Vapor Production Rates at Ceres from Solar Wind Sputtering

Telescopic observations of dwarf planet Ceres suggest it has a transient water exosphere with an inferred vapor production rate ~10²⁶ H₂O/s when present [1-6]. The water sources and generation mechanism that create this exosphere still remain a topic of much debate. Hypothesized mechanisms include sublimation, cryovolcanism, impacts, and solar-wind sputtering; though none of these mechanisms are mutually exclusive. In this study, we quantify the vapor production rate due to the latter process.

Water ice reservoirs have been detected in three forms at Ceres: exposed surface ice (i.e. impact-related) [7], polar cold traps [8, 9], and a global subsurface ice table [10]. We focus only on surface ice reservoirs (exposed ice and cold traps) since these sources readily allow water molecules to be ejected from the surface. To calculate solar wind sputtering effects, we propagate solar wind data from 1 AU to Ceres’ location for protons <10 keV, which comprises the bulk proton population. We analyze the data for periods during telescopic observations and calculate the sputtering rates. Preliminary results show that although there is an enhancement of the vapor production rate for cases when a solar event is present, production rates are 1-2 orders of magnitude below that reported from telescopic observations.

1. A'Hearn, M. F. and P. D. Feldman (1992), Icarus 98(1): 54-60.

2. Rousselot, P. et al. (2011), ApJ 142(4): 125.

3. Küppers, M. et al. (2014), Nature 505(7484): 525.

4. Roth, L. (2018), Icarus 305: 149-159.

5. Roth, L., et al. (2016), GRL 43(6): 2465-2472.

6. Rousselot, P. et al. (2019), A&A 628: A22.

7. Combe, J.P., et al. (2019), Icarus 318: 22-41.

8. Schorghofer, N., et al. (2016), GRL 43(13): 6783-6789.

9. Platz, T. et al. (2016), Nature Astronomy 1(1): 1-6.

10. Prettyman, T. et al. (2017), Science 355(6320): 55-59.