Impact events

The Impact Of Cometary Impacts On The Chemistry, Climate, And Spectra Of Hot Jupiter Atmospheres

By Keith Cowing
Status Report
February 9, 2024
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The Impact Of Cometary Impacts On The Chemistry, Climate, And Spectra Of Hot Jupiter Atmospheres
Maps of the wavelength dependent optical depth (on a log scale), with optical depths of 0.1, 1.0 and 10 indicated by dotted/solid/dashed line respectively. We compare the optical depth profiles for an R=10 km, ρ =2 g cm−3 , JWST Ice ver. A cometary composition impact at three different points in time, 1 year (A), 5 years (C), and 25 years (C – steady-state) after impact, with our unperturbed HD209458b reference model (D). To emphasise how the opacity of the atmosphere varies time we also include, on our steady-state opacity map, the 1 year (green), 5 year (blue), 25 year (red) and reference (orange) τ = 1 surfaces as light shading. Note the significant effect that the addition of cometary material has had on the optical depth, in particular how an optical depth of one is reached at lower pressures, averaging ∼ 10−2 bar at steady-state vs ∼ 10−1 bar in the unperturbed model, helping to explain the difference in the transmission spectra seen in Figure 8. — astro-ph.EP

Impacts from icy and rocky bodies have helped shape the composition of solar system objects, for example the Earth-Moon system, or the recent impact of comet Shoemaker-Levy 9 with Jupiter. It is likely that such impacts also shape the composition of exoplanetary systems.

Here we investigate how cometary impacts might affect the atmospheric composition/chemistry of hot Jupiters, which are prime targets for characterisation. We introduce a parametrised cometary impact model that includes thermal ablation and pressure driven breakup, which we couple with the 1D `radiative-convective’ atmospheric model ATMO, including disequilibrium chemistry. We use this model to investigate a wide range of impactor masses and compositions, including those based on observations of Solar System comets, and interstellar ices (with JWST).

We find that even a small impactor (R = 2.5 km) can lead to significant short-term changes in the atmospheric chemistry, including a factor >10 enhancement in H2O, CO, CO2 abundances, and atmospheric opacity more generally, and the near complete removal of observable hydrocarbons, such as CH4, from the upper atmosphere. These effects scale with the change in atmospheric C/O ratio and metallicity. Potentially observable changes are possible for a body that has undergone significant/continuous bombardment, such that the global atmospheric chemistry has been impacted.

Our works reveals that cometary impacts can significantly alter or pollute the atmospheric composition/chemistry of hot Jupiters. These changes have the potential to mute/break the proposed link between atmospheric C/O ratio and planet formation location relative to key snowlines in the natal protoplanetary disc.

Felix Sainsbury-Martinez, Catherine Walsh

Comments: Accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2402.05509 [astro-ph.EP] (or arXiv:2402.05509v1 [astro-ph.EP] for this version)
Submission history
From: Felix Sainsbury-Martinez
[v1] Thu, 8 Feb 2024 09:39:42 UTC (10,150 KB)

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) 🖖🏻