Pluto, Comets, and Space Debris

Chapter 8

Topics

• What is Pluto?

• Trans-Neptunian Objects (Kuiper Belt)

• Asteroid Belt

• Meteroids, meteors, and meteorites

• Near-Earth Objects

Pluto

• Discovered in 1930• Orbit is highly elongated

compared to other planets.• Orbital plane is tilted with

respect to the ecliptic.• It has a moon - Charon

(discovered in 1978)• Difficult to “see”• No spacecraft have visited

Pluto• Was thought to affect

Uranus’ orbit

View of Pluto and Charon as distinct objects for the first time (HST 1990)

Finding Pluto

Practice

• How do we know the mass of Pluto?• Its density is 2 g/cm3. What do you think

it’s made of?• It’s similar to the moons of the Jovian

planets. Why is it most likely not a “lost moon” of one of the Jovian planets?

• If there’s one object like Pluto, could there be more?

Kuiper Belt

• 1950s: Gerard Kuiper suggested that Pluto formed as part of a larger group of comet-like objects, which should still be there.

• 1980s: Theorists predicted 200 million objects between 34 and 50 AU.

1993 SC

• One of brightest known Kuiper objects.

• currently 34.0 AU from the sun but may travel as far as 48 AU.

• Diameter is around 300 km, or just a quarter the size of Pluto's moon Charon.

• hundreds of known TNOs ( see the KBO home page.)

So what is Pluto?

• Whether Pluto is classified as a planet or some other type of object depends on what other Kuiper-belt objects (or Trans-Neptunian Objects) we find. If more are found that are similar in size or larger than Pluto, then Pluto will likely be declassified as a planet.

• Pluto is professionally classified as a TNO although popularly classified as a planet.

Comets

• Two types:– SHORT PERIOD: return

regularly on time scales of hundreds of years--Halley’s Comet

– LONG PERIOD: return with periods of hundreds to millions of years

• the average semimajor axis is about 50,000 AU

• aphelion distances are about 100,000 AU

• orbits are highly eliptical• not all orbits are closed orbits

6 ly

Oort Cloud (proposed in 1950)

50,000-190,000 AU

Hale-Bopp

Comet structure• TAIL: dust and gas--nearly 1 AU!!• COMA: head of the comet, ~10

times size of Earth--still very low density

• NUCLEUS: center of head, block of ice and gas, “dirty snowball”--about 10 km across

• Tails are caused by gas jets resulting from the vaporization of ice as the comet nears the Sun.

• Not all comets have tails, even when they are near the Sun; no comets have tails when they are far from the Sun.

• Many comets break up due to tidal forces as they near the Sun.

animation

Comet tails

• How do we know that one tail is gas and the other tail is dust?

Fate of comets

1. dissipates or breaks up as it nears the Sun.

2. collides with a planet

3. a close encounter with a planet alters its orbit so that it leaves the Solar System

So what does this tell you about the age of the periodic comets and the origin of comets?

Shoemaker-Levy 9

Asteroids

• irregular rocky matter• referred to as minor planets• Ceres, the largest known

asteroid is about 1/3 the size of the Moon and 1/100 its mass

• Most orbit the Sun in a belt between Mars and Jupiter

• ~5500 discovered so far• irregular surfaces and shapes

Gaspara

NEAR Shoemaker

• Near Earth Asteroid Rendevous mission

• NASA web site• Orbited EROS starting

Feb. 14, 2000• Landed on EROS Feb.

12, 2001• Eros is classified as a

Near Earth Object

Near Earth Objects

Some asteroids come within 1.3 A. U. of the Earth and cross the Earth’s orbit

Collisions with these asteroids are likely the result of the large impact craters on Earth and likely impacted life on Earth in the past

Moons of Mars

• Deimos and Phobos• most likely are

captured asteroids• “lumpy” shapes

Practice

• When sending spacecraft to the Jovian planets, how likely is it that the spacecraft will collide with an asteroid when passing through the asteroid belt?

Meteors

• meteoroids, usually very small, sometimes as large as a meter enter the Earth’s atmosphere.

• the streak of light due to the burning meteoroid is called a meteor or shooting star

• the remains, if there are any, that hit Earth are called meteorites– sometimes metallic, sometimes rock, sometimes a

combination– oldest meteorites are about 4.6 Gy– give clues to the formation of the Solar System

Meteor showers

• normal rate: few per hour

• meteor shower: >50 per hour

• trails of space debris left by comets

• When should you look?

Leonids

• Predictions; NASALeonid meteor storms happen when Earth plows through clouds of dusty

debris shed by comet 55/P Tempel-Tuttle. Right now Earth is heading for two such clouds. "We'll collide with both of them on Tuesday morning, Nov. 19th," says Cooke. "The first cloud will cause a flurry of meteors over Europe at about 0400 UT. We expect sky watchers in the countryside (away from bright city lights) to see between 500 and 1000 Leonids per hour.”

Earth will plow into the second cloud about six hours later (1030 UT or 5:30 a.m. EST) and cause an even bigger outburst over North America. "Observers here in the United States could see as many as 2000 per hour," he predicts.

Bring a food, a friend, a blanket and stay awhile

Quadrantids Jan. 1-5

Lyrids April 16-25

Eta Aquarids April 19 - May 28

Delta Aquarids July 8 - Aug. 19

Perseids July 17 - Aug. 24

Orionids Oct. 2 - Nov. 7

Leonids Nov. 14-21

Geminids Dec. 7 - 17