Week 4

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?
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
An Inventory of the Solar System
Early astronomers knew Moon, stars, Mercury,
Venus, Mars, Jupiter, Saturn, comets, and
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.
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).
The Asteroid Belt
• 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.
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
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!
The inner solar
system, showing
the asteroid belt,
asteroids, and
Trojan asteroids
The inner solar
system, showing
the asteroid belt,
asteroids, and
Trojan asteroids
Earth-crossing Asteroids
Some asteroids have irregular orbits that
take them across the path of Earth’s orbit.
Killer Asteroids
TPS Question
What is this?
Asteroids vs. Meteoriods
Asteroids and meteoroids have rocky composition;
asteroids are bigger
(above) Asteroid
Ida with its
moon, Dactyl
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
• 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
Meteorite: Any piece of a meteoroid or asteroid
that makes it through the Earth’s atmosphere and
hits the Earth.
Meteors are the flash that you see when a meteoroid
hits the Earth’s atmosphere and gets burned up.
Meteorites are pieces of meteoroids
that make it through the Earth’s
atmosphere without burning up.
The impact of a large meteor can create a
significant crater.
The Barringer meteor crater in Arizona:
The Tunguska Event
For example: An asteroid hit Siberia in
1908 and leveled a forest of trees.
What Killed the Dinosaurs?
The dinosaurs
may have been
killed by the
impact of a
large meteor or
small asteroid
The larger an
impact is, the
less often we
expect it to
The Universe Movie:
The End of the Earth: Deep Space Threats to Our Planet
(Just the first 20 minutes [first 3 chapters]).
“Dirty snowballs” – ice and rock mixed together
Comets From the Past
Comet Hyakutake
Comet West
Comet Kohoutek
Comet Hale-Bopp
Comets 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
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).
Where Do Comets Come From?
There are 2 primary reservoirs of comets:
• The Kuiper Belt
• The Oort Cloud
Comet Origins
The 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 Cloud
Spherical 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
TPS Question
The yearly Geminid meteor
shower is caused by
A meteroiod
A meteor
A comet
An asteriod
Meteor Showers
Meteor 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
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
Our Nine Eight Planets
Pluto Facts
• Only 2x as big as its moon (Charon)
• Since 1999, furthest “planet” from Sun
• Highly tilted orbit around Sun
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?
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
Many planets have
been discovered in
other solar systems.
Currently over 175.
This is one of the
few that is visible.
Extra-Solar Planets
Most extra-solar planets are
discovered through the “wobble”
they create in their parent star’s
Extra-Solar Planets, cont
Others are discovered through the periodic
dimming of the parent star’s luminosity.
Extra-Solar Planet Orbits/Masses
These 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
About 500 are
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