Rotation
Rotation
Rotation
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The Planets<br />
***(But Not Earth)<br />
We already<br />
learned all<br />
about Earth….<br />
…right?
=> to scale…
Mercury - Greeks<br />
Venus - Greeks<br />
Mars - Greeks<br />
Jupiter - Greeks<br />
Saturn - Greeks<br />
Moons of Jupiter - 1609/1610 (Galileo)<br />
Saturn's rings - 1659<br />
Uranus - 1758<br />
Ceres (largest asteroid) - 1801<br />
Neptune - 1846<br />
Pluto - 1930
Terrestrial<br />
Planets
errestrial Planets include...
=> to scale…
You Need To Know...<br />
• <strong>Rotation</strong> - spinning on<br />
its axis<br />
• Revolution - orbit<br />
around Sun
How do we know if a<br />
planet rotates???<br />
Bounce<br />
radio<br />
waves<br />
off the<br />
planet
Remember:<br />
Red Shift -<br />
Blue Shift -<br />
Object moving<br />
away<br />
Object moving<br />
closer
Mercury<br />
“The Quick Planet”
god of<br />
commerce
• smallest terrestrial<br />
planet<br />
• only slightly bigger<br />
than our moon<br />
• density of ~ 5.5 g/cm 3<br />
• 0.39 AU from Sun<br />
• No moons
Mercury is very hard to<br />
observe since it is always<br />
so close to the Sun.<br />
We can only see it in<br />
morning or evening.
• Revolution Period - 88 days<br />
<strong>Rotation</strong> - once every 59 days<br />
Orbits 7º off the ecliptic plane
The Sun's gravity has altered Mercury's<br />
rotation so that it rotates exactly three<br />
times for every two revolutions it makes<br />
around the Sun. Like our own Moon<br />
spinning exactly once for each trip<br />
around Earth.<br />
3 rotations per 2 revolutions<br />
rotation period = 2/3 orbital period
• weak magnetic field due<br />
to slow rotation<br />
• atmosphere almost none<br />
(weak gravity and very hot)<br />
=> gasses escaped<br />
• abnormally large core<br />
Or thin mantle?
Why?<br />
1) too hot for lighter<br />
elements to collect<br />
2) very powerful solar<br />
wind blew mantle away
3) collision with large<br />
planetisimal knocked mantle<br />
away and added to the core
Temperature:<br />
ranges from 100 K (-280ºF)<br />
to 700 K (870ºF)<br />
from slow rotation and<br />
lack of atmosphere<br />
(largest range in solar system)
• rotational axis<br />
perpendicular to orbital<br />
plane So...<br />
Sun never hits poles,<br />
evidence of water ice there
1973 – Mariner 10 Satellite<br />
first pics of<br />
Mercury
2008 – MESSENGER<br />
August 3, 2004 -- MESSENGER Launch<br />
August 2005 -- Earth flyby<br />
October 2006 -- Venus flyby<br />
June 2007 -- Venus flyby<br />
January 2008 -- Mercury flyby<br />
October 2008 -- Mercury flyby<br />
September 2009 -- Mercury flyby<br />
March 2011 -- Yearlong science orbit of Mercury begins
Surface looks like our Moon’s<br />
• Has maria regions<br />
• Lots of<br />
craters
Except-<br />
Scarps - large cracks in<br />
the surface caused by<br />
interior rocks cooling<br />
and shrinking.
• Caloris basin - site of a<br />
huge impact!<br />
(1340 km crater)<br />
That’s 830 miles wide!!!<br />
• Weird terrain…
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