A remnant planetary core in the hot-Neptune desert

Armstrong, David J. and Lopez, Theo A. and Adibekyan, Vardan and Booth, Richard A. and Bryant, Edward M. and Collins, Karen A. and Deleuil, Magali and Emsenhuber, Alexandre and Huang, Chelsea X. ORCID: https://orcid.org/0000-0003-0918-7484 and King, George W. and Lillo-Box, Jorge and Lissauer, Jack J. and Matthews, Elisabeth and Mousis, Olivier and Nielsen, Louise D. and Osborn, Hugh and Otegi, Jon and Santos, Nuno C. and Sousa, Sergio G. and Stassun, Keivan G. and Veras, Dimitri and Ziegler, Carl and Acton, Jack S. and Almenara, Jose M. and Anderson, David R. and Barrado, David and Barros, Susana C. C. and Bayliss, Daniel and Belardi, Claudia and Bouchy, Francois and Briceno, Cesar and Brogi, Matteo and Brown, David J. A. and Burleigh, Matthew R. and Casewell, Sarah L. and Chaushev, Alexander and Ciardi, David R. and Collins, Kevin I. and Colon, Knicole D. and Cooke, Benjamin F. and Crossfield, Ian J. M. and Diaz, Rodrigo F. and Mena, Elisa Delgado and Demangeon, Olivier D. S. and Dorn, Caroline and Dumusque, Xavier and Eigmuller, Philipp and Fausnaugh, Michael and Figueira, Pedro and Gan, Tianjun and Gandhi, Siddharth and Gill, Samuel and Gonzales, Erica J. and Goad, Michael R. and Gunther, Maximilian N. and Helled, Ravit and Hojjatpanah, Saeed and Howell, Steve B. and Jackman, James and Jenkins, James S. and Jenkins, Jon M. and Jensen, Eric L. N. and Kennedy, Grant M. and Latham, David W. and Law, Nicholas and Lendl, Monika and Lozovsky, Michael and Mann, Andrew W. and Moyano, Maximiliano and McCormac, James and Meru, Farzana and Mordasini, Christoph and Osborn, Ares and Pollacco, Don and Queloz, Didier and Raynard, Liam and Ricker, George R. and Rowden, Pamela and Santerne, Alexandre and Schlieder, Joshua E. and Seager, Sara and Sha, Lizhou and Tan, Thiam-Guan and Tilbrook, Rosanna H. and Ting, Eric and Udry, Stephane and Vanderspek, Roland and Watson, Christopher A. and West, Richard G. and Wilson, Paul A. and Winn, Joshua N. and Wheatley, Peter and Villasenor, Jesus Noel and Vines, Jose I. and Zhan, Zhuchang (2020) A remnant planetary core in the hot-Neptune desert. Nature, 583 (7814). ISSN 0028-0836


The interiors of giant planets remain poorly understood. Even for the planets in the Solar System, difficulties in observation lead to large uncertainties in the properties of planetary cores. Exoplanets that have undergone rare evolutionary processes provide a route to understanding planetary interiors. Planets found in and near the typically barren hot-Neptune ‘desert’ (a region in mass–radius space that contains few planets) have proved to be particularly valuable in this regard. These planets include HD149026b, which is thought to have an unusually massive core, and recent discoveries such as LTT9779b and NGTS-4b, on which photoevaporation has removed a substantial part of their outer atmospheres. Here we report observations of the planet TOI-849b, which has a radius smaller than Neptune’s but an anomalously large mass of 39.1−2.6+2.7 Earth masses and a density of 5.2−0.8+0.7 grams per cubic centimetre, similar to Earth’s. Interior-structure models suggest that any gaseous envelope of pure hydrogen and helium consists of no more than 3.9−0.9+0.8 per cent of the total planetary mass. The planet could have been a gas giant before undergoing extreme mass loss via thermal self-disruption or giant planet collisions, or it could have avoided substantial gas accretion, perhaps through gap opening or late formation. Although photoevaporation rates cannot account for the mass loss required to reduce a Jupiter-like gas giant, they can remove a small (a few Earth masses) hydrogen and helium envelope on timescales of several billion years, implying that any remaining atmosphere on TOI-849b is likely to be enriched by water or other volatiles from the planetary interior. We conclude that TOI-849b is the remnant core of a giant planet.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 04 Apr 2022 01:59
Last Modified: 31 May 2022 03:29
Uncontrolled Keywords: desert; helium isotope; Jupiter; Neptune; planet; planetary atmosphere; solar system; Astrophysics - Earth and Planetary Astrophysics; Astrophysics - Solar and Stellar Astrophysics
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Identification Number or DOI: https://doi.org/10.1038/s41586-020-2421-7
URI: http://eprints.usq.edu.au/id/eprint/47439

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