Mercury Astronomy 311 Professor Lee Carkner Lecture 10

Mercury -- Messenger of the Gods  Closest planet to the Sun, shortest orbital period   Mercury is hard to see since it always appears near the Sun

Mercury From Earth

Solar Transit of Mercury

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    When viewing Mercury, always be careful of the Sun

Mercury Facts  Size: 1/3 size of Earth   Orbit: ~0.4 AU   Description:

Mariner 10  The only spacecraft to explore Mercury    Did not image all of Mercury (only about 45%)

Mariner 10

Surface of Mercury   Heavily cratered   Scarps or cliffs indicate that Mercury shrank as it cooled  Radar studies indicate that the poles are more reflective than the rest of the planet 

Impacts   Impacts have been very common during the history of the solar system  

Kinetic Energy  What happens when two bodies collide?   KE = 1/2 mv 2     a Watt is a joule per second

Caloris Basin  Large (1300 km) crater    Not many craters on top of it, so it must be fairly young

Geological Map of Caloris Region

Spin-Orbit Coupling  The Sun’s gravity produces a tidal bulge, elongating Mercury   The spin wants to slow down to match the period of the orbit  Mercury has 3 to 2 spin orbit coupling   3 rotations on axis for every 2 orbits 

Mercury’s Spin-Orbit Coupling

Consequences of Spin Orbit Coupling  Mercury takes 59 days to complete one rotation  Mercury has long days and long nights    Day ~700 K, night ~100 K

Day and Night on Mercury 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?  Answer: Large iron core   Mercury has a small magnetic field, so core must be molten to generate it via the dynamo effect 

Inside Mercury

Future Mercury Exploration  The MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission  Launched August 3, 2004   Orbits Mercury for 1 year and will make detailed maps of the surface 

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