Mercury’s Plains and Volcanism

Jake TurnerPTYS 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 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