AST 111 Lecture Notes - Lecture 14: Mariner 10, Caloris Planitia, Runaway Greenhouse Effect

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Published on 22 Oct 2015
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AST 111: Lecture 14-Mercury, Venus and Mars
-Mercury is cratered like the Moon
Nearly everything known about Mercury has been learned using two spacecraft
oMariner 10 made 3 flybys of the plaet in 1974/1975 and photographed
45% of the planet’s surface
oThe Messenger mission made 3 flybys before entering in to orbit in March
2011
It was intentionally crashed in to Mercury on April 30, 2015
Each flyby also orbitied the sun (every 176 days) so its orbit aligned
with Mercury’s solar days, so it always looked the same
What did they find?
oMercury is very heavily cratered, much like the moon
oIt is a very ancient surface
oInstead of maria, Mercury has low lying lava plains
oMercury has “Scarps”
A scarp is a long, cliff-like feature
Thought to be formed by the cooling and cracking of the planet’s
surface
Shown because the angles of the scarps are consistent with
shrinkage
oThe “Caloris Basin”
A “bullseye” shaped impact crater with rings of mountain ranges
surrounding it
The hottest portion of Mercury when it is nearest the sun
On the opposite side of Mercury, there is hilly terrain, probably
formed when seismic waves from the impact that formed the basin
spread through the center of the planet
oWater on Mercury
Hidden in deep craters at the poles
oMagnetic field
Very weak- about 1% that of the Earth’s
It does have a working dynamo
Lots of iron! (it has a similar density to the Earth)
Weak because of the slow spin of the planet- it rotates once every
59 days
It is very variable
The center of the field is not in the center of the planet!!
oThe interior
Thought to have an immense iron core, and a very small mantle,
with a thick crust
oMANY questions remain
-The first mission to Venus and Mars demolished decades of speculations about those
planets
Venus
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