ERTH 2020 Study Guide - Final Guide: Caloris Planitia, Effective Temperature, Axial Tilt
23 May 2018
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Mercury
• The planet mercury is hard to see because it’s too close to the sun, too small and doesn’t
have an atmosphere
• It’s easiest to see when at maximum elongation
• Missions to mercury
o Messenger
o Mariner flyby
• Comparison of the Moon and Mercury
o No atmosphere
o Similar diameter
o Gravity is stronger on Mercury
o Mass is different → Mercury 4.5 times more mass than the Moon
• Moon has 1.2% of the Earth’s mass and is 1/3 dense so it’s composed of dense rocks (no
continental crusts)
• Mercury has 5.3% of the Earth’s mass and is almost as dense…how is that possible?
o The Core of Mercury is almost as large as the Earth’s despite that it is much
smaller
o This accounts for the density
• No axial tilt compared to the Earth
o Mercury does not have seasons – the poles do not see light
• Elliptical orbit similar to the Earth
o It has a higher eccentricity 34% difference in variation on either side of the Sun
• Mercury has a much higher surface temperature than we would expect
o Effective temperature: an estimate of the surface temp of a planet based on its
distance from the sun
• Surface topography
o Mercury and the Moon has similar height distributions
o Similar crustal histories
• Features and Structures – impact craters suggest older and younger terranes
o Northern plains
o Central highlands
o New craters
o Impact basins – Caloris Basin
• Lava
o Flood lavas found in the polar northern plains
o Smoother topographic terrane with less craters – therefore younger
o Non-viscous magmatic rocks
• Surface structures – ridges and faults
o Compression from thermal contraction of the solid crust
o Not plate tectonics
• Caloris Basin
o Created from a large impact 3.8 billion years ago
o There are surface disruptions at the antipode as expected with a large impact
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