# TOI-421 > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/TOI-421 > Markdown URL: https://mediated.wiki/source/TOI-421.md > Source: https://en.wikipedia.org/wiki/TOI-421 > Source revision: 1356800608 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Planetary system in the constellation Lepus}} {{starbox begin}} {{starbox observe | epoch = J2000 | constell = [Lepus](/source/Lepus_(constellation)) | ra = {{RA|05|27|24.8259}} | dec = {{DEC|-14|16|37.046}} | appmag_v = 9.93 }} {{starbox character | type = [Main sequence](/source/Main_sequence) | class = G9V }} {{starbox astrometry | radial_v = {{val|79.41|0.16}} | prop_mo_ra = {{val|-35.743|(11)}} | prop_mo_dec = {{val|50.387|(11)}} | pm_footnote = | parallax = 13.3337 | p_error = 0.0117 | parallax_footnote = }} {{starbox detail | source = | mass = {{val|0.833|0.048|0.054}} | radius = {{val|0.866|0.006}} | gravity = {{val|4.48|0.03}} | temperature = {{val|5291|64}} | metal_fe = {{val|-0.044|0.04}} | rotation = {{val|39.6|1.6|ul=d}} | rotational_velocity = {{val|1.8|1.0}} | age_gyr = {{val|10.9|2.9|5.2}} }} {{starbox catalog | names = {{odlist |BD=-14 1137 |GSC=05344-01206 |2MASS=J05272482-1416370 |PPM=711571 |TIC=94986319 |TOI=421 |TYC=5344-1206-1 |Gaia DR2=2984582227215748864 |Gaia DR3=2984582227215748864}} }} {{starbox reference | Simbad = BD-14+1137 | NSTED = TOI-421 }} {{starbox end}} '''TOI-421''' (also known as '''BD−14 1137''') is a [G-type main-sequence star](/source/G-type_main-sequence_star) located in the constellation [Lepus](/source/Lepus_(constellation)). The star hosts two [transiting exoplanet](/source/transiting_exoplanet)s discovered in 2020 and forms a [visual binary](/source/visual_binary) system with a nearby [red dwarf](/source/red_dwarf) star '''BD−14 1137 B'''. Both planets are [hot Neptune](/source/hot_Neptune)s well-suited for atmospheric characterization. Due to the star's old age, knowing the composition of their atmosphere can provide valuable insights for validation of atmospheric evolution models. == Stellar characteristics == TOI-421 is a [Solar-type](/source/Solar_analog) star, of similar [metallicity](/source/metallicity) though somewhat smaller the [Sun](/source/Sun). According to the [evolutionary models](/source/Stellar_evolution), it is thought to be an old star, age of approximately 10 billion years. Observations of variability related to its ~42-day [rotation](/source/stellar_rotation) indicate a low level of [stellar activity](/source/stellar_activity) with only few surface [spots](/source/starspot), dominated by [plages](/source/solar_plage). The red dwarf companion is positioned {{val|29.4|u=arcsec}} NW, corresponding to actual separation of approximately {{val|2200|ul=AU}}. == Planetary system == A discovery of two planets [transiting](/source/Astronomical_transit) the star was announced in 2020, based on [TESS](/source/TESS) observations between {{date|2018-11-15}} and {{date|2019-01-07}}, and confirmed with ground-based observations. The TESS light curve features two series of transit signals identified with the two planets; a deeper one every ~16.1 days and a shallower one every ~5.2 days. The orbital parameters were refined in a 2024 study that included additional transit observations by TESS and [CHEOPS](/source/CHEOPS) as well as [radial velocity](/source/Doppler_spectroscopy) measurements for determination of mass of the planets, showing that both planets have moderately eccentric orbits. The study did not find evidence of [transit-timing variation](/source/transit-timing_variation)s, which could hint at existence of additional non-transiting planets. {{Orbitbox planet begin | name = TOI-421 | table_ref = }} {{Orbitbox planet | exoplanet = b | mass_earth = {{val|6.7|0.6}} | radius_earth = {{val|2.64|0.08}} | semimajor = {{val|0.0554|0.0010}} | period = {{val|5.197576|0.000005}} | eccentricity = {{val|0.13|0.05}} | inclination = {{val|85.68|0.36|0.46}} }} {{Orbitbox planet | exoplanet = c | mass_earth = {{val|14.1|1.4}} | radius_earth = {{val|5.09|0.07}} | semimajor = {{val|0.1170|0.0018}} | period = {{val|16.067541|0.000004}} | eccentricity = {{val|0.19|0.04}} | inclination = {{val|88.353|0.078|0.084}} }} {{Orbitbox end}} === TOI-421 b === [[File:NASA's James Webb Space Telescope Primed to Lift the Haze Surrounding Sub-Neptunes (51685676732).jpg|thumb|An artist’s concept of TOI-421 b, a [sub-Neptune](/source/sub-Neptune).]] The planet b is a hot [mini-Neptune](/source/mini-Neptune) with a moderate density of {{val|0.37|0.05|u={{rho+}}}} ({{val|2.04|0.28|u=g.cm-3}}){{efn|name=rho_Earth|Density converted from {{rho+}} to g⋅cm−3 by using the value for Earth density {{rho+}} {{=}} {{val|5.513|u=g.cm-3}}.}} and an [equilibrium temperature](/source/Planetary_equilibrium_temperature) of {{val|922|14|u=K}}. Due to its high equilibrium temperature and small mass it is expected to experience significant [atmospheric escape](/source/atmospheric_escape). However, the observed density is not consistent with a thin, hydrogen-depleted atmosphere expected from evolutionary models for a planet forming this close to the star. [Planetary migration](/source/Planetary_migration) is a plausible explanation, meaning that the planet could have formed further away from the star and only more recently moved to current location. TOI-421 b was selected as a [James Webb Space Telescope](/source/James_Webb_Space_Telescope) target early on as a planet similar in size and density to the well-studied sub-Neptune [GJ 1214 b](/source/GJ_1214_b), but thought to be too hot for formation of atmospheric haze, which would allow for bulk chemical characterization of atmosphere. In 2025 it became the first [sub-Neptune](/source/sub-Neptune) around a [solar-type](/source/Solar_analog) star to have its atmosphere characterized with JWST. The observed infrared spectrum is consistent with a [hydrogen](/source/hydrogen)/[helium](/source/helium) dominated atmosphere and detected presence of [water](/source/water) at abundances of {{val|e=-3}}{{nbnd}}{{val|e=-4}} and hints of [sulfur dioxide](/source/sulfur_dioxide) and [carbon monoxide](/source/carbon_monoxide), but no [carbon dioxide](/source/carbon_dioxide) or [methane](/source/methane). The observed spectrum also excludes the possibility of presence of high-altitude haze. This is in contrast to the observed composition of sub-Neptunes around [red dwarf](/source/red_dwarf) stars, which typically show a much higher fraction of heavier gas species. === TOI-421 c === The planet c is a [hot Neptune](/source/hot_Neptune) with a low density of {{val|0.107|0.012|u={{rho+}}}} ({{val|0.590|0.066|u=g.cm-3}}),{{efn|name=rho_Earth}} belonging to the [super-puff](/source/super-puff) class. Its equilibrium temperature is {{val|635|9|u=K}}. Like the planet b, it is also expected to exhibit significant atmospheric escape. However, the low density implies that the planet has retained an extensive atmosphere. == See also == * [HD 152843](/source/HD_152843) * [K2-24](/source/K2-24) == Notes == {{notelist}} == References == {{cite simbad |title=BD-14 1137 |access-date=2025-01-09}} {{cite constellation|TOI-421}} {{cite Gaia DR3|2984582227215748864}} {{cite journal |last1=Høg |first1=E. |last2=Fabricius |first2=C. |last3=Makarov |first3=V. V. |last4=Urban |first4=S. |last5=Corbin |first5=T. |last6=Wycoff |first6=G. |last7=Bastian |first7=U. |last8=Schwekendiek |first8=P. |last9=Wicenec |first9=A. |title=The Tycho-2 catalogue of the 2.5 million brightest stars |journal=Astronomy and Astrophysics |date=March 2000 |volume=355 |pages=L27–L30 |issn=0004-6361 |bibcode=2000A&A...355L..27H}} {{Cite journal |title=The Multiplanet System TOI-421: A Warm Neptune and a Super Puffy