Mercury Mercurys Orbit Mercury has a short year

Mercury

Mercury’s Orbit • Mercury has a short year. – 88 Earth days = 1/4 Earth year – 0. 4 AU from the Sun • This is predictable from Kepler’s third law. – The period squared compared to the distance cubed – Period (0. 25) x (0. 25) = 0. 063 – Distance from Sun (0. 4) x (0. 4) = 0. 064

Tidal Lock • With the strong gravity from the nearby sun, Mercury should have tidal friction. – One side would always face the sun • Measurements with radio telescopes showed that Mercury rotates in 58. 7 days. • There is a lock, but Mercury takes three rotations every two revolutions of the sun.

Mercury’s Day and Year • The apparent day on Mercury is twice as long as the year. day 0 day 29 sun day 88 day 59 sun day 117 sun day 147 sun

Close Up • In 1974 -5 Mariner 10 flew by Mercury. – Measured surface – Still orbiting the Sun • In 2004 Messenger was launched. – Flyby in 2008 – Orbit since 2011

Solar Broil • Mercury is the closest planet to the sun (0. 4 AU). – Surface temperature reaches 700 K (870 ºF) – Poles at 100 K (-280 ºF) • There is water under the surface at the poles. • The atmosphere is mostly burned off. – Gravity too low – Traces of gas coming from the surface

Cratered Surface • Mercury is a terrestrial planet - it has a rocky surface. • The surface is heavily cratered like the moon, due to impact in the early solar system. • There are signs of lava flows and tectonics.

Albedo • Planets reflect the light of the sun. • The fraction of the light reflected compared to what falls is called albedo. • Mercury and the Moon both have low albedo (0. 06 -0. 07). • The dark cratered surface does not reflect well.

Mini Magnet • The mass of Mercury is 1/20 of Earth. – Almost equal density • The remaining rock is more iron rich than Earth. • Mercury has an iron core and weak magnetic field.