This set of slides

.

• This material finishes up our brief tour of the solar system: trans-neptunian objects, comets, meteors, meteorite impacts, and asteroids.

• Units covered: 46, 47, 48, 41

Io • Io is closest to Jupiter.

• Io has a very active interior.

– Experiences tidal forces from Jupiter and gravitational tugs from Europa, squeezing it.

– Similar to bending a metal clothes hanger back and forth until it heats up.

• Volcanoes erupt constantly on Io’s surface.

– Sulfur spews out from the surface.

– Low escape velocity means that the sulfur escapes.

Europa • Europa is covered with cracks in its surface.

– Red, mineral-rich water seeps out to make the crack visible.

• Very few craters.

• Metallic core, surrounded by a thick rocky layer.

• Weak magnetic field.

• Heat from the interior is likely enough to keep a liquid ocean of water beneath its icy crust.

Saturn’s Moon Titan

• Titan is Saturn’s largest moon

– Larger than Mercury.

– Thick atmosphere of nitrogen (which gives it the orange color.) – Temperature of 95K – Atmospheric pressure similar to Earth –

Huygens

probe sent back pictures of what looks like rivers and lakes of methane .

Neptune’s Moon Triton • Triton is larger than Pluto and almost as big as Europa.

• Orbits backwards relative to Neptune’s rotation.

– Likely a captured icy planetesimal.

• Has an atmosphere that freezes out on the night side of the planet.

• Odd surface features.

Pluto and its Moons • Pluto is the only planet in the solar system that we have not visited.

• Pluto and its largest moon Charon would fit comfortably within the United States.

• Charon orbits Pluto at a steep angle to the ecliptic, and Pluto’s axis is heavily tipped as well.

• Two new moons were discovered in 2005, and were named Nix and Hydra in 2006.

• Pluto is a mix of water ice, rock, methane and frozen nitrogen.

• When Pluto is within Neptune’s orbit, it has an atmosphere.

– As the planet moves further out in to the solar system, the atmosphere snows out onto the surface.

• • More than 130 have been discovered, one of them larger than Pluto.

Plutinos

are bodies that orbit the Sun at more or less the same distance as Pluto.

• Small icy bodies orbiting the Sun beyond Neptune’s orbit are called

Trans Neptunian Objects

, or TNOs.

Trans-Neptunian Objects

The Structure of Comets • • Comets have two primary parts, the head and the tail.

The head consists of – The dust.

nucleus

across.

, a lump of frozen gas mixed with loose rock and • Only about 10 km • Dark in color, probably from dust and other materials.

– The

coma

, the cloud of evaporated ices and gases streaming from the surface of the nucleus.

• May be 100,000 km wide.

• The tail can be hundreds of millions of km long, and streams directly away from the Sun.

Comet Halley, visited by

Giotto

Visiting Comets Comet Tempel 1, visited by

Deep Impact

Comet Wild 2, visited by

Stardust

The Origin of Comets • Comets may originate in either the

Oort Cloud

or the

Kuiper Belt.

– Oort cloud is a cloud of comet-like planetesimals more than 100,000 AU from the Sun.

– Oort cloud objects may have formed near the giant planets and then were tossed outwards by gravitational forces.

• Passing stars or other gravitational influences nudge the comets into the inner Solar System.

How a comet becomes visible • As a comet moves into the inner solar system, it is warmed by the sun.

– Ices on the surface

sublimate

(go from solid to gas) and stream away from the comet nucleus.

– The sublimated gases form the coma.

– Escaping gas carries dust particles outward.

• Solar photons strike the dust particles, pushing them away – Process is called

radiation pressure.

– This forms the dust tail.

• Gas and ions in the coma are pushed away from the nucleus by the

solar wind.

– This forms the ion tail, and usually points directly away from the Sun.

• Gas in the coma and tail are lit up by the Sun, making them visible (fluorescence).

Another View of the Process

Meteor Showers • As a comet orbits the sun, it leaves a trail of dust behind it.

• Occasionally, the Earth passes through one of these dust trails – Dust particles enter Earth’s atmosphere and burn up – We see them as

meteors

, in a

meteor shower

• The meteors all appear to be coming from the same point in the sky called the

radiant.

• We name meteor showers after the constellation the radiant is located in.

• Perseus – Perseids • Leo Leonids and so on

The Names of Meteor Showers

2010 Meteor Showers

Name Date of Peak Quadrantids January 3, 4 Lyrids April 21/22 Aquarids

Perseids

May 5, 6

August 12, 13

Orionids October 21, 22

Leonids November 17/18 Geminids December 13/14

Moon Phase First quarter First quarter Third quarter

New Moon

Near full Near full

First quarter

The Heating of Meteors • When a

meteoroid

(small chunk of rock in space) enters the Earth’s atmosphere, it heats up and begins to glow.

– It is now called a

meteor.

• Meteors can leave a trail of glowing gas from their passage • Large meteors (> 4 cm or so) are called

fireballs

Meteorites • Most meteors burn up in the atmosphere.

• Some of them survive all the way to the ground, hitting the surface.

– These are called

meteorites

.

• Three kinds of meteorites: – Iron meteorites: made of iron, probably came from the cores of differentiated asteroids – Stony meteorites: Made of silicates, probably from the outer layers of asteroids – Stony-iron meteorites: a mixture of the previous two • Some stony meteorites look like loose material fused together – These are called

chondrites

– The clumps are called

chondrules

– Sometimes the chondrules are embedded in a sooty, carbon rich material (

carbonaceous chondrites

)

• Every so often, a large meteoroid (>10 meter) will strike a planet.

• Energy released by the impact is:

E K

 1 2

m



V

2 • Here, m is the mass of the meteoroid, and V is its velocity on impact.

• For a 100 kg meteoroid traveling at 30 km/s, the energy released is equivalent to 10 megatons of dynamite!

• And this was a small meteoroid. The Energy of Impacts

• Giant meteor craters can be found on Earth.

• Barringer Crater (left) in Arizona.

– Meteor was 50 meters in diameter – Crater is a mile across!

• Manicouagan Crater (right) – Meteor was 5 km in diameter – Crater is 73 km across!

Giant Meteor Craters

• About 65 million years ago, a 10 km wide meteoroid struck the Yucatan Peninsula • This impact caused massive climate changes, leading to the extinction of the dinosaurs and other forms of life • Iridium found in a layer of soil all over the world is the “smoking gun” Mass Extinction Events

The Chicxulub Crater

• Using

Bode’s Rule

(a simple mathematical formula that seemed to predict where planets would be found), the asteroid Ceres was discovered between the orbits of Jupiter and Mars.

• Soon many more small bodies were discovered.

• Now we know of 21,785 asteroids, located in the asteroid belt.

• The asteroids are not the remains of a shattered planet – All the asteroids mass added together is ~1% of the Earth’s mass.

The Asteroid Belt

The Shapes and Sizes of Asteroids • Asteroids come in all shapes and sizes – Ceres is the largest, only 930 km across – Ceres is massive enough to pull itself into a sphere – Most asteroids are not massive enough – Eros is potato shaped • Spacecraft have only recently visited asteroids – NEAR landed on Eros – Discovered craters and a regolith-covered surface • Most asteroids are very small 10’s of km across • Would still cause tremendous damage if one impacted Earth.

Origin of Asteroids • Asteroids are probably fragments of planetesimals.

• The planetesimal had collected a mixture of rock and metals, and then differentiated, creating a dense metallic core and a lighter, silicate-rich outer shell.

• A collision with another asteroid could have shattered the planetesimal.

– Fragments of the inner core would form the iron-nickel asteroids.

– Fragments of the outer shell would form the silicate asteroids