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

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

Authors

Ares Osborn

David J Armstrong

Jorge Fernández Fernández

Henrik Knierim

Vardan Adibekyan

Karen A Collins

Elisa Delgado-Mena

Malcolm Fridlund

João Gomes da Silva

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 Ricker

Roland 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



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 $3.20^{+0.16}_{-0.12}$ 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 $9.6^{+1.1}_{-1.3}$ 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.

Journal Article Type Article
Acceptance Date Aug 31, 2023
Online Publication Date Aug 31, 2023
Deposit Date Sep 21, 2023
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 526
Issue 1
Article Number stad2575
Pages 548-566
DOI https://doi.org/10.1093/mnras/stad2575
Keywords Space and Planetary Science, Astronomy and Astrophysics