Occasionally a comet makes the newspaper headlines when it makes a dazzling light show across our night sky. This gives the impression that comets are rare. However, that’s far from the truth!
In reality, thousands of comets have been discovered in our Solar System and many more waiting to be found. And now we’re finding hundreds of comets around other stars, too! These are called ‘exo-comets’.
Like planets, comets orbit their star. Unlike planets they are born in the outer edges of a solar system, far away from the star’s heat and light. They are made out of rocks packed together with ice, like a dirty snowball.
As a comet get closer to its star, the ice begins to melt and rises from the surface like steam. The steam forms a cloud around the comet that can stretch out for 80,000 km! That’s the length of almost eight Earths in a row!
For thirty years astronomers have been watching with fascination at the strange, flickering light of a young nearby star. We now know that this strange twinkling effect is caused by hundreds of comets passing in front of the star!
As they pass in front of the star’s surface, each comet’s solid centre and hazy steam-cloud briefly block some of the star’s light. Nearly 500 exo-comets have already been discovered orbiting the young star!
Around 4,000 comets have been counted in our Solar System, but its believed that the true number could be more like a trillion! (That’s a million million!)