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View from a killer asteroid (W. Hartmann) |
Asteroid Ida |
A collision with an asteroid could be even more devastating than a comet collision.
Comets are icy snowballs with low tensile strength - they fragment easily, and would
dissipate some energy through ablation within the atmosphere (but airbursts
can also be very destructive).
Asteroids are made of rock and/or iron - much higher strength material, so a larger
fraction survives to impact.
Most asteroids are confined within the `asteroid belt' - between the orbits of Mars and Jupiter. A relatively small number, however, follow orbits which take them through the inner Solar System. At present, ~160 are known: there may be as many as 2000 with diameters exceeding 1 km. An impact with such a body would have global implications.
This is almost certainly the fate meted out to the dinosaurs - the Cretaceous/Tertiary
impact (iridium layer) suggests a 10-km scale impact. See
this site and
the New Scientist dino page. We may even have found a piece of the
killer asteroid.
expected frequency - once per 100 million years
The dinosaur killer is associated with the Chicxulub crater, a 170-km diameter crater lying off the Yucatan peninsula. Nuemrous other terrestial impact craters are known: see this link.
More terrestial impact craters pictured here.