Gas-depleted planet formation occurred in the four-planet system around the red dwarf LHS 1903
Thomas G. Wilson, Anna M. Simpson, Andrew Collier Cameron, Ryan Cloutier, Vardan Adibekyan, Ancy Anna John, Yann Alibert, Manu Stalport, Jo Ann Egger, Andrea Bonfanti, Nicolas Billot, Pascal Guterman, Pierre F. L. Maxted, Attila E. Simon, Sergio G. Sousa, Malcolm Fridlund, Mathias Beck, Anja Bekkelien, Sebastien Salmon, Valerie Van Grootel, Luca Fossati, Alexander James Mustill, Hugh P. Osborn, Tiziano Zingales, Matthew J. Hooton, Laura Affer, Suzanne Aigrain, Roi Alonso, Guillem Anglada, Alexandros Antoniadis-Karnavas, Tamas Barczy, David Barrado Navascues, Susana C. C. Barros, Wolfgang Baumjohann, Thomas Beck, Willy Benz, Federico Biondi, Xavier Bonfils, Luca Borsato, Alexis Brandeker, Christopher Broeg, Lars A. Buchhave, Maximilian Buder, Juan Cabrera, Sebastian Carrazco Gaxiola, David Charbonneau, Sebastien Charnoz, David R. Ciardi, Karen A. Collins, Kevin I. Collins, Rosario Cosentino, Szilard Csizmadia, Patricio E. Cubillos, Shweta Dalal, Mario Damasso, James R. A. Davenport, Melvyn B. Davies, Magali Deleuil, Laetitia Delrez, Olivier D. S. Demangeon, Brice-Olivier Demory, Victoria DiTomasso, Diana Dragomir, Courtney D. Dressing, Xavier Dumusque, David Ehrenreich, Anders Erikson, Emma Esparza-Borges, Andrea Fortier, Izuru Fukuda, Akihiko Fukui, Davide Gandolfi, Adriano Ghedina, Steven Giacalone, Holden Gill, Michael Gillon, Yilen Gomez Maqueo Chew, Manuel Gudel, Pere Guerra, Maximilian N. Gunther, Nathan Hara, Avet Harutyunyan, Yuya Hayashi, Raphaelle D. Haywood, Rae Holcomb, Keith Horne, Sergio Hoyer, Chelsea X. Huang, Masahiro Ikoma, Kate G. Isaak, James A. G. Jackman, Jon M. Jenkins, Eric L. N. Jensen, Daniel Jontof-Hutter, Yugo Kawai, Laszlo L. Kiss, Ben S. Lakeland, Jacques Laskar, David W. Latham, Alain Lecavelier des Etangs, Adrien Leleu, Monika Lendl, Jerome de Leon, Florian Lienhard, Mercedes Lopez-Morales, Christophe Lovis, Michael B. Lund, Rafael Luque, Demetrio Magrin, Luca Malavolta, Aldo F. Martınez Fiorenzano, Andrew W. Mayo, Michel Mayor, Christoph Mordasini, Annelies Mortier, Felipe Murgas, Norio Narita, Valerio Nascimbeni, Belinda A. Nicholson, Goran Olofsson, Roland Ottensamer, Isabella Pagano, Larissa Palethorpe, Enric Palle, Hannu Parviainen, Marco Pedani, Francesco A. Pepe, Gisbert Peter, Matteo Pinamonti, Giampaolo Piotto, Don Pollacco, Ennio Poretti, Didier Queloz, Samuel N. Quinn, Roberto Ragazzoni, Nicola Rando, David Rapetti, Francesco Ratti, Heike Rauer, Federica Rescigno, Ignasi Ribas, Ken Rice, George R. Ricker, Paul Robertson, Thierry de Roche, Laurence Sabin, Nuno C. Santos, Dimitar D. Sasselov, Arjun B. Savel, Gaetano Scandariato, Nicole Schanche, Urs Schroffenegger, Richard P. Schwarz, Sara Seager, Ramotholo Sefako, Damien Segransan, Avi Shporer, Andre M. Silva, Alexis M. S. Smith, Alessandro Sozzetti, Manfred Steller, Gyula M. Szabo, Motohide Tamura, Nicolas Thomas, Amy Tuson, Stephane Udry, Andrew Vanderburg, Roland K. Vanderspek, Julia Venturini, Francesco Verrecchia, Nicholas A. Walton, Christopher A. Watson, Robert D. Wells, Joshua N. Winn, Roberto Zambelli, Carl Ziegler
TL;DR
This study exploits a multi-instrument, multi-technique campaign to characterize a four-planet system around the red dwarf LHS 1903, spanning radii that straddle the M-dwarf radius valley. By combining space-based transit photometry (TESS, CHEOPS) with ground-based follow-up (LCOGT, MuSCAT2/3, SAINT-EX) and HARPS-N radial velocities, the authors determine precise masses and radii for four planets, revealing a rocky inner planet, two with substantial gaseous envelopes, and a gas-depleted outer world. Interior-structure modeling and atmospheric-evolution analysis favor a gas-depleted formation for the outer planet while the inner ones reflect a combined formation-evolution history, better explained by gas-depleted disk scenarios than by thermally driven mass loss alone. Dynamical analyses show long-term stability with potential near-resonant relationships but no strong mean-motion resonance, supporting a formation and evolution narrative in a gas-poor or radially truncated disk in a thick-disk M-dwarf system. Overall, the results provide compelling evidence that gas-depleted formation can yield diverse compositions within a single M-dwarf system and offer a concrete testbed for radius valley theories in low-mass stars.
Abstract
Small exoplanet radii show two populations, referred to as super-Earths and sub-Neptunes, separated by a gap known as the radius valley. This may be produced by the removal of atmospheres due to stellar or internal heating, or lack of an initial envelope. We us transit photometry and radial velocity measurements to detect and characterize four planets orbiting LHS 1903, a red dwarf (M-dwarf) star in the Milky Way's thick disk. The planets have orbital periods between 2.2 and 29.3 days, and span the radius valley within a single planetary system. The derived densities indicate that LHS 1903 b is rocky, while LHS 1903 c and LHS 1903 d have extended atmospheres. Although the most distant planet from the host star, LHS 1903 e, has no gaseous envelope, indicating it formed from gas-depleted material.