Mini-Neptune Transiting a G9 V Star in a Visual Binary |journal=[The Astronomical Journal](/source/The_Astronomical_Journal) |date=2020 |doi=10.3847/1538-3881/aba124|doi-access=free |last1=Carleo |first1=Ilaria |last2=Gandolfi |first2=Davide |last3=Barragán |first3=Oscar |last4=Livingston |first4=John H. |last5=Persson |first5=Carina M. |last6=Lam |first6=Kristine W. F. |last7=Vidotto |first7=Aline |last8=Lund |first8=Michael B. |last9=d'Angelo |first9=Carolina Villarreal |last10=Collins |first10=Karen A. |last11=Fossati |first11=Luca |last12=Howard |first12=Andrew W. |last13=Kubyshkina |first13=Daria |last14=Brahm |first14=Rafael |last15=Oklopčić |first15=Antonija |last16=Mollière |first16=Paul |last17=Redfield |first17=Seth |last18=Serrano |first18=Luisa Maria |last19=Dai |first19=Fei |last20=Fridlund |first20=Malcolm |last21=Borsa |first21=Francesco |last22=Korth |first22=Judith |last23=Esposito |first23=Massimiliano |last24=Díaz |first24=Matías R. |last25=Nielsen |first25=Louise Dyregaard |last26=Hellier |first26=Coel |last27=Mathur |first27=Savita |last28=Deeg |first28=Hans J. |last29=Hatzes |first29=Artie P. |last30=Benatti |first30=Serena |volume=160 |issue=3 |page=114 |arxiv=2004.10095 |bibcode=2020AJ....160..114C |s2cid=216036363 |display-authors=1 }} {{Cite journal |title=Characterisation of the TOI-421 planetary system using CHEOPS, TESS, and archival radial velocity data |journal=[Astronomy & Astrophysics](/source/Astronomy_%26_Astrophysics) |date=2024 |doi=10.1051/0004-6361/202348584 |doi-access=free |last1=Krenn |first1=A. F. |last2=Kubyshkina |first2=D. |last3=Fossati |first3=L. |last4=Egger |first4=J. A. |last5=Bonfanti |first5=A. |last6=Deline |first6=A. |last7=Ehrenreich |first7=D. |last8=Beck |first8=M. |last9=Benz |first9=W. |last10=Cabrera |first10=J. |last11=Wilson |first11=T. G. |last12=Leleu |first12=A. |last13=Sousa |first13=S. G. |last14=Adibekyan |first14=V. |last15=Correia |first15=A. C. M. |last16=Alibert |first16=Y. |last17=Delrez |first17=L. |last18=Lendl |first18=M. |last19=Patel |first19=J. A. |last20=Venturini |first20=J. |last21=Alonso |first21=R. |last22=Anglada |first22=G. |last23=Asquier |first23=J. |last24=Bárczy |first24=T. |last25=Barrado Navascues |first25=D. |last26=Barros |first26=S. C. C. |last27=Baumjohann |first27=W. |last28=Beck |first28=T. |last29=Billot |first29=N. |last30=Bonfils |first30=X. |volume=686 |pages=A301 |arxiv=2404.11074 |bibcode=2024A&A...686A.301K |s2cid=269188184 |display-authors=1 }} {{Cite journal |title=TOI-421 b: A Hot Sub-Neptune with a Haze-Free, Low Mean Molecular Weight Atmosphere |journal=[The Astrophysical Journal Letters](/source/The_Astrophysical_Journal_Letters) |arxiv=2501.01498 |last1=Davenport |first1=Brian |last2=Kempton |first2=Eliza M. -R. |last3=Nixon |first3=Matthew C. |last4=Ih |first4=Jegug |last5=Deming |first5=Drake |last6=Fu |first6=Guangwei |last7=May |first7=E. M. |last8=Bean |first8=Jacob L. |last9=Gao |first9=Peter |last10=Rogers |first10=Leslie |last11=Malik |first11=Matej |date=2025 |s2cid=275324192 |display-authors=1 }} {{Cite web |last1=Carruthers |first1=Margaret W. |last2=Pulliam |first2=Christine |date=2021-11-17 |title=Webb Primed to Lift the Haze Surrounding Sub-Neptunes |url=https://webbtelescope.org/contents/news-releases/2021/news-2021-054 |website=Webb |publisher=[Space Telescope Science Institute](/source/Space_Telescope_Science_Institute)}} {{Lepus (constellation)}}{{Sky|05|27|24.8259|-|14|16|37.046|244.6}} Category:Lepus (constellation) 0421 BD-14 1137 Category:G-type main-sequence stars Category:Planetary systems with two confirmed planets Category:Planetary transit variables --- Adapted from the Wikipedia article [TOI-421](https://en.wikipedia.org/wiki/TOI-421) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/TOI-421?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.