The effect of late giant collisions on the atmospheres of protoplanets and the formation of cold sub-Saturns
| Autor: | Andrew Cumming, M. Ali-Dib, Douglas N. C. Lin |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2021 |
| Předmět: |
Earth and Planetary Astrophysics (astro-ph.EP)
Physics education.field_of_study 010504 meteorology & atmospheric sciences Gas giant Population Uranus FOS: Physical sciences Astronomy and Astrophysics Astrophysics 01 natural sciences Accretion (astrophysics) Jupiter 13. Climate action Space and Planetary Science Neptune Planet 0103 physical sciences Protoplanet education 010303 astronomy & astrophysics 0105 earth and related environmental sciences Astrophysics - Earth and Planetary Astrophysics |
| Popis: | We investigate the origins of cold sub-Saturns (CSS), an exoplanetary population inferred from microlensing surveys. If confirmed, these planets would rebut a theorised gap in planets' mass distribution between those of Neptune and Jupiter caused by the rapid runaway accretion of super-critical 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% the mass of near-runaway envelopes around massive cores can efficiently remove these envelopes entirely via a thermally-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 timescale 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 transformation 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_Earth) cores and less massive (a few M_Earth) 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. Accepted for publication in MNRAS, 17 pages, 9 figures |
| Databáze: | OpenAIRE |
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