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  The nature of the giant exomoon candidate Kepler-1625 b-i

Heller, R. (2018). The nature of the giant exomoon candidate Kepler-1625 b-i. Astronomy and Astrophysics, 610: A39. doi:10.1051/0004-6361/201731760.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0000-B385-F Version Permalink: http://hdl.handle.net/21.11116/0000-0000-B3A1-F
Genre: Journal Article

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 Creators:
Heller, René1, Author              
Affiliations:
1Department Solar and Stellar Interiors, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832287              

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Free keywords: accretion, accretion disks / eclipses / planetary systems / planets and satellites: composition / planets and satellites: formation / planets and satellites: individual: Kepler-1625 b
 MPIS_GROUPS: Solar and Stellar Interiors
 MPIS_PROJECTS: Plato
 Abstract: The recent announcement of a Neptune-sized exomoon candidate around the transiting Jupiter-sized object Kepler-1625 b could indicate the presence of a hitherto unknown kind of gas giant moon, if confirmed. Three transits of Kepler-1625 b have been observed, allowing estimates of the radii of both objects. Mass estimates, however, have not been backed up by radial velocity measurements of the host star. Here we investigate possible mass regimes of the transiting system that could produce the observed signatures and study them in the context of moon formation in the solar system, i.e., via impacts, capture, or in-situ accretion. The radius of Kepler-1625 b suggests it could be anything from a gas giant planet somewhat more massive than Saturn (0.4 MJup) to a brown dwarf (BD; up to 75 MJup) or even a very-low-mass star (VLMS; MJup ≈ 0.11 M). The proposed companion would certainly have a planetary mass. Possible extreme scenarios range from a highly inflated Earth-mass gas satellite to an atmosphere-free water–rock companion of about 180 M. Furthermore, the planet–moon dynamics during the transits suggest a total system mass of 17.6−12.6+19.2 MJup. A Neptune-mass exomoon around a giant planet or low-mass BD would not be compatible with the common mass scaling relation of the solar system moons about gas giants. The case of a mini-Neptune around a high-mass BD or a VLMS, however, would be located in a similar region of the satellite-to-host mass ratio diagram as Proxima b, the TRAPPIST-1 system, and LHS 1140 b. The capture of a Neptune-mass object around a 10 MJup planet during a close binary encounter is possible in principle. The ejected object, however, would have had to be a super-Earth object, raising further questions of how such a system could have formed. In summary, this exomoon candidate is barely compatible with established moon formation theories. If it can be validated as orbiting a super-Jovian planet, then it would pose an exquisite riddle for formation theorists to solve.

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Language(s): eng - English
 Dates: 2018-02-282018
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Method: Peer
 Identifiers: DOI: 10.1051/0004-6361/201731760
 Degree: -

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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
 Creator(s):
Affiliations:
Publ. Info: Berlin : Springer-Verlag
Pages: - Volume / Issue: 610 Sequence Number: A39 Start / End Page: - Identifier: ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1