Transcript PowerPoint Presentation - AST121 Introduction to Astronomy

Pluto, Comets, and Space Debris
Chapter 8
Topics
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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
• 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
50,0
00190,0
00
AU
Cloud
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
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normal rate: few per hour
meteor shower: >50 per hour
trails of space debris left by comets
When should you look?
Leonids
• Predictions; NASA
Leonid 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