Transcript Asteroids - Discovery Space

Asteroids
On-line Lesson
On-line Lesson: Asteroids
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.
On-line Lesson: Asteroids
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.
On-line Lesson: Asteroids
• 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
On-line Lesson: Asteroids
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.
On-line Lesson: Asteroids
Different types
By 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
carbonaecous
S contain more
silicates
On-line Lesson: Asteroids
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.
On-line Lesson: Asteroids
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.
On-line Lesson: Asteroids
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.
On-line Lesson: Asteroids
Have they hit us before ?
Many scientists
believe that asteroids
have hit the Earth
many times
in its history.
Artists impression of a
giant asteroid impact
On-line Lesson: Asteroids
• 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.