1. The Planets

2. Mercury Very similar to Earth’s moon in several ways:
Small; no atmosphere
lowlands flooded by ancient lava flows
heavily cratered surfaces
Most of our knowledge based on measurements by Mariner 10 spacecraft ( )
View from Earth

3. The Interior of Mercury
Large, metallic core.
Over 60% denser than Earth’s moon
Magnetic field only ~ 0.5 % of Earth’s magnetic field.
Difficult to explain at present:
Liquid metallic core should produce larger magnetic field.
Solid core should produce weaker field.

4. Venus and Mars Two most similar planets to Earth:
Similar in size and mass
Atmosphere
Same part of the solar system
Similar interior structure
Yet, no life possible on either one of them.

5. The Surface of Venus
Early radar images already revealed mountains, plains, craters.
Venus is made up of a lot of carbon dioxide. This gas traps heat from the sun and since Venus is so close to the sun, this causes Venus to be incredibly HOT!
Venera 13 photograph of surface of Venus:
Venus’ atmosphere has thick clouds.
Venus rotates backwards from all the other planets.

6. Craters on Venus Nearly 1000 impact craters on Venus’s surface:
 Surface not very old.
No water on the surface; thick, dense atmosphere
 No erosion
 Craters appear sharp and fresh

7. Mars Diameter ≈ 1/2 Earth’s diameter Very thin atmosphere, mostly CO2
Rotation period = 24 h, 40 min.
Axis tilted against orbital plane by 25o, similar to Earth’s inclination (23.5o)
Seasons similar to Earth
Due to the axial tilt similar to that of Earth.  Growth and shrinking of polar ice cap
Crust not broken into tectonic plates
Volcanic activity (including highest volcano in the solar system)

8. Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Galileo
Jupiter
Largest and most massive planet in the solar system:
Contains almost 3/4 of all planetary matter in the solar system.
Most striking features visible from Earth: Multi-colored cloud belts
Explored in detail by several space probes:
Visual image
Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Galileo
Infrared false-color image

9. Jupiter’s Rotation
Jupiter is the most rapidly rotating planet in the solar system:
Rotation period slightly less than 10 hr.
Centrifugal forces stretch Jupiter into a markedly oblate shape.

10. Saturn Mass: ~ 1/3 of mass of Jupiter
Radius: ~ 16 % smaller than Jupiter
Av. density: 0.69 g/cm3  Would float in water!
Rotates about as fast as Jupiter, but is twice as oblate  No large core of heavy elements.
Mostly hydrogen and helium; liquid hydrogen core.
Saturn radiates ~ 1.8 times the energy received from the sun.
Probably heated by liquid helium droplets falling towards center.

11. Rings are composed of ice particles
Composition of Saturn’s Rings
Rings are composed of ice particles
moving at large velocities around Saturn, but small relative velocities (all moving in the same direction).

12. The Atmosphere of Uranus
Like other gas giants: No surface. Rotates on its side.
Gradual transition from gas phase to fluid interior.
Mostly H; 15 % He, a few % Methane, ammonia and water vapor.
Optical view from Earth: Blue color due to methane, absorbing longer wavelengths
Cloud structures only visible after artificial computer enhancement of optical images taken from Voyager spacecraft.

13. Ices of water, methane, and ammonia, mixed with hydrogen and silicates
The Interior of Uranus
Average density ≈ 1.29 g/cm3  larger portion of rock and ice than Jupiter and Saturn.
Ices of water, methane, and ammonia, mixed with hydrogen and silicates

14. Neptune
Discovered in 1846 at position predicted from gravitational disturbances on Uranus’s orbit by J. C. Adams and U. J. Leverrier.
Blue-green color from methane in the atmosphere
4 times Earth’s diameter; 4 % smaller than Uranus

15. The Moons of Neptune Unusual orbits:
Two moons (Triton and Nereid) visible from Earth; 6 more discovered by Voyager 2
Triton: Only satellite in the solar system orbiting clockwise, i.e. “backward”.
Nereid: Highly eccentric orbit; very long orbital period (359.4 d).

16. Pluto as a Planet
Virtually no surface features visible from Earth.
~ 65 % of size of Earth’s Moon.
Highly elliptical orbit; coming occasionally closer to the sun than Neptune.
Orbit highly inclined (17o) against other planets’ orbits
 Neptune and Pluto will never collide.
Surface covered with nitrogen ice; traces of frozen methane and carbon monoxide.
Daytime temperature (50 K) enough to vaporize some N and CO to form a very tenuous atmosphere.

17. Meteorites Distinguish between: Meteoroid = small body in space
Meteor = meteoroid colliding with Earth and producing a visible light trace in the sky
Meteorite = meteor that survives the plunge through the atmosphere to strike the ground...
Sizes from microscopic dust to a few centimeters.
About 2 meteorites large enough to produce visible impacts strike the Earth every day.
Statistically, one meteorite is expected to strike a building somewhere on Earth every 16 months.
Typically impact onto the atmosphere with 10 – 30 km/s (≈ 30 times faster than a rifle bullet). .

18. Famous example: Barringer Crater near Flagstaff, AZ:
Meteorite Impacts on Earth
Over 150 impact craters found on Earth.
Famous example: Barringer Crater near Flagstaff, AZ:
Formed ~ 50,000 years ago by a meteorite of ~ 80 – 100 m diameter

19. Much larger impact features exist on Earth:
Impact Craters on Earth
Barringer Crater: ~ 1.2 km diameter; 200 m deep
Much larger impact features exist on Earth:
Impact of a large body formed a crater ~ 180 – 300 km in diameter in the Yucatán peninsula, ~ 65 million years ago.
Drastic influence on climate on Earth; possibly responsible for extinction of dinosaurs.

20. Analysis of Meteorites
3 broad categories:
Iron meteorites
Stony meteorites
Stony-Iron meteorites

21. Sizes and shapes of the largest asteroids, compared to the moon
The Asteroid Belt
Small, irregular objects, mostly in the apparent gap between the orbits of Mars and Jupiter.
Thousands of asteroids with accurately determined orbits known today.
Sizes and shapes of the largest asteroids, compared to the moon

22. Densities of comet nuclei: ~ 0.1 – 0.25 g/cm3
The Geology of Comet Nuclei
Comet nuclei contain ices of water, carbon dioxide, methane, ammonia, etc.:
Materials that should have condensed from the outer solar nebula.
Those compounds sublime (transition from solid directly to gas phase) as comets approach the sun.
Densities of comet nuclei: ~ 0.1 – 0.25 g/cm3
Not solid ice balls, but fluffy material with significant amounts of empty space.