Mercury

Astronomy 311Professor Lee

CarknerLecture 10

Why do we think the Earth’s core is made of iron?

a) Iron meteorites are the most commonb) Deep drilling rigs have brought up iron from

the corec) The Earth’s bulk density is much higher

than the density of rockd) The Moon is mostly made of iron and so the

Earth should be tooe) Spectroscopic analysis of volcanoes reveal

iron

How does the Earth cool off if it gets too hot?

a) Some of the hot upper atmosphere is lost into space

b) Greenhouse gases react with CO2 and are neutralized

c) The ice caps melt, cooling the oceansd) The greenhouse gases will dissolve in

water and rain out of the atmospheree) It won’t, once the atmosphere gets hot it stays

that way forever

Mercury -- Messenger of the Gods

Romans named it Mercury because it changes position in the sky so fast

Mercury is hard to see since it always appears near the Sun

Viewing Mercury From Earth

View Mercury with the naked eye in the morning or evening Mercury is always near the Sun

Very hard to see any surface features Mercury can sometimes be seen

passing in front of the Sun, called a solar transit When viewing Mercury, always be careful of

the Sun

Mercury Facts

Size: 1/3 size of Earth

Orbit: ~0.4 AU

Description: small, airless, cratered

Mariner 10

The first spacecraft to explore Mercury Visited both Venus and Mercury

Mariner 10

Surface of Mercury Mercury has very little atmosphere (trace amounts

of material blasted off the surface by the solar wind)

Newer craters on top of older

Radar studies indicate that the poles are more reflective than the rest of the planet Possibly due to water ice in crater shadows

Impacts

Impacts have been very common during the history of the solar system Earth’s weather tends to erase craters

Most occurred during Heavy Bombardment Period, about 3.8 billion years ago

Kinetic Energy What happens when two bodies

collide?

KE = 1/2 mv2

v is the velocity (in m/s)

a Watt is a joule per second

Caloris Basin

Caused by very large impactor

Not many craters on top of it, so it must be fairly young

Geological Map of Caloris Region

Spin-Orbit Coupling

The Sun pulls on this bulge slowing down the rotation of the planet (the spin)

Mercury has 3 to 2 spin orbit coupling

3 rotations on axis for every 2 orbits or 1.5 rotations per orbit

Mercury’s Spin-Orbit Coupling

Consequences of Spin Orbit Coupling

Mercury has long days and long nights

Day side gets hot, night side gets cold Day ~700 K, night ~100 K

Day and Night on Mercury

Sun

Sun

700 K(800 F)

100 K(-270 F)

Noon

Midnight (3 months later)

Brrr

Ouch!

Interior of Mercury Mercury has a very high density

Why is density so high? Possibly caused by a large impact stripping off

much of the lighter outer layers leaving a disproportionately large core

Why is core molten? Mercury is small, so core should have cooled

Inside Mercury

Future Mercury Exploration

The MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission

Will only start orbiting Mercury in 2011

Orbits Mercury for 1 year and will make detailed maps of the surface

Next Time

Read Chapter 9

Summary

Mariner 10 data reveals Mercury as a small, airless, heavily cratered world

Mercury exhibits 3 to 2 spin orbit coupling due to the Sun’s tidal force 1 1/2 rotations on axis per revolution

around the Sun Mercury has a high density, possibly

due to large iron core