Transcript Understanding Orbits

The Terrestrial Planets
 Know about Mercury
 Know about Venus
 Know about Mars
The View of Mercury from Earth
• Because Mercury is closest to the Sun you can only
see it shortly before dawn or after dusk when the Sun
is below the horizon
Mercury’s Composition and Orbit
 Diameter - 3,033 miles
 Density - 5.43 times the density of
water (Why so dense?)
 Mercury circles the Sun quickly
(88 days)
 The planet rotates one and a half
times for every time it goes
around the Sun
Messenger Mission
• Messenger Spacecraft
• August 3, 2004 -- MESSENGER Launch
March 2011 -- Yearlong science orbit of
Mercury begins
The View of Venus from Earth
 The second closest planet to
the Sun
 Except for the Sun and Moon,
it’s the brightest object in the
sky
 It is visible only in the evening
after sunset and in the
morning sky before sunrise
Venus’s Composition and Orbit
 Venus is often called Earth’s sister
planet
 Diameter is 95 percent of Earth’s
 Mass is 82 percent of Earth’s
 Its orbit is located closest to the Earth
 Density: 5.24 times that of water
 Slow rotation (about 243 days)
 While all eight planets revolve
around the Sun in a
counterclockwise fashion, Venus
and Uranus are the only two that
rotate in a clockwise fashion
Venus’s Surface and Atmosphere
 All of Venus is drier than the
driest desert on Earth
 Venus has about a thousand
craters
 Venus has an atmosphere
made up of about 96 percent
carbon dioxide, 3.5 percent
nitrogen and small amounts
of water and sulfuric acid
The View of Mars From Earth
 The best time to look at Mars
is when it is in opposition—
when a planet is directly
opposite the Sun in the sky
 This occurs every 26 months
 Next period of opposition:
April 8th, 2014
 Mars is in opposition about
every 2.2 years
Mars’ Composition and Orbit
 Diameter about half of the
Earth’s
 Mass is only one-tenth that of
Earth
 Scientists calculate that Mars’
density is 3.93 times that of
water, about 0.7 of Earth’s
density
 Mars rotates almost as quickly
as Earth
Mars’ Orbit and Magnetic Field
 Orbits the Sun from about 143
million miles away
 Day is 24 hours and 40
minutes
 Mars doesn’t have a magnetic
field
 Mars probably lost its
magnetic field about 4 billion
years ago
Mars’ Surface and Atmosphere
Pioneer: May 2008
Rover 2004
http://www.nasa.gov/mission_pages/msl/index.html
The Terrestrial Planets
 Know about Mercury
 Know about Venus
 Know about Mars