Week 4

Comets, Meteors, and Asteroids

The Demise of Pluto as a Planet

Extra-solar Planets

Reading: Chapter 4.1, 4.2, 8.5, 8.6, 4.4 (~24 pages)

TPS Question

How many planets are there?

a) 9

b) 8

c) 12

d) countless

Kepler’s Laws

• Orbits are elliptical.

• The closer an object is in its orbit to the Sun, the faster it goes.

• The square of the orbital period is proportional to the cube of its semi-major axis: P2 = a3. (P is how long it takes to make one orbit in years. a is distance in AU)

An Inventory of the Solar SystemEarly astronomers knew Moon, stars, Mercury, Venus, Mars, Jupiter, Saturn, comets, and meteors

Now known: Solar system has 135 moons, one star, eight planets (added Uranus, and Neptune), asteroids, and meteoroids

Terrestrial vs. Jovian Planets

Inner 4 planets (terrestrial) – small and rocky

Next 4 planets (Jovian) – gas giants

The big planets are what you think about when you think about the Solar System. But, in reality, there is much more to our Solar System than the planets.

Asteroids

Chunks of rock and metal left over from the formation of the solar system

Most asteroids very small (< 1 km).

Four are larger than 300 km (Ceres, Pallas, Juno, Vesta).

Most asteroids “live” in the asteroid belt – a region between Mars and Jupiter (2 to 3.5 AU).

• Probably not a destroyed planet.

• More likely a “failed” planet.

• Gravitational resonances from Jupiter would keep a planet from forming.

• Even so, it would only be ½ the size of the Moon.

The Asteroid Belt

Also Important: The Kuiper Belt• Flattened disk of solar system remnants out past Pluto

• The Solar System extends well beyond Pluto

Asteroids are found by looking for moving objects in still pictures

Over 10,000 asteroids have been cataloged by the “Minor Planet Center”

90,000+ await confirmation

There may be a billion or more asteroids

All the asteroids combined would still be smaller than Pluto

Asteroids are separated by millions of kilometers – nothing like the video game!

Asteroids

The inner solar system, showing the asteroid belt, earth-crossing asteroids, and Trojan asteroids

Asteroids

The inner solar system, showing the asteroid belt, earth-crossing asteroids, and Trojan asteroids

Earth-crossing AsteroidsSome asteroids have irregular orbits that take them across the path of Earth’s orbit.

Killer Asteroids

TPS Question

What is this?

a) Asteroidb) Meteoroidc) Meteord) Meteorite

Asteroids vs. MeteoriodsAsteroids and meteoroids have rocky composition; asteroids are bigger

(above) Asteroid Ida with its moon, Dactyl

(below) Asteroid Gaspra

(above) Asteroid Mathilde

Asteroids

Asteroids are large chunks of rock and metal left over from the formation of the solar system.

There is no established difference in size between meteoroids and asteroids.

Meteoroids

• Meteoroids are small asteroids

• They are up to a few meters in diameter

• Most are less than 1 millimeter

Meteor vs. Meteoriod vs. Meteorite

Meteoroid: A small rocky object orbiting the Sun

Meteor: The streak seen in the sky that is caused by a meteoroid burning up in the Earth’s atmosphere

Meteorite: Any piece of a meteoroid or asteroid that makes it through the Earth’s atmosphere and hits the Earth.

MeteorsMeteors are the flash that you see when a meteoroid hits the Earth’s atmosphere and gets burned up.

Meteorites

Meteorites are pieces of meteoroids that make it through the Earth’s atmosphere without burning up.

CratersThe impact of a large meteor can create a significant crater.

The Barringer meteor crater in Arizona:

The Tunguska EventFor example: An asteroid hit Siberia in 1908 and leveled a forest of trees.

What Killed the Dinosaurs?

The larger an impact is, the less often we expect it to occur

The dinosaurs may have been killed by the impact of a large meteor or small asteroid

The Universe Movie:The End of the Earth: Deep Space Threats to Our Planet(Just the first 20 minutes [first 3 chapters]).

Comets

“Dirty snowballs” – ice and rock mixed together

Comets From the Past

Comet West

Comet Kohoutek

Comet Hale-Bopp

Comet Hyakutake

CometsComets are icy, with some rocky parts.

The basic components of a comet:

Nucleus – about 10 km in diameter

Comet Nuclear Structure

Coma – halo of vaporized material from nucleus

Tails – are caused by the solar wind

Comets have 2 tails – the ion tail and the dust tail.

They can be as long as 1 AU.

Comet tails point away from the Sun

The dust tail is also influenced by the comet’s motion and tends to lag behind, making a curved tail

The ion tail points is caused by very light ions stripped away from the nucleus by the solar wind. Points directly away from the Sun.

The dust tail is made up of heavier dust particles, so it points partly towards the direction that the comet is coming from (but still away from the Sun).

There are 2 primary reservoirs of comets:

• The Kuiper Belt

• The Oort Cloud

Where Do Comets Come From?

Comet OriginsThe size, shape, and orientation of cometary orbits depend on their location. Oort cloud comets rarely enter the inner solar system.

Kuiper Belt

The Kuiper Belt• Flattened disk of solar system remnants out past Pluto

• Could be as many as 200 million comets here

The Oort CloudSpherical distribution of material even farther from the Sun than Kuiper Belt

~50,000 AU away

Comets here mostly in circular orbit unless they get disturbed, then they can enter the inner solar system

TPS Question

The yearly Geminid meteor shower is caused by

a) A meteroiodb) A meteorc) A cometd) An asteriod

Meteor ShowersMeteor showers occur when the Earth crosses the path of the orbit of a comet. Debris from the comet causes a shower of meteors.

These happen the same time each year.

They are named after the constellation that they appear to originate from.

Meteor Shower Dates

Meteors

What is the difference between a(n)

1) Meteor

2) Meteoroid

3) Asteroid

4) Meteorite

5) Meteor showers

OK, so there’s a lot of other stuff in the Solar System in addition to planets. This is where the topic of Pluto comes in.

Let’s look at why Pluto was demoted.

Our Nine Eight Planets

• Only 2x as big as its moon (Charon)

• Since 1999, furthest “planet” from Sun

• Highly tilted orbit around Sun

Pluto Facts

All orbits but Pluto’s and Mercury’s are close to the same plane

Is Pluto a Planet?

If Pluto is a planet, why not 2003 UB313 (Eris)?

“Dwarf Planets”: Ceres, Eris, and Pluto

Old Vs. New Solar System

Michael Brown

TPS Question

How many planets are there?

a) 9

b) 8

c) 12

d) countless

If Pluto isn’t a planet, then what’s this I hear in the news about all these new planets being discovered?

Extra-Solar Planets

That is, planets outside of our solar system.

Many planets have been discovered in other solar systems. Currently over 175.

This is one of the few that is visible.

Extra-Solar PlanetsMost extra-solar planets are discovered through the “wobble” they create in their parent star’s orbit.

Extra-Solar Planets, contOthers are discovered through the periodic dimming of the parent star’s luminosity.

Extra-Solar Planet Orbits/MassesThese are the orbits of most extrasolar planets discovered so far. All have masses closer to that of Jupiter than that of the Earth.

Extra-solar Planets Orbits/Masses

Trojan Asteroids

Trojan asteroids orbit in front of and behind Jupiter.

Caused by a gravitational resonance.

About 500 are known.