TOI-332 b: a super dense Neptune found deep within the Neptunian desert

Ares Osborn*, David J. Armstrong, Jorge Fernández Fernández, Henrik Knierim, Vardan Adibekyan, Karen A. Collins, Elisa Delgado-Mena, Malcolm Fridlund, João Gomes Da Silva, Coel Hellier, David G. Jackson, George W. King, Jorge Lillo-Box, Rachel A. Matson, Elisabeth C. Matthews, Nuno C. Santos, Sérgio G. Sousa, Keivan G. Stassun, Thiam Guan Tan, George R. RickerRoland Vanderspek, David W. Latham, Sara Seager, Joshua N. Winn, Jon M. Jenkins, Daniel Bayliss, Luke G. Bouma, David R. Ciardi, Kevin I. Collins, Knicole D. Colón, Ian J.M. Crossfield, Olivier D.S. Demangeon, Rodrigo F. Díaz, Caroline Dorn, Xavier Dumusque, Marcelo Aron Fetzner Keniger, Pedro Figueira, Tianjun Gan, Robert F. Goeke, Andreas Hadjigeorghiou, Faith Hawthorn, Ravit Helled, Steve B. Howell, Louise D. Nielsen, Hugh P. Osborn, Samuel N. Quinn, Ramotholo Sefako, Avi Shporer, Paul A. Strøm, Joseph D. Twicken, Andrew Vanderburg, Peter J. Wheatley

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

To date, thousands of planets have been discovered, but there are regions of the orbital parameter space that are still bare. An example is the short period and intermediate mass/radius space known as the 'Neptunian desert', where planets should be easy to find but discoveries remain few. This suggests unusual formation and evolution processes are responsible for the planets residing here. We present the discovery of TOI-332 b, a planet with an ultra-short period of 0.78 d that sits firmly within the desert. It orbits a K0 dwarf with an effective temperature of 5251 ± 71 K. TOI-332 b has a radius of R, smaller than that of Neptune, but an unusually large mass of 57.2 ± 1.6 M. It has one of the highest densities of any Neptune-sized planet discovered thus far at g cm-3. A 4-layer internal structure model indicates it likely has a negligible hydrogen-helium envelope, something only found for a small handful of planets this massive, and so TOI-332 b presents an interesting challenge to planetary formation theories. We find that photoevaporation cannot account for the mass-loss required to strip this planet of the Jupiter-like envelope it would have been expected to accrete. We need to look towards other scenarios, such as high-eccentricity migration, giant impacts, or gap opening in the protoplanetary disc, to try and explain this unusual discovery.

Original languageEnglish
Pages (from-to)548-566
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Volume526
Issue number1
DOIs
StatePublished - 1 Nov 2023
Externally publishedYes

Keywords

  • planets and satellites: detection
  • planets and satellites: individual: (TOI-332, TIC 139285832)

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