03 Asteroids
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Transcript of 03 Asteroids
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Asteroids
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What are they?
• Asteroids are solid pieces of rock that have been left around the Solar System from the time when the planets formed.
• They range in size from one metre ( or perhaps smaller ) up to 1000 km.
• Asteroids are quite irregular in shape and therefore the light they reflect from
the Sun fluctuates as they move and rotate.
Asteroids
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What do they look like ?• We have never seen any asteroids close up
but in a telescope they look like a tiny point of light.
• Unlike comets, they have no cloud of diffuse
light around them.
• Because they are very cold they don’t emit much radiation themselves but they can be seen by very sensitive Infra-Red telescopes such as ISO.
Asteroids
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• Asteroids are very irregular in shape as these pictures taken from a spacecraft nearby show.
• They are quite similar to small planets or moons like Phobos
Asteroids
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How Many Are There?• Recent surveys using Infra-Red telescopes indicates
that in the main Asteroid belt around the Sun there are at least 1.1 million asteroids larger than 1 km.
Asteroids
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Different typesBy studying both the brightness and the reflectivity of certain colours it becomes clear that asteroids fall into several different groups.
M are believed to be metallic
C are thought to be carbonaceous
S contain more silicates
Asteroids
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Where are they?• Asteroids circle around the
Sun in orbits that trace their origins in the Solar System.
• The orbits of asteroids are more or less circular and they have orbital periods of three to six years.
• Not all orbits around the Sun are populated with asteroids because the motion of the main planets interferes with some orbits and makes them unstable for asteroids.
• The majority of asteroids are in the Asteroid Belt with distances from the Sun between 2.2 and 3.2 astronomical units.
Asteroids
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Detection • Looking for asteroids in a telescope requires a
search for objects which move from one night to the next and are point like in appearance.
• To be sure that it is an asteroid rather than a planet or comet, enough observations must be taken to be able to measure the mathematical parameters of the orbit.
Asteroids
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Are Asteroids Safe?• Asteroids pass through the Solar System in their
orbits, which can change with time as they are affected by passing planets.
• If an asteroid was deflected from its orbit onto a path that intersected that of the Earth, the results would be very serious.
• An object 100km across hitting the Earth at 20 km/sec would could immense damage.
Asteroids
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Have they hit us before ?
Many scientists believe that asteroids have hit the Earth many times in its history.
•
Asteroids
Artists impression of a giant asteroid impact
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• Because the effect of such a collision would be so dramatic, the signs of this can be seen in the geological record sometimes as huge craters.
• An event of this kind may have caused the atmospheric and climatic disturbance which led to the destruction of the dinosaurs.
Asteroids