Is there intelligent life out there?

A famous Fermi problem, called the Drake equation, puts the number of life forms, depending on who you ask, at around 2.

I am not so sure these days. Exactly 15 years, perhaps to the day, after Shoemaker-Levy 9 struck Jupiter, something else hit the planet and left an Earth sized hole. This time though, no one saw it coming, and no one is sure what actually hit the planet.

Is there a lot more activity in space, even now, than we think? How long until something hits us again?

The man who found the hole in Jupiter thinks this is evidence that the planet is really important for our own survival:

Mr. Wesley told the Sydney Morning Herald that spotting the impact mark on Jupiter made him glad the huge planet is in Earth’s neighborhood: “If anything like that had hit the Earth it would have been curtains for us, so we can feel very happy that Jupiter is doing its vacuum-cleaner job and hoovering up all these large pieces before they come for us.”

How many other life forms in the galaxy have been wiped out because they didn't have a giant hoover next door?