Heidi B. Hammel, 48, an M.I.T.-educated planetary astronomer, has two professional missions. The first is to learn everything possible about those icy planets, Neptune and Uranus. The second is to communicate knowledge about space to ordinary citizens. In 1994, when the Shoemaker-Levy 9 comet crashed into Jupiter, Hammel was the leader of the ground team that analysed photos of the event from the Hubble Space Telescope. She was also the National Aeronautics and Space Administration’s public face, explaining the science to television audiences worldwide. We spoke at her home in Ridgefield, Conn., and later by telephone.

NASA is preparing a mission that will do one last repair of the Hubble Space Telescope. Afterward, if Hubble malfunctions, it will be allowed to die. Does that trouble you?
I’ve been working with a team planning the next great space observatory, the James Webb Space Telescope, scheduled for launch in 2013. Webb will be able to probe regions of the cosmos that are simply not visible to Hubble. With Webb, we have the potential to answer questions about the origins of just about everything in the universe.

Do you think astronomers are something like detectives—or investigative reporters?
Yes. We are most happy when we find something that doesn’t fit our expectations. In 1989, when Voyager 2 flew by Neptune, we saw, for the first time, a great dark spot in that planet’s southern hemisphere. I went to an Earth-based telescope to look at it in real time and the dark spot wasn’t visible. All I could see were these bright clouds alongside where the dark spot was supposed to be. Then in 1993, all the bright stuff was now in the northern hemisphere. A year later Hubble pictures showed the southern dark spot was gone. So far, it hasn’t come back. We don’t know why. But we did learn something new: that Neptune could change dramatically in just five years.

... contd.