The Terrestrial Planets

Exploration of Mercury

Mercury Half-Mapped

Mercury’s Orbit• Fairly eccentric with e=0.21

– Perihelion distance = 0.31 AU– Aphelion distance = 0.47 AU

• Resonance

– So Mercury rotates 3 times for every 2 orbits around the Sun

– This is a tidal effect from the Sun

The Mercurian Day

Advance of Mercury’s Orbit

General Properties of Mercury

Temperature– 100 K at night to 700 K by day

Magnetic Field– Surprisingly strong at ~0.5% of Earth’s– Magnetic field and high average density

suggest a large iron coreAtmosphere

– NoneInterior

– Large iron core - 1/3 by volume, extending to about 70% of radius

Degas

Impact craterabout 45 km

wide

Imaged by theMariner 10

flybys

Surface Effects

Scarps are seen on Mercury.

Useful for relative dating and history of the

surface.

Caloris Basin

Interior of Mercury

Origin Model for Mercury