Volcanism on Mercury as a tool for determining its evolution, internal composition and origin

1. Volcanism on Mercury asa tool for determining itsevolution, internal composition and origin David Rothery, Dept of Earth & Environmental Sciences The Open University D.A.Rothery@open.ac.uk With thanks to the ESA Mercury Surface & Composition Working Group

2. Missions:Mariner 10 flybys 1973-4 MESSENGER flybys 2008-9, orbit 2011-12 BepiColombo orbit 2020-2021 KEY FACT: despite very large, presumably iron-rich, core, Mercury’s surface has <3 wt% FeO

5. Primary & Secondary crust defined by Taylor, S. R. (1982, 1989)

7. Lunar crust examples Mixed crust types(if you don’t recognise the distinction!) Primary crust (70% of nearside) Secondary crust (30% of nearside)

8. ‘Average crust’: • reflects arbitrary proportions of exposedareas of primary and secondary crust • conflates two entirely different processesof crust-formation • We cannot back-track from crust composition to mantle composition unless we: • recognise how the crust formed • measure and model primary crust • and secondary crust separately

9. BepiColombo: Mercury Imaging X-ray Spectrometer MIXS Spatial resolution 10s to 100s kmdepending on abundance and solar state

11. <100 km> Raditladi

14. < 100 km >

15. Caloris basin

16. < 100 km >

17. pi Matisse pi Matisse ejecta overlies intercrater plains Primarycrust exposedin walls? Embays Matisseejecta < 200 km >

18. Look for primary crust here ? Matisse-fill lava post-Matisse ejecta ps lava Matisse ejecta pi lava Primary crust