Mercury’s Plains and VolcanismOverviewWhat are Plains?Plains on MercuryTypes of PlainsExamples of Intercrater PlainsExamples of Smooth PlainsIntercrater PlainsSmooth PlainsOrigins of the PlainsOrigins of the Smooth PlainsProblems with the Impact Ejecta TheorySmooth Plains VolcanismSmooth Plain VolcanismIntercrater Plains VolcanicVolcanic Intercrater PlainsProblems with VolcanismHow Messenger will help?BiblographyMercury’s Plains and VolcanismJake TurnerPTYS 395Overview •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 surfacePlains 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 surfaceExamples of Intercrater PlainsExamples of Smooth PlainsIntercrater 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 bombardmentOrigins of the Plains1. Impact Crater Ejecta deposits from large basins •Consists of two parts –A continuous ejecta blanket –Discontinues ejecta beyond the continuous ejecta. 2. Volcanic depositsOrigins of the Smooth PlainsImpact 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 PlainsVolcanism •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. ATolstoj BasinIntercrater PlainsVolcanic •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 exactlyHow 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.