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)
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.
• 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
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.
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:
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 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.
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.
• Only 2x as big as its moon (Charon)
• Since 1999, furthest “planet” from Sun
• Highly tilted orbit around Sun
Pluto Facts
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.