 1, Jesús Aceituno, Christian Aganze, Pedro J. Amado, Thomas Baycroft, Zouhair Benkhaldoun, David Berardo, Emeline Bolmont, Catherine A. Clark, Yasmin T. Davis, Fatemeh Davoudi, Zoë L. de Beurs, Jerome P. de Leon, Masahiro Ikoma, Kai Ikuta, Keisuke Isogai, Izuru Fukuda, Akihiko Fukui, Roman Gerasimov, Mourad Ghachoui, Maximilian N. Günther, Samantha Hasler, Yuya Hayashi, Kevin Heng, Renyu Hu, Taiki Kagetani, Yugo Kawai, Kiyoe Kawauchi, Daniel Kitzmann, Daniel D. B. Koll, Monika Lendl, John H. Livingston, Xintong Lyu, Erik A. Meier Valdés, Mayuko Mori, James J. McCormac, Felipe Murgas, Prajwal Niraula, Enric Pallé, Ilse Plauchu-Frayn, Rafael Rebolo, Laurence Sabin, Yannick Schackey, Nicole Schanche, Franck Selsis, Alfredo Sota, Manu Stalport, Matthew R. Standing, Keivan G. Stassun, Motohide Tamura, Christopher A. Theissen, Martin Turbet, Valérie Van Grootel, Roberto Varas, Noriharu Watanabe, Francis Zong Lang

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2406.00794 [astro-ph.EP] (or arXiv:2406.00794v1 [astro-ph.EP] for this version)
Related DOI:
https://doi.org/10.1038/s41550-024-02271-2
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Submission history
From: Michael Gillon
[v1] Sun, 2 Jun 2024 16:32:37 UTC (2,236 KB)
https://arxiv.org/abs/2406.00794
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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