The effect of late giant collisions on the atmospheres of protoplanets and the foation of cold sub-Saturns

Mohamad Ali-Dib, Andrew Cumming, Douglas N.C. Lin

    Research output: Contribution to journalArticlepeer-review


    We investigate the origins of cold sub-Saturns (CSSs), an exoplanetary population inferred from microlensing surveys. If confied, these planets would rebut a theorized gap in planets' mass distribution between those of Neptune and Jupiter caused by the rapid runaway accretion of supercritical cores. In an attempt to resolve this theoretical-observational disparity, we examine the outcomes of giant collisions between sub-critical protoplanets. Due to the secular interaction among protoplanets, these events may occur in rapidly depleting discs. We show that impactors 5 per cent the mass of near-runaway envelopes around massive cores can efficiently remove these envelopes entirely via a theally driven super-Eddington wind emanating from the core itself, in contrast with the stellar Parker winds usually considered. After a brief cooling phase, the merged cores resume accretion. But, the evolution time-scale of transitional discs is too brief for the cores to acquire sufficiently massive envelopes to undergo runaway accretion despite their large combined masses. Consequently, these events lead to the emergence of CSS without their transfoation into gas giants. We show that these results are robust for a wide range of disc densities, grain opacities, and silicate abundance in the envelope. Our fiducial case reproduces CSS with heavy (30 M) cores and less massive (a few M) sub-critical envelopes. We also investigate the other limiting cases, where continuous mergers of comparable-mass cores yield CSS with wider ranges of core-to-envelope mass ratios and envelope opacities. Our results indicate that it is possible for CSS and Uranus and Neptune to emerge within the framework of well-studied processes, and they may be more common than previously postulated.

    Original languageEnglish (US)
    Pages (from-to)1413-1431
    Number of pages19
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number1
    StatePublished - Jan 1 2022


    • atmospheres
    • foation
    • planets and satellites
    • planets and satellites

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science


    Dive into the research topics of 'The effect of late giant collisions on the atmospheres of protoplanets and the foation of cold sub-Saturns'. Together they form a unique fingerprint.

    Cite this