Asteroids

The dwarf planet Ceres as seen from the Hubble Telescope.

Asteroids are probably one of the biggest threats known to humanity.  The right-sized asteroid colliding with Earth could release more energy than all the world’s nuclear arsenal.  It happened to the dinosaurs and it could happen to us.  For most astronomers it’s not a question of if this possible doomsday scenario will unfold, but when.

Our solar system is full of thousands of asteroids that orbit the sun just asEarth does.  Asteroids are pieces of the early solar system that never formed into the planets, as we know them now.  Most asteroids known to man can be found in the asteroid belt between Mars and Jupiter.  The belt formed because scraps of early planets that smashed together were never allowed to accrete into a planet, due to Jupiter’s massive gravitational force.  Material in the belt ranges in size from the dwarf planet Ceres (900km) to tiny dust particles.  Interestingly the material in the asteroid belt is so thinly distributed that unmanned space probes have traversed it without incident.  However collisions still occur in the belt, and if two asteroids collide, one could be knocked into the inner solar system towards Earth.

In the 1980s, as technology advanced, astronomers started to track any asteroid they could find in our night sky.  Below is a time-lapsed video showing how many asteroids are now being tracked from the initial 1980 tally of 8,954 asteroids.