Upside down: GJ3090 b the first retrograde exoplanet around an M dwarf detected with NIRPS
Abstract
The angle between stellar spin axis and planetary orbital plane can provide key insights into the formation and dynamical evolution of planetary systems. In particular, this measurement in multi-planet systems can be used to further discriminate between different competing migration scenarios. We present six transit observations of the sub-Neptune GJ3090 b obtained with NIRPS and HARPS. GJ3090 b is the inner planet of a confirmed multi-planet system orbiting an M dwarf (M2). Using high spectral resolution and high temporal cadence spectroscopic observations, we analyzed the Rossiter-McLaughlin (RM) effect induced by GJ3090 b to determine its orbital obliquity. Through the RM revolutions technique, we find that the planet is on a retrograde orbit with a derived 3D obliquity of ψ= 136+24−18 deg. We find no evidence of massive outer planetary or wide stellar binary companions, which disfavors scenarios involving gravitational perturbations from a massive body and instead points toward a primordial misalignment of the protoplanetary disk. Our results establish GJ3090 b as the first planet on a retrograde orbit discovered around an M dwarf and the first highly misaligned confirmed multi-planet system without a known massive companion. We further propose late secondary disk accretion around GJ3090, in which the disk is not expected to be aligned with the stellar spin axis, followed by disk-driven migration as the most likely mechanisms to explain the observed architecture. This work also illustrates the capability of the RM revolutions technique when applied to near-infrared data to probe orbital architectures of the smallest planets around M dwarfs that have remained mostly inaccessible.
Versions
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BibTeX
@misc{carteret2026upside,
title = {{Upside down: GJ3090 b the first retrograde exoplanet around an M dwarf detected with NIRPS}},
author = {Y. Carteret and V. Bourrier and L. Parc and A. Winter and R. Allart and I. de Castro Leão and F. Bouchy and V. M. Passegger and C. Cadieux and P. Lamontagne and É. Artigau and F. Baron and S. C. C. Barros and B. Benneke and X. Bonfils and M. Bryan and B. L. Canto Martins and R. Cloutier and E. Cristo and J. Gagné and N. J. Cook and N. B. Cowan and J. R. De Medeiros and X. Delfosse and R. Doyon and X. Dumusque and D. Ehrenreich and J. I. González Hernández and D. Lafrenière and C. Lovis and L. Malo and C. Melo and L. Mignon and C. Mordasini and F. Pepe and R. Rebolo and J. Rowe and N. C. Santos and D. Ségransan and A. Suárez Mascareño and S. Udry and D. Valencia and G. Wade and K. Al Moulla and R. G. de Souza Barros de Amorim and L. Dang and E. Deibert and D. O. Fontinele and T. Forveille and Y. G. C. Frensch and R. de Lima Gomes and D. Mounzer and S. Pelletier and R. Rosener and B. N. Skinner and A. Srivastava and A. K. Stefanov and V. Vaulato and J. P. Wardenier and D. Weisserman},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.24870},
eprint = {2609.24870},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.24870},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Upside down: GJ3090 b the first retrograde exoplanet around an M dwarf detected with NIRPS
AU - Y. Carteret
AU - V. Bourrier
AU - L. Parc
AU - A. Winter
AU - R. Allart
AU - I. de Castro Leão
AU - F. Bouchy
AU - V. M. Passegger
AU - C. Cadieux
AU - P. Lamontagne
AU - É. Artigau
AU - F. Baron
AU - S. C. C. Barros
AU - B. Benneke
AU - X. Bonfils
AU - M. Bryan
AU - B. L. Canto Martins
AU - R. Cloutier
AU - E. Cristo
AU - J. Gagné
AU - N. J. Cook
AU - N. B. Cowan
AU - J. R. De Medeiros
AU - X. Delfosse
AU - R. Doyon
AU - X. Dumusque
AU - D. Ehrenreich
AU - J. I. González Hernández
AU - D. Lafrenière
AU - C. Lovis
AU - L. Malo
AU - C. Melo
AU - L. Mignon
AU - C. Mordasini
AU - F. Pepe
AU - R. Rebolo
AU - J. Rowe
AU - N. C. Santos
AU - D. Ségransan
AU - A. Suárez Mascareño
AU - S. Udry
AU - D. Valencia
AU - G. Wade
AU - K. Al Moulla
AU - R. G. de Souza Barros de Amorim
AU - L. Dang
AU - E. Deibert
AU - D. O. Fontinele
AU - T. Forveille
AU - Y. G. C. Frensch
AU - R. de Lima Gomes
AU - D. Mounzer
AU - S. Pelletier
AU - R. Rosener
AU - B. N. Skinner
AU - A. Srivastava
AU - A. K. Stefanov
AU - V. Vaulato
AU - J. P. Wardenier
AU - D. Weisserman
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2609.24870
UR - https://arxiv.org/abs/2609.24870
AB - The angle between stellar spin axis and planetary orbital plane can provide key insights into the formation and dynamical evolution of planetary systems. In particular, this measurement in multi-planet systems can be used to further discriminate between different competing migration scenarios. We present six transit observations of the sub-Neptune GJ3090 b obtained with NIRPS and HARPS. GJ3090 b is the inner planet of a confirmed multi-planet system orbiting an M dwarf (M2). Using high spectral resolution and high temporal cadence spectroscopic observations, we analyzed the Rossiter-McLaughlin (RM) effect induced by GJ3090 b to determine its orbital obliquity. Through the RM revolutions technique, we find that the planet is on a retrograde orbit with a derived 3D obliquity of ψ= 136^+24_−18 deg. We find no evidence of massive outer planetary or wide stellar binary companions, which disfavors scenarios involving gravitational perturbations from a massive body and instead points toward a primordial misalignment of the protoplanetary disk. Our results establish GJ3090 b as the first planet on a retrograde orbit discovered around an M dwarf and the first highly misaligned confirmed multi-planet system without a known massive companion. We further propose late secondary disk accretion around GJ3090, in which the disk is not expected to be aligned with the stellar spin axis, followed by disk-driven migration as the most likely mechanisms to explain the observed architecture. This work also illustrates the capability of the RM revolutions technique when applied to near-infrared data to probe orbital architectures of the smallest planets around M dwarfs that have remained mostly inaccessible.
ER -