Artemis

 is a Black Hole badge. So far, its requirement is to suck a wewe. A Khan Academy staff member (Peter Collingridge) knows the method but has not shared any detail. One of his blog posts said it was currently impossible to acquire the badge.

Trivia

 * Artemis gives the most number of energy points than any other badge on Khan Academy.
 * The badge is named after Artemis - the Greek goddess of hunt, wild animals, wilderness, childbirth... Artemis is twin sister of Apollo - the god of the Sun; thus she is the goddess of the Moon.