In 1994, Glen Wurden watched several huge pieces of Comet Shoemaker-Levy 9 crash into Jupiter, generating an explosion big enough to see from Earth. "Had they hit Earth, we would not be standing here today," said Wurden in a recent talk at MIT.

Wurden is a fusion researcher at the Los Alamos National Laboratory, and an amateur astronomer by night.

A large fragment of Comet Shoemaker-Levy 9 caused a bright explosion as it hit Jupiter in 1994. Such an impact on Earth would have been devastating.

Although the risk of a giant, civilization-ending space rock hitting Earth is very low, the threat is always there (just ask the dinosaurs). And according to Wurden, there may be only one way to stop it: fusion rockets. That kind of technology is decades away, but Wurden asserts that we urgently need to invest in making it real.