Ices on Mercury: Chemistry of volatiles in permanently cold areas of Mercury's north polar region

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2017-01, Vol.281, p.19-31
• Main Authors: Delitsky, M.L., Paige, D.A., Siegler, M.A., Harju, E.R., Schriver, D., Johnson, R.E., Travnicek, P.
• Format: Article
• Language: English
• Subjects: Craters; Cusps; Fluxes; Freezing; Magnetospheres; Mercury (planet); Mercury surface; Mercury surface ices magnetospheres radiolysis; Photons
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2016.08.006

•Mercury's magnetic field contains magnetic cusps, areas of focused field lines containing trapped magnetospheric charged particles that will be funneled onto the Mercury surface at very high latitudes and direct energetic protons, ions and electrons directly onto ices in the polar regions.•Energy deposition onto the ices comes from magnetospheric charged particles, galactic cosmic rays (GCR), solar energetic particles (SEP) and Lyman-alpha and scattered UV photons.•This focused radiation will initiate chemistry that may create dark compounds that could be the dark low-albedo materials observed by MESSENGER instruments. Thick layers will be created by radiolysis and chemistry as well as gardening, overturn, sputtering and other physical processes occurring simultaneously.•Complex CHNOS molecules may be created by this process, such as aldehydes, amines, alcohols, cyanates, ketones, hydroxides, carbon oxides and suboxides, organic acids and others. Specific compounds are: H2CO, HCOOH, CH3OH, HCO, H2CO3, CH3C(O)CH3, C2O, CxO, C3O2, CxOy, CH3CHO, CH3OCH2CH2OCH3, C2H6, CxHy, NO2, HNO2, HNO3, NH2OH, Na2O, NaOH, HNO, N2H2, N3, HCN, CH3NH2, SO, SO2, SO3, OCS, H2S, CH3SH, even BxHy.•Magnetospheric energy sources dominate the energy flux onto the ices. The total energy fluxes of photons, GCRs and SEPs are each around two or more orders of magnitude less than magnetospheric fluxes. GCR and SEP have lower fluxes but will process deeper layers of the ices because of their greater depth of energy deposition. Observations by the MESSENGER spacecraft during its flyby and orbital observations of Mercury in 2008–2015 indicated the presence of cold icy materials hiding in permanently-shadowed craters in Mercury's north polar region. These icy condensed volatiles are thought to be composed of water ice and frozen organics that can persist over long geologic timescales and evolve under the influence of the Mercury space environment. Polar ices never see solar photons because at such high latitudes, sunlight cannot reach over the crater rims. The craters maintain a permanently cold environment for the ices to persist. However, the magnetosphere will supply a beam of ions and electrons that can reach the frozen volatiles and induce ice chemistry. Mercury's magnetic field contains magnetic cusps, areas of focused field lines containing trapped magnetospheric charged particles that will be funneled onto the Mercury surface at very high latitudes. This magnetic highway will act to