I just found out that astronomer Steve Ostro has died. I didn’t know him personally, but many of my friends did. He was an asteroid specialist, and he was specifically interested in near-Earth and potentially hazardous asteroids. He was especially important in the field of active radar mapping of asteroids: using the giant Arecibo radio telescope to send pulses of energy at asteroids and using the timing of the reflections to make 3D maps, similar to how dolphins and bats echolocate. I’ve used many of his maps in my talks, including the dog-bone shaped Kleopatra (to show that not all asteroids look like spuds).