We all know that comets are small icy bodies that on rare occasions enter the inner part of the Solar System and put on a stunning show as the ice vaporizes and becomes visible to us on Earth.  But I hadn’t given much thought to what those small, icy bodies look like without their gaseous envelopes until  NASA’s EPOXI mission spacecraft had a close encounter with comet Hartley 2 earlier this month.

So I started doing a little research.  Turns out, comets are made of rock, frozen gases (CO2, methane, ammonia), water ice, and dust.  Meaning….a lot of miscellaneous stuff – think of the pile of dust that comes out of your vacuum cleaner all clumped together when you empty it.  Since they are relatively small – between 100 meters to 40 kilometers across – they have relatively little mass.  This means that they don’t have enough gravity to pack all that stuff into a neat round ball.  So, they take on a variety of shapes including the bowling pin shape of comet Hartley 2. For more pictures of comet Hartley 2, visit NASA’s EPOXI mission.