Mercury’s Plains and Volcanism Jake Turner PTYS 395
Dec 15, 2015
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
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 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.
A
Tolstoj Basin
Intercrater 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 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