A possible misaligned orbit for the young planet AU Mic c
Journal article, 2025
The AU Microscopii planetary system is only 24 Myr old, and its geometry may provide clues about the early dynamical history of planetary systems. Here, we present the first measurement of the Rossiter–McLaughlin effect for the warm sub-Neptune AU Mic c, using two transits observed simultaneously with the European Southern Observatory’s (ESO’s) Very Large Telescope (VLT)/Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), CHaracterising ExOPlanet Satellite (CHEOPS), and Next-Generation Transit Survey (NGTS). After correcting for flares and for the magnetic activity of the host star, and accounting for transit-timing variations, we find the sky-projected spin–orbit angle of planet c to be in the range λc = 67.8+31.7-49.0 degrees (1σ). We examine the possibility that planet c is misaligned with respect to the orbit of the inner planet b (λb = −2.96 +10.44-10.30), and the equatorial plane of the host star, and discuss scenarios that could explain both this and the planet’s high density, including secular interactions with other bodies in the system or a giant impact. We note that a significantly misaligned orbit for planet c is in some degree of tension with the dynamical stability of the system, and with the fact that we see both planets in transit, though these arguments alone do not preclude such an orbit. Further observations would be highly desirable to constrain the spin–orbit angle of planet c more precisely.
techniques: photometric
stars: activity
techniques: radial velocities
stars: individual: AU Microscopii
planets and satellites: formation
planets and satellites: dynamical evolution and stability
Author
H. Yu
University of Oxford
Z. Garai
HUN-REN-ELTE Exoplanet Research Group
M. Cretignier
University of Oxford
G.M. Szabó
HUN-REN-ELTE Exoplanet Research Group
S. Aigrain
University of Oxford
D. Gandolfi
University of Turin
E. Bryant
University College London (UCL)
A. Correia
Centre for Physics of the University of Coimbra
B. Klein
University of Oxford
A. Brandeker
Stockholm University
James E. Owen
Imperial College London
Maximilian N. Günther
European Space Research and Technology Centre (ESA ESTEC)
J. N. Winn
Princeton University
A. Heitzmann
University of Geneva
H. M. Cegla
University of Geneva
T.G. Wilson
The University of Warwick
S. Gill
The University of Warwick
L. Kriskovics
Hungarian Academy of Sciences
O. Barragán
University of Oxford
Boldog
HUN-REN-ELTE Exoplanet Research Group
L. D. Nielsen
Ludwig Maximilian University of Munich (LMU)
N. Billot
University of Geneva
Marina Lafarga
The University of Warwick
Annabella Meech
University of Oxford
Y. Alibert
University of Bern
R. Alonso
Instituto de Astrofísica de Canarias
T. Bárczy
Admatis
D. Barrado
European Space Astronomy Centre (ESAC)
S.C.C. Barros
University of Porto
W. Baumjohann
Institut fur Weltraumforschung
D. Bayliss
The University of Warwick
W. Benz
University of Bern
M. Bergomi
Istituto nazionale di astrofisica (INAF)
L. Borsato
Istituto nazionale di astrofisica (INAF)
C. Broeg
University of Bern
A. Collier Cameron
University of St Andrews
Szilard Csizmadia
German Aerospace Center (DLR)
P. E. Cubillos
Institut fur Weltraumforschung
Melvyn B. Davies
Lund University
M. Deleuil
Laboratoire d'Astrophysique de Marseille
A. Deline
University of Geneva
O. Demangeon
University of Porto
B.O. Demory
University of Bern
A. Derekas
Eötvös Loránd University (ELTE)
L. Doyle
The University of Warwick
Billy Edwards
Netherlands Institute for Space Research (SRON)
J. A. Egger
Physics Institute
D. Ehrenreich
University of Geneva
Anders Erikson
German Aerospace Center (DLR)
A. Fortier
University of Bern
L. Fossati
Institut fur Weltraumforschung
Malcolm Fridlund
Leiden University
K. Gazeas
University of Athens
Michaël Gillon
University of Liège
M. Gudel
University of Vienna
Ch. Helling
Institut fur Weltraumforschung
K. Isaak
European Space Research and Technology Centre (ESA ESTEC)
L. L. Kiss
Hungarian Academy of Sciences
Judith Korth
Lund University
K. W.F. Lam
German Aerospace Center (DLR)
J. Laskar
Paris Observatory
A. L. des Etangs
Institut d 'Astrophysique de Paris
M. Lendl
University of Geneva
D. Magrin
Istituto nazionale di astrofisica (INAF)
P. Maxted
Keele University
J. McCormac
The University of Warwick
Bruno Merín
European Space Astronomy Centre (ESAC)
C. Mordasini
University of Bern
Valerio Nascimbeni
Istituto nazionale di astrofisica (INAF)
S.M. O’Brien
Queen's University Belfast
G. Olofsson
Stockholm University
R. Ottensamer
University of Vienna
I. Pagano
Istituto nazionale di astrofisica (INAF)
Enric Palle
Instituto de Astrofísica de Canarias
G. Peter
German Aerospace Center (DLR)
D. Piazza
University of Bern
Giampaolo P. Piotto
Istituto nazionale di astrofisica (INAF)
Don L. Pollacco
The University of Warwick
D. Queloz
Swiss Federal Institute of Technology in Zürich (ETH)
Roberto Ragazzoni
Istituto nazionale di astrofisica (INAF)
N. Rando
European Space Research and Technology Centre (ESA ESTEC)
H. Rauer
German Aerospace Center (DLR)
I. Ribas
Institute of Space Sciences (ICE) - CSIC
N. C. Santos
University of Porto
Gaetano Scandariato
Istituto nazionale di astrofisica (INAF)
D. Segransan
University of Geneva
A.E. Simon
University of Bern
A. M.S. Smith
German Aerospace Center (DLR)
S.G. Sousa
University of Porto
R. Southworth
European Space Operations Centre
M. Stalport
University of Liège
M. Steinberger
Institut fur Weltraumforschung
S. Sulis
Laboratoire d'Astrophysique de Marseille
S. Udry
University of Geneva
B. Ulmer
German Aerospace Center (DLR)
S. Ulmer-Moll
University of Geneva
V. Van Grootel
University of Liège
J. Venturini
University of Geneva
E. Villaver
Instituto de Astrofísica de Canarias
N. A. Walton
University of Cambridge
P. J. Wheatley
The University of Warwick
Monthly Notices of the Royal Astronomical Society
00358711 (ISSN) 13652966 (eISSN)
Vol. 536 3 2046-2063Subject Categories (SSIF 2025)
Astronomy, Astrophysics, and Cosmology
DOI
10.1093/mnras/stae2655