J/A+A/699/A344ivo://CDS.VizieR/J/A+A/699/A344doi:10.26093/cds/vizier.36990344CDSCastro-Gonzalez A.Bouchy F.Correia A.C.M.Sozzetti A.Lillo-Box J.,Figueira P.Lavie B.Lovis C.Hobson M.J.Sousa S.G.Adibekyan V.,Standing M.R.Hara N.C.Barrado D.Silva A.M.Bourrier V.Korth J.,Santos N.C.Damasso M.Zapatero Osorio M.R.Rodrigues J.Alibert Y.,Barros S.C.C.Cristiani S.Di Marcantonio P.Gonzalez Hernandez J.I.,Lo Curto G.Martins C.J.A.P.Nunes N.J.Palle E.Pepe F.,Suarez Mascareno A.Tabernero H.M.2025-08-01T20:03:24Z2025-07-22T09:33:30ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frmultiple-starsexoplanetsphotometryvisible-astronomyradial-velocityspectroscopyThe formation and evolution of ultra-short-period (USP) rocky planets is poorly understood. However, it is widely thought that these planets could not have formed at their present-day close-in orbits, but instead migrated inwards through interactions with outer neighbours. We aim to confirm and characterise the USP Earth-sized validated planet K2-157 b (P_orb_=8.8h) and constrain the presence of additional companions in the system through radial velocity (RV) measurements. We measured 49 RVs with the ESPRESSO spectrograph and tested different planetary and non-planetary configurations to infer the model that best represents our data set. We derived the orbital and physical properties of the system through a global RV and transit model. We detected two additional super-Neptune-mass planets located within the warm Neptunian savanna, K2-157 c (P_orb,c_=25.942^+0.045^_-0.044_d, M_p,c_sini=30.8+/-1.9M_{Earth}_) and K2-157 d (P_orb,d_=66.50^+0.71^_-0.59_d, M_p,d_sini=23.3+/-2.5M_{Earth}_). The joint analysis constrains the mass of K2-157 b at the 2.8{sigma} level, M_p,b}_=1.14^+0.41^_-0.42_M_{Earth}_ (<2.4M_{Earth}_ at 3{sigma}), which, together with the inferred radius, R_p_=0.935+/-0.090R_{Earth}_, make the planet compatible with a rocky composition with a likely (68% confidence) higher iron-to-silicate mass fraction than Earth. K2 data discard non-grazing transit configurations for K2-157 c (i_c_<88.4{deg} at 3{sigma}), and ESPRESSO data constrain the eccentricities of K2-157 c and K2-157 d to e_c_<0.2 and e_d_<0.5 at 3{sigma}. Our dynamical analysis indicates that the system is stable for eccentricities up to e_c_, e_d_~0.3 and mutual inclinations up to ~60{deg}. At a population level, we find that the trend that the closest USP planets tend to orbit late-type stars does not hold when scaling the orbital separation to the Roche limit, which suggests that the orbital distribution of the closest planets across spectral types is primarily determined by tidal disruption. The orbital architecture of K2-157 is unusual in the known exoplanet plethora, with only one similar case reported to date: 55 Cnc. The USP planets of these systems, being accompanied by massive, long-period, relatively spaced, and possibly misaligned neighbours, could have migrated inwards through eccentricity-based mechanisms triggered by secular interactions.2025A&A...699A.344Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/699/A344CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/699/A344https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/699/A344http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/699/A344https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/699/A344https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/699/A344http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/699/A344GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/A+A/699/A344/tableb1K2 everest photometry of K2-157 (Campaign 10)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTimeBaricentric Julian date (BJD)dtime.epochdoubleFluxK2 everest normalised fluxphot.flux;arith.ratiodoubleCampaign[C10] K2 Campaignmeta.idcharJ/A+A/699/A344/tableb2TESS PDCSAP photometry of K2-157 (Sector 46)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTimeBaricentric Julian date (BJD)dtime.epochdoubleindexedFlux? TESS PDCSAP fluxphot.flux.density;em.optdoublenullablee_Flux? TESS PDCSAP flux errorstat.error;phot.fluxdoublenullableSector[S46] TESS Sectorobs.fieldcharJ/A+A/699/A344/tableb3ESPRESSO radial velocities of K2-157 obtained under the programs 1102.C-0744, 1102.C-0958, 1104.C-0350, and 106.21M2.004recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBJDBaricentric Julian datedtime.epochdoubleRVDRSRadial velocity from the DRSm/sphys.veloc;pos.heliocentricdoublee_RVDRSRadial velocity error from the DRSm/sstat.errordoubleRVsbartRadial velocity from sbartm/sphys.veloc;pos.heliocentricdoublee_RVsbartRadial velocity error from sbartm/sstat.errordoubleFWHMFull width at half maximum (FWHM) of the cross-correlation function (CCF)m/sstat.correlationdoublee_FWHMError of the full width at half maximum (FWHM) of the cross-correlation function (CCF)m/sstat.error;phys.angSizedoubleBISBisector spanm/sphys.velocdoublee_BISBisector span errorm/sstat.errordoubleContrastContrast of the cross-correlation function (CCF)%phot.flux;arith.ratiodoublee_ContrastError of the contrast of the cross-correlation function (CCF)%stat.errordoubleHalphaH{alpha} line depthphot.flux.density;arith.ratiodoublee_HalphaH{alpha} line depth errorstat.error;spect.linedoubleNaSodium line depthphot.flux.density;arith.ratiodoublee_NaSodium line depth errorstat.errordoubleCaCalcium line depthphot.flux.density;arith.ratiodoublee_CaCalcium line depth errorstat.errordouble