Exoplanetology: Exoplanets & Exomoons

Impacting Atmospheres: How Late-Stage Pollution Alters Exoplanet Composition

By Keith Cowing
Status Report
astro-ph.EP
September 24, 2024
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Impacting Atmospheres: How Late-Stage Pollution Alters Exoplanet Composition
We compare the radial profile of deposited mass of impactors (left and middle columns) and the final metallicity (deposited mass / gas mass only in H and He; right column) in atmospheres of varying initial metallicity Z. The left and middle panels show the mass deposited by a 10 m impactor as a function of the planet’s radius and atmospheric pressure respectively. The upper panels depict SiO2 at 0.1 au and the lower panels depict H2O at 3.5 au. All atmospheric profiles have fgas = 10−2 and fsolid = 10−5 . Pentacles indicate the advective-radiative boundary — astro-ph.EP

Atmospheric composition of exoplanets is often considered as a probe of the planet’s formation condition. How exactly the initial chemical memory may be altered from the birth to the final state of the planet, however, remains unknown.

Here, we develop a simple model of pollution of planetary atmosphere by the vaporization of infalling planetesimal of varying sizes and composition (SiO2 inside 1 au and H2O outside 1 au), following their trajectory and thermal evolution through the upper advective and radiative layers of a sub-Neptune class planet during the late stage of disk evolution.

We vary the rate of pollution by changing the solid content of the disk and by dialing the level of disk gas depletion which in turn determines the rate of planetary migration. We find that pollution by silicate grains will always be limited by the saturation limit set by the thermal state of the atmosphere.

By contrast, pollution by water ice can lead to ∼2–4 orders of magnitude variation in the atmospheric water mass fraction depending on the solid and gas content of the disk. Both cases suggest that post-formation pollution can erase the initial compositional memory of formation.

Post-formation pollution can potentially transform sub-Neptunes with H/He-dominated envelope that initially formed beyond the iceline to waterworlds (water-enriched envelope) when the disk gas is depleted by ≳2 orders of magnitude, allowing gentle migration.

We additionally discuss the expected C/O ratio profile under pollution by water and refractory carbon species.

Emilia Vlahos, Yayaati Chachan, Vincent Savignac, Eve J. Lee

Comments: Under review at ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2409.13820 [astro-ph.EP] (or arXiv:2409.13820v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2409.13820
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Submission history
From: Eve Lee
[v1] Fri, 20 Sep 2024 18:01:13 UTC (1,135 KB)
https://arxiv.org/abs/2409.13820
Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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