Transcript Mercury - NICADD

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) 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
sun
day 147
sun
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.