Mercury

1
Mercury

• The first planet we encountered heading out from
  the Sun is Mercury
• Mercury's proximity to the Sun leads to very
  harsh conditions for this small planet
• Most of the characteristics of Mercury we will
  discuss are a direct result of its nearness to
  the Sun

2
Properties of Mercury
3
Mercury's Interior

• _
• In order to have such high densities and a
  smaller size, Mercury must contain much more
  dense, heavy material
• Mercury's proximity to the Sun led to a
  composition of mostly heavy metals, mainly iron

Mercury is believed to have a very large iron
rich core.
4
Mercury's Surface

• Mercury's surface was imaged by the Mariner 10
  spacecraft in 1974/75
• _
• Mariner 10 did not orbit Mercury, but instead
  completed multiple 'fly-by' maneuvers
• To date, only about 48 of Mercury's surface has
  been imaged

Area not imaged
5
Cratering

• Like all the planets, Mercury was bombarded by
  meteors early in its life
• Relatively little or no surface activity has left
  these scars untouched on the surface for billions
  of years
• _
• The impact sent shockwaves through the planet,
  rippling the surface directly opposite the crater

6
Mercury's Scarps

• Many of the close up images of Mercury's surface
  show ridges or cliffs called scarps
• _
• As the interior of Mercury cooled, it shrank,
  causing the surface to wrinkle
• Similar to a grape becoming a raisin

7
Mercury's Atmosphere?

• _
• The smaller the planet (or moon), the harder it
  is to retain an atmosphere
• A planet's gravity traps gas to form an
  atmosphere
• Less mass means less gravity
• There is some evidence for Mercury temporarily
  capturing solar wind, but it is never permanently
  retained
• Without an atmosphere, the temperature extremes
  on Mercury are huge
• 100 K on the night side, 700 K on the day side

8
Observing Mercury

• _
• Due to its close orbit to the Sun, Mercury is
  only visible shortly after sunset or shortly
  before sunrise
• In addition, Mercury can never get more than 28o
  away from the Sun in the sky, making it quite
  hard to see

9
Mercury's Rotation

• Early astronomers attempted to measure the
  rotation of Mercury by watching features on its
  surface move
• _
• For many decades, it was believed that Mercury's
  rotation was equal to it revolution of the Sun
  (just like the Moon around the Earth)

Image of Mercury taken from one of the largest
telescopes on Earth.
10
Mercury's Rotation

• In 1965, astronomers at the Arecibo radio
  telescope bounced radar signals off of Mercury's
  surface to measure its rotation
• When the signal hits Mercury's surface, one side
  of the planet will be moving toward Earth, the
  other moving away
• This causes the light to become Doppler shifted
• The size of the shift can be used to calculate
  the rotation speed

Blueshift
Redshift
11
Mercury's Rotation

• _
• Instead, one rotation of Mercury takes about 58.6
  days, while a revolution around the Sun takes 88
  days
• This relationship is called a 32 resonance (3/2
  X 58.6 days 88 days)

12
Visiting Mercury

• So far, the only space probe to visit Mercury was
  Mariner 10
• The MESSENGER probe will be the next explorer of
  Mercury
• _
• After making a few fly-bys of Mercury, it will
  orbit the planet in 2011

13
Obtaining an Orbit
MESSENGER Orbit Movie