Exoplanetology: Exoplanets & Exomoons

GJ 238 b: A 0.57 Earth Radius Planet Orbiting an M2.5 Dwarf Star at 15.2 pc

By Keith Cowing
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astro-ph.EP
July 26, 2024
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GJ 238 b: A 0.57 Earth Radius Planet Orbiting an M2.5 Dwarf Star at 15.2 pc
Stellar insolation at a planet’s orbit as a function of escape velocity from the planet’s surface, in log-log scale. Based on data from the NASA Exoplanet Archive downloaded on May 18, 2023. The empirical “cosmic shoreline” and the water vapor greenhouse runaway threshold (Zahnle & Catling 2017) are shown in cyan and yellow, respectively. Planets are categorized into terrestrial planets (magenta), sub-Neptunes (blue), Neptune-like planets (green), and gas giants (yellow) based on radius, see legend. The red line shows the possible range of escape velocities of GJ 238 b. Because only radius, but not mass, is known, the two endpoints represent two extreme interior scenarios – a 100% iron composition and a 100% silicate composition. — astro-ph.EP

We report the discovery of the transiting planet GJ 238 b, with a radius of 0.566±0.014 R⊕ (1.064±0.026 times the radius of Mars) and an orbital period of 1.74 day.

The transit signal was detected by the TESS mission and designated TOI-486.01. The star’s position close to the Southern ecliptic pole allows for almost continuous observations by TESS when it is observing the Southern sky.

The host star is an M2.5 dwarf with V=11.57±0.02 mag, K=7.030±0.023 mag, a distance of 15.2156±0.0030 pc, a mass of 0.4193+0.0095−0.0098 M⊙, a radius of 0.4314+0.0075−0.0071 R⊙, and an effective temperature of 3,485±140 K.

We validate the planet candidate by ruling out or rendering highly unlikely each of the false positive scenarios, based on archival data and ground-based follow-up observations. Validation was facilitated by the host star’s small size and high proper motion, of 892.633±0.025 mas yr−1.

Speckle imaging of GJ 238. Each panel shows the contrast curve, in magnitude difference as a function of angular distance from the target in arcsec, and the speckle auto-correlation function (ACF) in the inset. Top: Speckle imaging obtained at SOAR in the I band, on UT 2020 February 10. Bottom: Speckle imaging obtained with GeminiSouth/Zorro, on UT 2020 March 13, in 562 nm (blue line) and 832 nm (red line and inset). — astro-ph.EP

Evan Tey, Avi Shporer, Zifan Lin, Keivan G. Stassun, Jack J. Lissauer, Coel Hellier, Karen A. Collins, Kevin I. Collins, Geof Wingham, Howard M. Relles, Franco Mallia, Giovanni Isopi, John F. Kielkopf, Dennis M. Conti, Richard P. Schwarz, Aldo Zapparata, Steven Giacalone, Elise Furlan, Zachary D. Hartman, Steve B. Howell, Nicholas J. Scott, Carl Ziegler, Cesar Briceno, Nicholas Law, Andrew W. Mann, David Charbonneau, Zahra Essack, Stephanie Striegel, George R. Ricker, Roland Vanderspek, Sara Seager, Joshua N. Winn, Jon M. Jenkins

Comments: Published in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2407.18199 [astro-ph.EP] (or arXiv:2407.18199v1 [astro-ph.EP] for this version)
Journal reference: AJ, 167, 283 (2024)
Related DOI:
https://doi.org/10.3847/1538-3881/ad3df1
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Submission history
From: Avi Shporer
[v1] Thu, 25 Jul 2024 17:08:41 UTC (2,386 KB)
https://arxiv.org/abs/2407.18199

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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