Exogenous delivery of water to Mercury

Abstract

Radar and spacecraft observations show the permanently shadowed regions around Mercury's North Pole to contain water ice and complex organic material. One possible source of this material are impacts by interplanetary dust particles (IDPs), asteroids, and comets. We have performed numerical simulations of the dynamical evolution of asteroids and comets over the few Myr and checked for their impacts with Mercury. We use the N-body integrator RMVS/Swifter to propagate the Sun and the eight planets from their current positions. We add comets and asteroids to the simulations as massless test particles, based on their current orbital distributions. Asteroid impactors are assigned a probability of being water-rich (C-class) based on the measured distribution of taxonomic types. For comets, we assume a constant water fraction. For IDPs, we use a dynamical meteoroid model to compute the dust flux on Mercury. Relative to previous work on asteroid and comet impacts (Moses et al. 1999), we leverage 20 years of progress in minor body surveys. Immediate post-impact ejection of impactor material into outer space is taken into account as is the migration efficiency of water across Mercury's surface to the polar cold traps. We find that asteroids deliver $\sim 1\times 10^3$ kg/yr of water to Mercury, comets deliver $\sim 1\times 10^3$ kg/yr and IDPs deliver $\sim 16\times 10^3$ kg/yr within a factor of several. Over a timescale of $\sim 1$ Gyr, this is enough to deliver the minimum amount of water required by the radar and MESSENGER observations. While other sources of water on Mercury are not ruled out by our analysis, we show that they are not required to explain the currently available observational lower limits.

38 pages, 10 figures, published in Icarus

References in corpus (6)

• The timeline of the Lunar bombardment - revisited
• Origin and Evolution of Short-Period Comets
• Origin and evolution of long-period comets
• Reconciling the dawn-dusk asymmetry in Mercury's exosphere with the micrometeoroid impact directionality
• The Albedo Distribution of Near Earth Asteroids
• How thick are Mercury's polar water ice deposits?

Cited by in corpus (6)

• Explaining Mercury via a single giant impact is highly unlikely
• Stable Orbits in the Feeding Zone of the Planet Proxima Centauri c
• Delivery of icy planetesimals to inner planets in the Proxima Centauri planetary system
• Growth of the Moon due to bodies ejected from the Earth
• Motion of Planetesimals in the Hill Sphere of the Star Proxima Centauri
• Probabilities of collisions of bodies ejected from forming Earth with the terrestrial planets