Chapter 12: Dwarf Planets and Small Solar System Bodies

Pluto: distant ice world that was once a planet

Pluto was discovered by Clyde Tombaugh in 1930 Percival Lowell made calculations on the orbit of Neptune and predicted a 9 th planet. His calculations were based on flawed data, there is no 9 th planet.

Pluto’s moon Charon was discovered by James Christy in 1978

Pluto and Charon are tidally locked on each other Just as we only see one side of our moon from Earth, Pluto only sees one side of Charon. Since Pluto is also tidally locked, Charon also only sees one side of Pluto.

Four more moons have been discovered around Pluto

Pluto, Charon, Nix and Hydra are not very large

Pluto Has An Atmosphere!

The New Horizons mission is on its way to Pluto. It will fly by in 2015

Eris is the reason Pluto isn’t a planet anymore

There are a number of “large” Kuiper Belt Objects

There are now 5 Dwarf Planets

Ceres has been promoted from asteroid to dwarf planet Ceres was called a planet when it was discovered in 1801 but it was later demoted when we started to find lots of other objects in the asteroid belt

The Debris of the Solar System Asteroids and comets are leftover planetesimals. We don’t see the icy planetesimals until the fall in to the inner part of the system solar

When a piece of an asteroid comes close to Earth it may become a meteor

Meteoroids, Meteors and Meteorites NEO 1994 XM 1 Leonid Meteor Shower

Big rocks DO fall from the sky! Fortunately for us, they don’t do it too often

A bad day for the dinosaurs

The impact released trillions of tons of CO 2 into the atmosphere The crater is buried several hundred meters under the surface and is over 200 km in diameter

Fortunately, most impacts are small The Peekskill meteorite fell in 1992 and hit an 1980 Chevy Malibu. Insurance wouldn’t pay for the damage but she got $10k for the car and $69k for the meteorite from a collector.

Meteorites are classified as Stones, Irons or Stony-irons

The most common meteorite, stones look like ordinary rocks with burnt crust

The most common “find” is an iron meteorite

Widmanstätten Patterns are iron crystals that take millions of years to form The iron has to cool from the molten state at no more than a few degrees every million years to form these crystal patterns

Stony-Irons are intermediate between stones and irons

Carbonaceous chondrites are from the earliest age of the solar system They show the original condensation grains from the solar nebula period when they formed

The different types of meteorites implies different types of parent asteroids Some asteroids have a lot of carbon materials. These are known as C-type asteroids

S-type and M-type asteroids are from differentiated bodies

To form S-type and M-type asteroids a larger body must be smashed to pieces

Most (but not all) asteroids orbit between Mars & Jupiter

The Apollo, Aten and Amor asteroids cross Earth’s orbit

Most asteroids are small and irregular shaped

Asteroids tumble Most have rotational periods of 9 to 10 hours

Some asteroids are piles of debris 253 Mathilde

We have landed on one asteroid: Eros

Comets are the debris of the Outer Solar System

Many comets come from the Kuiper Belt The Kuiper Belt is a thick donut shaped region extending from about 30 AU out to 50 AU. Pluto and Eris are the largest known Kuiper Belt objects

Some comets come from the Oort Cloud The Oort Cloud may extend out to a lightyear (50,000 AU) from the Sun

When a comet approaches the inner solar system the ice evaporates

The gas and flaked off dust form a coma and tail

A comets tail always points away from the Sun There are two tails: a dust tail that trails behind some and an ion tail that always points directly away from the Sun

Comet tails can be millions of kilometers long

The tail can break off due to “gusts” in the solar wind

Comet orbits are tilted from the ecliptic and very eccentric

What happens to comets?

Comets “die” in one of three ways 1: They fall in to the Sun They don’t have to actually fall into the Sun, just get close enough to burn up

2: They collide with a planet or moon Shoemaker-Levy 9 had a amazing collision with Jupiter in 1994

Will a comet ever hit us? The highest rated object is rated a little below 1

We were probably hit by a fragment of a comet in 1908 The Tunguska event flattened over 800 square miles of forest in Siberia. It was probably an object about the size of a football field that exploded about five miles above the surface

3: They break-up and fizzle out

Meteor Showers come at regular times of the year

Meteor Shows are the result of Earth passing through a debris trail left by a comet

Usually, meteor showers are a few dozen to a few hundred per hour

On rare occasions there are meteor storms The 1833 Leonid meteor storm

Most of the stuff floating around out there is dust sized Most of the dust is flaked off from comets and burns up in the atmosphere before reaching the ground

There is so much dust in the ecliptic we can see its glow It’s called the Zodiacal Light because it lies along the ecliptic which is the line of the zodiac