# Dust Ablation on the Giant Planets: Consequences for Stratospheric Photochemistry

## TL;DR

This study models dust ablation in giant planet atmospheres, quantifies oxygen influx, and examines resulting photochemistry, revealing implications for atmospheric composition and recent impact history.

## Contribution

It provides the first detailed calculations of dust ablation profiles and oxygen delivery rates to all four giant planets, linking dust influx to observed atmospheric compositions.

## Key findings

- Dust supplies oxygen to giant planets' atmospheres.
- Oxygen delivery is significant for Jupiter and Uranus, but insufficient for Saturn and Neptune.
- Photochemistry alone cannot explain observed CO and H2O abundances.

## Abstract

Ablation of interplanetary dust supplies oxygen to the upper atmospheres of Jupiter, Saturn, Uranus, and Neptune. Using recent dynamical model predictions for the dust influx rates to the giant planets (Poppe, A.R.~et al.~[2016], Icarus 264, 369), we calculate the ablation profiles and investigate the subsequent coupled oxygen-hydrocarbon neutral photochemistry in the stratospheres of these planets. We find that dust grains from the Edgeworth-Kuiper Belt, Jupiter-family comets, and Oort-cloud comets supply an effective oxygen influx rate of 1.0$^{+2.2}_{-0.7} \, \times \, 10^7$ O atoms cm$^{-2}$ s$^{-1}$ to Jupiter, 7.4$^{+16}_{-5.1} \, \times 10^4$ cm$^{-2}$ s$^{-1}$ to Saturn, 8.9$^{+19}_{-6.1} \, \times \, 10^4$ cm$^{-2}$ s$^{-1}$ to Uranus, and 7.5$^{+16}_{-5.1} \, \times \, 10^5$ cm$^{-2}$ s$^{-1}$ to Neptune. The fate of the ablated oxygen depends in part on the molecular/atomic form of the initially delivered products, and on the altitude at which it was deposited. The dominant stratospheric products are CO, H$_2$O, and CO$_2$, which are relatively stable photochemically. Model-data comparisons suggest that interplanetary dust grains deliver an important component of the external oxygen to Jupiter and Uranus but fall far short of the amount needed to explain the CO abundance currently seen in the middle stratospheres of Saturn and Neptune. Our results are consistent with the theory that all of the giant planets have experienced large cometary impacts within the last few hundred years. Our results also suggest that the low background H$_2$O abundance in Jupiter's stratosphere is indicative of effective conversion of meteoric oxygen to CO during or immediately after the ablation process -- photochemistry alone cannot efficiently convert the H$_2$O into CO on the giant planets.