Mercury
Note 16
History:
* Known (& recorded) at least since 3000
BC by Sumerians
* Greeks called it Apollo in the morning
& Hermes in the evening
* Renamed Mercury after the Greek god of
commerce, travel and thievery because it
moved so quickly across sky
* (& discovered to be only 1 planet)
* Can only be viewed at sunrise or sunset (&
also has phases like Venus & moon)
Mercury – best
known for his
speed
Basic Background:
* closest to sun (on avg 58 million km or
36 million miles)
* 8th largest (2nd smallest) with a diameter of
4854 km (3015 miles)
* it has a mass ~ 0.056 the mass of Earth
temp ranges from - 180° C to 430° C
* tilted about 5° off of the plane of the ecliptic
* Takes 88 days to revolve around sun
* One Mercurian day = 59 earth days
* No known satellites
Composition:
* surface is highly cratered from old
meteorites that still exist because it:
- has no water, atmosphere or
erosion to erase them
* Mariner 10 (unmanned probe in 1970’s)
discovered a magnetic field indicating an
iron core
* The largest known surface feature is the
Caloris Basin (1350 km across)
* Has huge cliffs some over 100 km long
Gravitational pull is about ¼ of gravity on
Earth
Who has been there?
So far, only Mariner 10 has gotten a look at
Mercury. It flew by Mercury on 3 occasions:
- March 29, 1974
- September 21, 1974
- March 16, 1975
What did it find?
- measured temperatures, gravity
- took over 3,500 photos
- confirmed that Mercury had no atmosphere
- showed the surface was a cratered dormant
Moon-like surface
- found Mercury to have a small magnetic
field and a relatively large iron-rich core
Next mission: Messenger
- launched on Aug 3, 2004
- will flyby a few times but should orbit
Mercury for a year in 2011
Goals of Mission:
- find out if pictures from craters really do
show ice
How could there be
ice if it is so hot?
- Mercury rotates
perpendicular to
axis so craters get
very little sun
(angles don't let sun
in)
Other goals:
- provide the first images of the entire planet.
- collect detailed information on:
- the composition and structure of
Mercury's crust
- its geologic history
- nature of its thin atmosphere
- makeup of its core and polar materials