Twenty-five years ago, humanity first witnessed a collision between a comet and a planet. From July 16 to 22, 1994, enormous pieces of the comet Shoemaker-Levy 9 (SL9), discovered just a year prior, crashed into Jupiter over several days, creating huge, dark scars in the planet’s atmosphere and lofting superheated plumes into its stratosphere.
The Double Asteroid Redirection Test (DART) – NASA’s first mission to demonstrate a planetary defense technique – will get one chance to hit its target, the small moonlet in the binary asteroid system Didymos. The asteroid poses no threat to Earth and is an ideal test target: measuring the change in how the smaller asteroid orbits about the larger asteroid in a binary system is much easier than observing the change in a single asteroid's orbit around the Sun. Work is ramping up at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, and other locations across the country, as the mission heads toward its summer 2021 launch – and attempts to pull off a feat so far seen only in science fiction films.