TY - JOUR
T1 - TOI-6478 b
T2 - A cold underdense Neptune transiting a fully convective M dwarf from the thick disc
AU - Scott, Madison G.
AU - Triaud, Amaury H.M.J.
AU - Barkaoui, Khalid
AU - Sebastian, Daniel
AU - Burgasser, Adam J.
AU - Collins, Karen A.
AU - Dransfield, Georgina
AU - Hellier, Coel
AU - Howell, Steve B.
AU - Piette, Anjali A.A.
AU - Rackham, Benjamin V.
AU - Stassun, Keivan G.
AU - Stokholm, Amalie
AU - Timmermans, Mathilde
AU - Watkins, Cristilyn N.
AU - Fausnaugh, Michael
AU - Fukui, Akihiko
AU - Jenkins, Jon M.
AU - Narita, Norio
AU - Ricker, George
AU - Softich, Emma
AU - Schwarz, Richard P.
AU - Seager, Sara
AU - Shporer, Avi
AU - Theissen, Christopher
AU - Twicken, Joseph D.
AU - Winn, Joshua N.
AU - Watanabe, David
N1 - Publisher Copyright:
© 2025 The Author(s).
PY - 2025/6/1
Y1 - 2025/6/1
N2 - Growing numbers of exoplanet detections continue to reveal the diverse nature of planetary systems. Planet formation around late-type M dwarfs is of particular interest. These systems provide practical laboratories to measure exoplanet occurrence rates for M dwarfs, thus testing how the outcomes of planet formation scale with host mass, and how they compare to Sun-like stars. Here, we report the discovery of TOI-6478 b, a cold (K) Neptune-like planet orbiting an M5 star (,, K) that is a member of the Milky Way's thick disc. We measure a planet radius of on a d orbit. Using radial velocities, we calculate an upper mass limit of (, with confidence. TOI-6478 b is a milestone planet in the study of cold Neptune-like worlds. Due to its large atmospheric scale height, it is amenable to atmospheric characterization with facilities such as JWST, and will provide an excellent probe of atmospheric chemistry in this cold regime. It is one of very few transiting exoplanets that orbit beyond their system's ice-line whose atmospheric chemical composition can be measured. Based on our current understanding of this planet, we estimate TOI-6478 b's spectroscopic features (in transmission) can be as high as the widely studied planet K2-18 b.
AB - Growing numbers of exoplanet detections continue to reveal the diverse nature of planetary systems. Planet formation around late-type M dwarfs is of particular interest. These systems provide practical laboratories to measure exoplanet occurrence rates for M dwarfs, thus testing how the outcomes of planet formation scale with host mass, and how they compare to Sun-like stars. Here, we report the discovery of TOI-6478 b, a cold (K) Neptune-like planet orbiting an M5 star (,, K) that is a member of the Milky Way's thick disc. We measure a planet radius of on a d orbit. Using radial velocities, we calculate an upper mass limit of (, with confidence. TOI-6478 b is a milestone planet in the study of cold Neptune-like worlds. Due to its large atmospheric scale height, it is amenable to atmospheric characterization with facilities such as JWST, and will provide an excellent probe of atmospheric chemistry in this cold regime. It is one of very few transiting exoplanets that orbit beyond their system's ice-line whose atmospheric chemical composition can be measured. Based on our current understanding of this planet, we estimate TOI-6478 b's spectroscopic features (in transmission) can be as high as the widely studied planet K2-18 b.
KW - planets and satellites: detection
KW - planets and satellites: fundamental parameters
KW - planets and satellites: gaseous planets
KW - stars: low-mass
UR - https://www.scopus.com/pages/publications/105008066018
UR - https://www.scopus.com/pages/publications/105008066018#tab=citedBy
U2 - 10.1093/mnras/staf684
DO - 10.1093/mnras/staf684
M3 - Article
AN - SCOPUS:105008066018
SN - 0035-8711
VL - 540
SP - 1909
EP - 1927
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -