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

• Volcanoes erupt constantly on Io’s surface.– Sulfur spews out

from the surface.

– Low escape velocity means that the sulfur escapes.

• 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.

Io

• 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.

Europa

• 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.

Saturn’s Moon Titan

• 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.

Neptune’s Moon Triton

• 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.

Pluto and its Moons

• 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

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

• The head consists of– The nucleus, a lump

of frozen gas mixed with loose rock and dust.

• Only about 10 km across.

• 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.

The Structure of Comets

Comet Halley, visited by Giotto

Comet Wild 2, visited by Stardust

Comet Tempel 1, visited by Deep Impact

Visiting 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.

The Origin of Comets

• 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).

How a comet becomes visible

Another View of the Process

• 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.

Meteor Showers

• 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 Moon Phase

Quadrantids January 3, 4 First quarter

Lyrids April 21/22 First quarter

Aquarids May 5, 6 Third quarter

Perseids August 12, 13 New Moon

OrionidsOctober 21, 22 Near full

Leonids November 17/18 Near full

Geminids December 13/14 First quarter

• Meteors can leave a trail of glowing gas from their passage

• Large meteors (> 4 cm or so) are called fireballs

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.

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:

• 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.

2

2

1VmEK

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

The Asteroid Belt

• 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.

• 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.

The Shapes and Sizes of Asteroids

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