Exoplanets & Exomoons

Separated Twins Or Just Siblings? A Multi-planet System Around An M Dwarf Including A Cool sub-Neptune

By Keith Cowing
Status Report
October 24, 2023
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Separated Twins Or Just Siblings? A Multi-planet System Around An M Dwarf Including A Cool sub-Neptune
TESS observations of TOI-904. Panel (a): Raw observations of each TESS sector, with 2-minute data shown in light grey and 10-minute binned data shown in dark grey. We show the Tukey biweight trend calculated with the wotan (Hippke et al. 2019) library of the variability is shown in dark blue. Each planet transit is denoted by an arrow at the bottom of the graph, with blue denoting transits of TOI-904 b and gold denoting transits TOI-904 c. Panel (b): TESS data detrended by the same fit, with each transit high-lighted in the same color as the arrows in the previous figure. Panel (c): The phase folded light curves of transits of TOI-904 b with the transit fit including a shaded region denoting 1σ uncertainty. Panel (d): The phase-folded light curves of TOI-904 c with the transit fit including a shaded region denoting 1σ uncertainty. — astro-ph.EP

We report the discovery of two TESS sub-Neptunes orbiting the early M dwarf TOI-904 (TIC 261257684). Both exoplanets, TOI-904 b and c, were initially observed in TESS sector 12 with twin sizes of 2.49R⊕ and 2.31R⊕, respectively.

Through observations in five additional sectors in the TESS primary mission and the first and second extended missions, the orbital periods of both planets were measured to be 10.887±0.001 and 83.999±0.001 days, respectively. Reconnaissance radial velocity measurements (taken with EULER/CORALIE) and high resolution speckle imaging with adaptive optics (obtained from SOAR/HRCAM and Gemini South/ZORRO) show no evidence of an eclipsing binary or a nearby companion, which together with the low false positive probabilities calculated with the statistical validation software TRICERATOPS establish the planetary nature of these candidates.

The outer planet, TOI-904 c, is the longest-period M dwarf exoplanet found by TESS, with an estimated equilibrium temperature of 217K. As the three other validated planets with comparable host stars and orbital periods were observed by Kepler around much dimmer stars (Jmag > 12), TOI-904 c, orbiting a brighter star (Jmag = 9.6), is the coldest M dwarf planet easily accessible for atmospheric follow-up.

Future mass measurements and transmission spectroscopy of the similar sized planets in this system could determine whether they are also similar in density and composition, suggesting a common formation pathway, or whether they have distinct origins.

Plots of all known transiting multi-planet systems (Left) and cold planets (Right; Teq <300 K) around M dwarf stars. Each system is shown as a function of system name (left y-axis), stellar mass (right y-axis), semi-major axis (x-axis) planet equilibrium temperature (color) and planet radius (point size). TOI-904 is shown at the bottom of each panel with a gold horizontal line. — astro-ph.EP

Mallory Harris, Diana Dragomir, Ismael Mireles, Karen A. Collins, Solène Ulmer-Moll, Steve B. Howell, Keivan G. Stassun, George Zhou, Carl Ziegler, François Bouchy, César Briceño, David Charbonneau, Kevin I. Collins, Gábor Fűűrész, Natalia M. Guerrero, Jon M. Jenkins, Eric L. N. Jensen, Martti H. K. Kristiansen, Nicholas Law, Monika Lendl, Andrew W. Mann, Hugh P. Osborn, Samuel N. Quinn, George R. Ricker, Richard P. Schwarz, Sara Seager, Eric B. Ting, Roland Vanderspek, David Watanabe, Joshua N. Winn

Comments: 18 pages, 6 figures, Accepted by the Astrophysical Journal Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2310.15118 [astro-ph.EP] (or arXiv:2310.15118v1 [astro-ph.EP] for this version)
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Submission history
From: Mallory Harris
[v1] Mon, 23 Oct 2023 17:24:10 UTC (3,708 KB)

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) 🖖🏻