Astronomy:L 98-59 b

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L 98-59 b
Artist's impression and size comparison with Earth and Mars
Discovery[1]
Discovery dateMarch 2019
Transit
Orbital characteristics[3]
0.02191+0.00080
−0.00084 astronomical unit|AU
Eccentricity0.103+0.117
−0.045
Orbital period2.2531136+0.0000012
−0.0000015 d
Inclination87.71°+1.16°
−0.44°
Semi-amplitude0.56±0.16 m/s[2]
StarL 98-59
Physical characteristics[3]
Mean radius0.850+0.061
−0.047 R🜨
Mass0.47+0.13
−0.15 M🜨[2]
Mean density4.3+1.2
−1.9 g/cm3[2]
Physics627+33
−36 K (354 °C; 669 °F, equilibrium)


L 98-59 b is an exoplanet having a size between that of the Earth and Mars and a mass only half that of Venus.[3] It orbits L 98-59, a red dwarf star 34.6 light-years away in the constellation Volans. There are at least 4 (possibly 5) other planets in the system: L 98-59 c, d, e, f and the unconfirmed ".06".[3][4] Its discovery was announced on 27 June 2019 in The Astronomical Journal[1] and in a NASA press release. It was the smallest planet discovered by TESS[5] until the discovery of LHS 1678 b,[6] and was the lowest-mass planet whose mass had been measured using radial velocities[3] until Proxima Centauri d was found in 2022.[7]

Characteristics

L 98-59 b orbits its star in 2.25 days and stays so close to the star that it receives 22 times more energy than Earth receives from the Sun. There are 4 confirmed planets in the system but they are not in the habitable zone of the host star.[5] The temperature of the planet detected by TESS is 330 °C.[8] In 2022, transmission spectroscopy indicated that the planet has either no atmosphere or an opaque atmosphere with high-altitude hazes.[9]

Transmission spectroscopy observations with the James Webb Space Telescope NIRSpec published in 2025 favor the presence of a sulfur dioxide atmosphere. This is likely driven by volcanism, implying that L 98-59 b experiences at least eight times as much volcanism and tidal heating as Io.[10]

References

  1. ↑ 1.0 1.1 Kostov, Veselin B. et al. (July 2019). "The L 98-59 System: Three Transiting, Terrestrial-size Planets Orbiting a Nearby M Dwarf". The Astronomical Journal 158 (1): 32. doi:10.3847/1538-3881/ab2459. Bibcode: 2019AJ....158...32K. 
  2. ↑ 2.0 2.1 2.2 Rajpaul, Vinesh M.; Barragán, Oscar; Zicher, Norbert (June 2024). "A non-zero Doppler amplitude is not enough: revisiting the putative radial velocity detection of sub-Venus exoplanet L 98-59b". Monthly Notices of the Royal Astronomical Society 530 (4): 4665–4675. doi:10.1093/mnras/stae778. Bibcode: 2024MNRAS.530.4665R. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Demangeon, Oliver D. S.Expression error: Unrecognized word "etal". (July 2021). "A warm terrestrial planet with half the mass of Venus transiting a nearby star". Astronomy & Astrophysics 653: 38. doi:10.1051/0004-6361/202140728. Bibcode: 2021A&A...653A..41D. https://www.eso.org/public/archives/releases/sciencepapers/eso2112/eso2112a.pdf. 
  4. ↑ Schwarz, Paul; Dreizler, Stefan; Heller, René (2025-07-08). "Confirmation of a non-transiting planet in the habitable zone of the nearby M dwarf L 98-59". arXiv:2507.06413 [astro-ph.EP].
  5. ↑ 5.0 5.1 Garner, Rob (2019-06-24). "NASA's TESS Mission Finds Its Smallest Planet Yet" (in en). http://www.nasa.gov/feature/goddard/2019/nasa-s-tess-mission-finds-its-smallest-planet-yet. 
  6. ↑ Silverstein, Michele L.; Schlieder, Joshua E.; Barclay, Thomas; Hord, Benjamin J.; Jao, Wei-Chun; Vrijmoet, Eliot Halley; Henry, Todd J.; Cloutier, Ryan et al. (2022-04-01). "The LHS 1678 System: Two Earth-Sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc". The Astronomical Journal 163 (4): 151. doi:10.3847/1538-3881/ac32e3. ISSN 0004-6256. Bibcode: 2022AJ....163..151S. 
  7. ↑ Faria, J. P.; Suárez Mascareño, A. et al. (January 4, 2022). "A candidate short-period sub-Earth orbiting Proxima Centauri". Astronomy & Astrophysics (European Southern Observatory) 658: 17. doi:10.1051/0004-6361/202142337. Bibcode: 2022A&A...658A.115F. https://www.eso.org/public/archives/releases/sciencepapers/eso2202/eso2202a.pdf. 
  8. ↑ "Canicule ? Il fait 330 degrés sur la petite exoplanète découverte par le télescope spatial TESS" (in fr). 2019-07-01. https://www.numerama.com/sciences/530111-canicule-il-fait-330-degres-sur-la-petite-exoplanete-decouverte-par-le-telescope-spatial-tess.html. 
  9. ↑ Damiano, Mario; Hu, Renyu; Barclay, Thomas; Zieba, Sebastian; Kreidberg, Laura; Brande, Jonathan; Colon, Knicole D.; Covone, Giovanni et al. (2022), "A Transmission Spectrum of the Sub-Earth Planet L98-59 b in 1.1–1.7 μm", The Astronomical Journal 164 (5): 225, doi:10.3847/1538-3881/ac9472, Bibcode: 2022AJ....164..225D 
  10. ↑ Bello-Arufe, Aaron et al. (January 2025). "Evidence for a volcanic atmosphere on the sub-Earth L98-59b". The Astrophysical Journal Letters. 



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