Galileo, 1995, Page 2

Paul Geissler

Galileo flew past the Earth, and then it went to Venus, and it flew past the Earth, and then finally had enough speed to make it to Jupiter. On the way it made the very first-ever close flyby of an asteroid. This was a huge thing. Nobody had ever seen one up close before. As far as anybody had ever seen, they were single points of light in a telescope. We had no idea what we were going to find.

Because of the low telemetry rate, we had to send back little pieces of pictures to decide whether we wanted to send back the whole thing. We called these pieces of pictures “jail bars” because that’s just what they looked like. One of the early pictures of Asteroid Ida was these jail bars—with several of them, you could kind of make out the shape of the asteroid.

In one of the jail bars, way up above the asteroid, there was a little blip there. It was way to big too be an artifact; there wasn’t anything in the field of view. There had to be something else there apart from this asteroid.

William Merline

It turned out that one of those jail bars went right through the satellite. Of course we actually were looking for satellites in these images, but I don’t think anybody really expected to find any. It was clear it was a satellite because it had the same kind of shading that the asteroid had: It was bright on one side and darker on the other. That was pretty spectacular.

Paul Geissler

At the time we weren’t sure if we’d really discovered a moon of an asteroid, and we didn’t even know if such a thing could happen. We can’t even contain our excitement. It turns out within a couple of days one of the other instruments, the infrared imaging spectrometer, actually had detected the same thing. So with two different instruments we were damn sure there was something there. But we didn’t actually go public with it until there was a real press release from NASA.

In the meantime, we would see each other at science conferences. I made this beautiful color picture of Ida and the moon, Dactyl, and we’d make sure no one else was looking and I’d show them this picture. It was a great conspiracy for a little while, anyway.

Some pictures came down late on Friday. I was still there. This was a pair of images taken as Galileo was moving past the asteroid, and as the asteroid was rotating. So you’ve got two different perspectives, but pretty similar lighting. And they were a wonderful stereo pair. It was the first time anyone on this whole planet had ever seen an asteroid in 3-D. You could make out the blocks on the surface and little landslides and things like that.

I print these out—by now it’s like eight o’clock on a Friday—and I bring them home. I grab the stereoscope and bring that home, and I set it up and I pull out my chair. For that entire weekend, every kid that came to the door, the postman, anyone who was wandering by, I would drag them in and say, “Hey, you’ve got to see this!” I would tell them, “You’re the eighth human being to ever see that.” It was just a big kick to have that privilege. 

William Merline

We made the only actual images of the comet Shoemaker-Levy 9 impacting into Jupiter, because the spacecraft was in position where you could see the direct impacts, which you couldn’t see from Earth. It was pretty spectacular. Of course, we saw it from the Earth in all kinds of different data before we saw it in the Galilean images, because it took a while to bring the images back. But the images we saw from Earth were just plumes coming over the horizon on Jupiter. Once Jupiter rotated you could see the impact spots, but you couldn’t really see the direct impacts.

We made a plan for the Galilean imaging that tried to cover a lot of different scenarios as far as what the brightness might be of the direct explosions. When we finally got the images down, they were really stunning images. It was pretty spectacular to see them, first of all, but also to actually come up with a plan that allowed us to see them.