Transcript Asteroids - Trimble County Schools

Asteroids
Definition
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Asteroids: relatively small, predominately
rocky objects that revolve around the sun
Name means “starlike bodies”
Sometimes referred to as minor planets or
planetoids
Asteroid Basics
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They move on quite eccentric trajectories
Most are found in the asteroid belt between
Mars and Jupiter
Few are larger than 300 km
All the asteroids masses together do not
equal the mass of the Earth’s moon
The asteroid Ceres
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The largest asteroid, at 940 km (1/10,000th
the mass of Earth)
Discovered in 1801 by Guiseppe Piazzi
Has a semimajor axis of 2.8 AU
More Basics
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Current number of known asteroids is over
200,000. Hundreds of thousands of others
may await discover.
All but one orbit in the same direction as
the planets
The asteroids are probably left over
material from the solar system’s formation
Jupiter’s gravity keeps the asteroids from
combining into a larger body
Physical Properties
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There are several different types
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C-type (carbonaceous) – darkest in color; found
more to the outside of the belt (75 %)
S-type - contains silicate or rocky material; found
more to the inside of the belt (15 %)
The largest ones are roughly spherical, but
the smaller ones are irregular
The asteroid Vesta
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Some Earth meteorites are thought to have
originated from Vesta – they are made of
basalt.
Unique in that it appears to have
undergone volcanism
Two other Asteroids to know
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Pallas – 580 km and Juno – 540 km
Asteroid Observations
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The Galileo space probe, headed for
Jupiter, went through the asteroid belt
twice.
In had close encounters with Gaspra and
Ida
Gaspra v’s Ida
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Both are S-type.
Gaspra is 20 km in size and Ida is 60 km.
Ida is more heavily cratered, because it is
in a denser part of the asteroid belt.
Ida is a billion years old, Gaspra just 200
million years old.
Both are thought to be fragments of once
large objects.
Gaspra
The neatest thing about Ida…
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It has a tiny moon, Dactyl!
Dactyl is just 1.5 km across.
It orbits about 90 km from Ida.
It is also an S-type asteroid.
`
Asteroid Ida and
tiny moon asteroid,
Dactyl!
Binary Asteroids
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Def: two asteroids orbiting one another as
they circle the Sun.
May be a result of collisions in the belt.
Less violent collisions may also be
responsible for the binary systems.
More violent ones may send asteroids into
Earth-crossing orbits.
Binary Asteroid 90 Antiope
The NEAR Spacecraft
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Stands for Near Earth Asteroid
Rendezvous.
In 1997, visited the C-type asteroid
Mathilde and S-type asteroid Eros.
Mathlide was calculated as having a fairly
low density, probably a result of being very
porous.
It rotates every 17.5 days.
Mathilde, Gaspra and Ida (for size
comparision)
The NEAR Spacecraft
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NEAR spent a year around Eros.
It was photographed many times.
It was found to be more solid (denser) than
Mathilde.
In February of 2001, NEAR landed on Eros,
sending back pictures as it did so.
Eros at sunset
Earth-Crossing Asteroids
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Most asteroids have a eccentricity of
between 0.05 and 0.3.
This means that they stay between Mars
and Jupiter.
Those having an eccentricity of 0.4 or more
(few) may intersect Earth’s orbit and are
known as Earth-crossing asteroids.
Earth-Crossing Asteroids
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As of 2004, more than 2600 of these
asteroids were known.
More than 600 are listed as “potentially
hazardous” – more than 150 m in diameter
and come within 0.05 AU of Earth.
1994 - 2004, more than 850 asteroids
passed within 15 million km of Earth.
At least 200 are predicted to pass within
that same distance in the next decade.
Earth-Crossing Asteroids
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Most will eventually hit Earth.
During a million year period, our Earth gets
struck by about 3 asteroids.
On average, 2 will hit water and 1 will hit
land.
The Moon, Venus and Mars all show
evidence of being hit by asteroids also.
Earth-Crossing Asteroids
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Most are about 1 km in diameter.
One 10 km one has been found.
How much of a problem would a 1 km
asteroid be if it hit Earth?
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Catastrophic!
Would devastate an area 100 km in
diameter.
The explosion would be equilvalent to a
million megaton nuclear bombs – one
hundred times more powerful than all of the
nuclear weapons on Earth!
How much of a problem would a 1 km
asteroid be if it hit Earth?
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The shockwave and possible tsunami
would affect an even larger area.
This is believed to have caused the
extinction of the dinosaurs.
But, don’t worry! We are watching the
skies for “problem” asteroids!
Trojan Asteroids
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Orbit at and beyond Jupiter’s orbit.
Several hundred of these are known.
Holes in the main belt?
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There are holes in the belt, where fewer
asteroid exist, known as Kirkwood gaps
(discovered by Daniel Kirkwood, 19th
century American astronomor)
These exist because of Jupiter’s gravity.
Red – Near Earth
Asteroids
Green –
other
asteroids
Blue squares – comets
Other blue – Trojan
asteroids
Dog-Bone
Shaped Asteroid
216 Kleopatra