Mercury s Plains and Volcanism Jake Turner PTYS 395 Overview What are plains What types of plains does Mercury have Origins of the plains Volcanism How will MESSENGER help What are Plains Flat or smoothly undulating surfaces They are a canvas on which other landforms devolve Plains are evidence for resurfacing or the creation of a smooth surface from a rough surface Plains on Mercury About 60 of Mercury is believed to be plains Most abundant terrain on Mercury More widespread and higher albedo than plains on the moon Types of Plains Intercrater Heavily cratered Older then smooth 45 of surface is covered by intercrater plains Smooth Plains Occur in the highlands between clusters of craters Young Confined to interior and exterior of impact basins and large craters 15 of surface Examples of Intercrater Plains Examples of Smooth Plains Intercrater Plains Located between and around clusters of large craters in the heavily cratered highlands Age around the period of the heavy bombardment 4 4 2 billion years old Volume of plains decreased as age decreased Craters less then 50km may have been destroyed by the intercrater plains formation Smooth Plains Two large concentrations Caloris Basin Borealis Basin 90 are associated with older large impact basins Similar to lunar Maria Age 3 8 billions years End of heavy bombardment Origins of the Plains 1 Impact Crater Ejecta deposits from large basins Consists of two parts A continuous ejecta blanket Discontinues ejecta beyond the continuous ejecta 2 Volcanic deposits Origins of the Smooth Plains Impact Ejecta Theory Smooth plains around the Caloris basin would be smooth ejecta deposits Interior smooth plains would be impact melt Other plains would be impact eject or impact melt Problem with Impact Ejecta Cannot explain why the plains cover 15 of the surface compared to 5 on the moon Problems with the Impact Ejecta Theory Cannot explain why the plains cover 15 of the surface compared to 5 on the moon For example Smooth plains around Caloris basin extend 2000km No such extensive eject deposits exist on the moon Mercury has higher surface gravity then moon Smooth Plains Volcanism Smooth plains are younger than the basins they occupy or surround Embayments are a common feature of lava flows Isn t definitive though still need composition Smooth Plain Volcanism Earth based radar observations show that the annulus of smooth plains surrounding Caloris is like the Lunar Maria Color images of Tolstoj basin suggest different composition A Tolstoj Basin Intercrater Plains Volcanic Covers 45 of the surface No evidence of source basins The frequency of the interior morphologies of craters on the intercrater plains is the same as the lunar Maria Volcanic Intercrater Plains Recalibrated data from Mariner 10 suggest that plains have different composition age and grain size than the surroundings Problems with Volcanism Because of Mariner 10 s bad lighting and resolution conditions volcanic landforms are difficult to find Composition not know exactly How Messenger will help Better resolution Experience with lighting conditions Analyze composition more thoroughly and fully Early data analysis might suggest relatively recent volcanism Biblography R G StroR G Strom A L Sprague Exploring Mercury The Iron Planet Springer New York 2003 Kiefer Walter and Murray Brue Formation of Mercury s Smooth Plains Pasadena California 1987 G Jeffrey Taylor Mercury Unveiled Hawaii s Institute of Geophysics and Planetology University of Hawaii http solarsystem nasa gov scitech display cfm T ID 365