LHS 3154 b

LHS 3154 b is a Neptune-like exoplanet with a minimum mass of 13.2 {{Earth mass|link=y}} and an estimated radius of 3.65 {{Earth radius|link=y}}.{{cite arXiv |last1=Stefansson |first1=Gudmundur |title=An extreme test case for planet formation: a close-in Neptune orbiting an ultracool star |date=2023-03-01 |eprint=2303.13321 |last2=Mahadevan |first2=Suvrath |last3=Miguel |first3=Yamila |last4=Robertson |first4=Paul |last5=Delamer |first5=Megan |last6=Kanodia |first6=Shubham |last7=Cañas |first7=Caleb |last8=Winn |first8=Joshua |last9=Ninan |first9=Joe|class=astro-ph.EP }} It orbits its parent star at a distance of {{Convert|0.02262|AU|km}}, and completes one revolution every 3 days and 17 hours.{{Cite journal |last1=Stefánsson |first1=Guðmundur |last2=Mahadevan |first2=Suvrath |last3=Miguel |first3=Yamila |last4=Robertson |first4=Paul |last5=Delamer |first5=Megan |last6=Kanodia |first6=Shubham |last7=Cañas |first7=Caleb I. |last8=Winn |first8=Joshua N. |last9=Ninan |first9=Joe P. |last10=Terrien |first10=Ryan C. |last11=Holcomb |first11=Rae |last12=Ford |first12=Eric B. |last13=Zawadzki |first13=Brianna |last14=Bowler |first14=Brendan P. |last15=Bender |first15=Chad F. |date=December 2023 |title=A Neptune-mass exoplanet in close orbit around a very low-mass star challenges formation models |url=https://www.science.org/doi/10.1126/science.abo0233 |journal=Science |language=en |volume=382 |issue=6674 |pages=1031–1035 |doi=10.1126/science.abo0233 |pmid=38033084 |bibcode=2023Sci...382.1031S |s2cid=265506909 |issn=0036-8075|hdl=1887/3719388 |hdl-access=free }}{{Cite web |last=Martin |first=Pierre-Yves |date=1995 |title=Planet LHS 3154 b |url=https://exoplanet.eu/catalog/lhs_3154_b/ |access-date=2023-12-31 |website=exoplanet.eu |language=en}}

The discovery of LHS 3154 b raises doubts about the formation of planets, challenging current planetary models, because such a massive planet (13.2 {{Earth mass|link=y}}) was not expected to orbit such a small star, with just a ninth the mass of the Sun, and currently it is the only short-period Neptune-mass planet to orbit a low mass star. Although there are more massive exoplanets orbiting red dwarfs, such as TZ Arietis b and GJ 3512 b, they have wide orbits, with periods longer than 200 days, and likely formed in a different way than LHS 3154 b (core accretion), such as gravitational instability within a massive gaseous outer disk.

One of the ways in which planets form is through core accretion, where they form from initial cores that accrete dust and gas. Planets formed from core accretion orbiting low-mass stars should have a maximum mass of 5 {{Earth mass|link=y}}. LHS 3154 b, however, with a minimum mass of 13 {{Earth mass}}, presents a challenge to this theory.

Suvrath Mahadevan, one of the planet's discoverers, says: "The planet-forming disk around the low-mass star LHS 3154 is not expected to have enough solid mass to make this planet. But it’s out there, so now we need to reexamine our understanding of how planets and stars form.". According to Guðmundur Stefánsson, another discoverer of the planet, the recent discovery of LHS 3154 b creates doubts about the formation of planets around less massive stars, as it was previously believed that only terrestrial planets could form around these stars.{{Cite web |last=Dunham |first=Will |date=December 1, 2023 |title=Astronomers surprised to find planet too massive for its star |url=https://www.reuters.com/science/astronomers-surprised-find-planet-too-massive-for-its-star-2023-12-01/ |website=livescience.com}}

A team of scientists led by Suvrath Mahadevan discovered LHS 3154 b using the Habitable Zone Planet Finder, a spectrograph designed to detect planets orbiting cool stars that might have liquid surface water.{{Cite web |last=Gough |first=Evan |date=2023-12-05 |title=This Planet is Way Too Big for its Star |url=https://www.universetoday.com/164575/this-planet-is-way-too-big-for-its-star/ |access-date=2023-12-31 |website=Universe Today |language=en-US}} The discovery was announced on November 30, 2023, in the journal Science.

LHS 3154 is a dim red dwarf located at a distance of {{Convert|15.75|pc|ly}} from the Earth in the constellation Hercules.{{Efn|Constellation obtained with a right ascension of {{RA|16|06|33.79}} and a declination of {{DEC|+40|54|22.0}}{{Cite web |title=LP 224-38 |url=https://simbad.cds.unistra.fr/mobile/object.html?object_name=LP%20224-38 |access-date=December 31, 2023 |website=SIMBAD}} on this [https://djm.cc/constellation.html website].|name=Constellation|group=note}} With an apparent magnitude of 17.5, it cannot be seen with the naked eye or even a small telescope.{{Cite web |title=★ LP 224-38 |url=https://www.stellarcatalog.com/stars/lp-224-38 |access-date=2023-12-31 |website=Stellar Catalog |language=en}} LHS 3154 has a radius of 0.14 {{Solar radius|link=y}} and a mass of 0.11 {{Solar mass|link=Y}}, which is comparable to the nearby red dwarf Wolf 359.

Category:Exoplanets discovered in 2023

Category:Exoplanets detected by radial velocity