Inward migration of the TRAPPIST-1 planets as inferred from their water-rich compositions

Cayman T. Unterborn, Steven Desch, Natalie R. Hinkel, Alejandro Lorenzo

    Research output: Contribution to journalArticle

    12 Citations (Scopus)

    Abstract

    Multiple planet systems provide an ideal laboratory for probing exoplanet composition, formation history and potential habitability. For the TRAPPIST-1 planets, the planetary radii are well established from transits 1,2, with reasonable mass estimates coming from transit timing variations 2,3 and dynamical modelling 4 . The low bulk densities of the TRAPPIST-1 planets demand substantial volatile content. Here we show, using mass-radius-composition models, that TRAPPIST-1f and g probably contain substantial (≥50 wt%) water/ice, with TRAPPIST-1 b and c being significantly drier (≤15 wt%). We propose that this gradient of water mass fractions implies that planets f and g formed outside the primordial snow line whereas b and c formed within it. We find that, compared with planets in our Solar System that also formed within the snow line, TRAPPIST-1b and c contain hundreds more oceans of water. We demonstrate that the extent and timescale of migration in the TRAPPIST-1 system depends on how rapidly the planets formed and the relative location of the primordial snow line. This work provides a framework for understanding the differences between the protoplanetary disks of our Solar System versus M dwarfs. Our results provide key insights into the volatile budgets, timescales of planet formation and migration history of M dwarf systems, probably the most common type of planetary host in the Galaxy.

    Original languageEnglish (US)
    Pages (from-to)297-302
    Number of pages6
    JournalNature Astronomy
    Volume2
    Issue number4
    DOIs
    StatePublished - Apr 1 2018

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    planets
    snow
    water
    transit
    solar system
    histories
    habitability
    radii
    protoplanetary disks
    extrasolar planets
    budgets
    oceans
    ice
    time measurement
    galaxies
    gradients
    estimates

    ASJC Scopus subject areas

    • Astronomy and Astrophysics

    Cite this

    Inward migration of the TRAPPIST-1 planets as inferred from their water-rich compositions. / Unterborn, Cayman T.; Desch, Steven; Hinkel, Natalie R.; Lorenzo, Alejandro.

    In: Nature Astronomy, Vol. 2, No. 4, 01.04.2018, p. 297-302.

    Research output: Contribution to journalArticle

    Unterborn, Cayman T. ; Desch, Steven ; Hinkel, Natalie R. ; Lorenzo, Alejandro. / Inward migration of the TRAPPIST-1 planets as inferred from their water-rich compositions. In: Nature Astronomy. 2018 ; Vol. 2, No. 4. pp. 297-302.
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