The Planetary Society was greatly saddened today to hear of the untimely death of radio astronomer Steve Ostro. I had never met Steve personally but I had interviewed him several times (see here, for instance) and made frequent use of his excellent website on the radio reconnaissance of near-Earth asteroids. He was a vocal advocate in support of the continuing operation of the world's greatest radio telescope, the Arecibo observatory, in the service of followup studies of the orbits of near-Earth asteroid, to retire the risk they may pose to Earth. He will certainly be missed by the planetary science community. Charlene Anderson has posted an obituary of Steve Ostro here, and Lou Friedman reflected on his role in the fight to save asteroid astronomy at Arecibo. Mat Kaplan interviewed him for Planetary Radio (here's the second part of the two-part show) as recently as January 1, 2007.