TOI-1634 b: An Ultra-short-period Keystone Planet Sitting inside the M-dwarf Radius Valley

Cloutier, RyanRyanCloutierCharbonneau, DavidDavidCharbonneauStassun, Keivan G.Keivan G.StassunMurgas, FelipeFelipeMurgasMortier, AnneliesAnneliesMortierMassey, RobertRobertMasseyLissauer, Jack J.Jack J.LissauerLatham, David W.David W.LathamIrwin, JonathanJonathanIrwinHaywood, Raphaëlle D.Raphaëlle D.HaywoodGuerra, PerePereGuerraGirardin, EricEricGirardinGiacalone, Steven A.Steven A.GiacaloneBosch-Cabot, PauPauBosch-CabotBieryla, AllysonAllysonBierylaWinn, JoshuaJoshuaWinnWatson, Christopher A.Christopher A.WatsonVanderspek, RolandRolandVanderspekUdry, StéphaneStéphaneUdryTamura, MotohideMotohideTamuraSOZZETTI, AlessandroAlessandroSOZZETTIShporer, AviAviShporerSégransan, DamienDamienSégransanSeager, SaraSaraSeagerSavel, Arjun B.Arjun B.SavelSasselov, DimitarDimitarSasselovRose, MarkMarkRoseRicker, GeorgeGeorgeRickerRice, KenKenRiceQuintana, Elisa V.Elisa V.QuintanaQuinn, Samuel N.Samuel N.QuinnPIOTTO , GIAMPAOLOGIAMPAOLOPIOTTOPhillips, DavidDavidPhillipsPepe, FrancescoFrancescoPepePedani, MarcoMarcoPedaniParviainen, HannuHannuParviainenPalle, EnricEnricPalleNarita, NorioNorioNaritaMOLINARI, Emilio CarloEmilio CarloMOLINARIMICELA, GiuseppinaGiuseppinaMICELAMcDermott, ScottScottMcDermottMayor, MichelMichelMayorMatson, Rachel A.Rachel A.MatsonMartinez Fiorenzano, Aldo F.Aldo F.Martinez FiorenzanoLovis, ChristopheChristopheLovisLópez-Morales, MercedesMercedesLópez-MoralesKusakabe, NobuhikoNobuhikoKusakabeJensen, Eric L. N.Eric L. N.JensenJenkins, Jon M.Jon M.JenkinsHuang, Chelsea X.Chelsea X.HuangHowell, Steve B.Steve B.HowellHARUTYUNYAN, AVETAVETHARUTYUNYANFűrész, GáborGáborFűrészFukui, AkihikoAkihikoFukuiEsquerdo, Gilbert A.Gilbert A.EsquerdoEsparza-Borges, EmmaEmmaEsparza-BorgesDumusque, XavierXavierDumusqueDressing, Courtney D.Courtney D.DressingFabrizio, Luca DiLuca DiFabrizioCollins, Karen A.Karen A.CollinsCameron, Andrew CollierAndrew CollierCameronChristiansen, Jessie L.Jessie L.ChristiansenCecconi, MassimoMassimoCecconiBuchhave, Lars A.Lars A.BuchhaveBoschin, WalterWalterBoschinANDREUZZI, GloriaGloriaANDREUZZI2022-03-292022-03-2920210004-6256http://hdl.handle.net/20.500.12386/32031Studies of close-in planets orbiting M dwarfs have suggested that the M-dwarf radius valley may be well explained by distinct formation timescales between enveloped terrestrials and rocky planets that form at late times in a gas-depleted environment. This scenario is at odds with the picture that close-in rocky planets form with a primordial gaseous envelope that is subsequently stripped away by some thermally driven mass-loss process. These two physical scenarios make unique predictions of the rocky/enveloped transition's dependence on orbital separation such that studying the compositions of planets within the M-dwarf radius valley may be able to establish the dominant physics. Here, we present the discovery of one such keystone planet: the ultra-short-period planet TOI-1634 b (P = 0.989 days, $F=121{F}_{\oplus }$, ${r}_{p}={1.790}_{-0.081}^{+0.080}$ R⊕) orbiting a nearby M2 dwarf (Ks = 8.7, Rs = 0.450 R⊙, Ms = 0.502 M⊙) and whose size and orbital period sit within the M-dwarf radius valley. We confirm the TESS-discovered planet candidate using extensive ground-based follow-up campaigns, including a set of 32 precise radial velocity measurements from HARPS-N. We measure a planetary mass of ${4.91}_{-0.70}^{+0.68}$ M⊕, which makes TOI-1634 b inconsistent with an Earth-like composition at $5.9\sigma $ and thus requires either an extended gaseous envelope, a large volatile-rich layer, or a rocky composition that is not dominated by iron and silicates to explain its mass and radius. The discovery that the bulk composition of TOI-1634 b is inconsistent with that of Earth supports the gas-depleted formation mechanism to explain the emergence of the radius valley around M dwarfs with ${M}_{s}\lesssim 0.5$ M⊙.STAMPAenTOI-1634 b: An Ultra-short-period Keystone Planet Sitting inside the M-dwarf Radius ValleyArticle10.3847/1538-3881/ac01572-s2.0-85113303932https://api.elsevier.com/content/abstract/scopus_id/85113303932https://iopscience.iop.org/article/10.3847/1538-3881/ac01572021AJ....162...79CFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation