By David Soderblom, Astronomer at STScI
It’s exciting to witness history being made, especially if it’s a long-awaited event. The afternoon of October 6, 1995 was that time. Several hundred astronomers were in Florence, Italy for the ninth in a series of scientific meetings on Cool Stars, Stellar Systems, and the Sun. The Cool Stars series was started by Andrea Dupree in 1980 in Cambridge, Massachusetts, and they continue to be held every two years. Cool Stars 9 was the first to be held outside the U.S., and Roberto Pallavicini from Florence’s Arcetri Observatory led the group that organized and hosted the meeting.
Florence is a delightful place to be under almost any circumstances: warm, sunny, good food, and great sights. But everyone was very focused that afternoon. In the morning we were told that there’d be a special short talk later, and the buzz over lunch was that Michel Mayor of the Geneva Observatory, working with Didier Queloz, had a rock-solid detection of a planet around another Sun-like star to report.
When we returned to the meeting hall after lunch I made sure to get a seat up front. Nobody really knew anything yet, just that a big announcement was coming. We all knew Mayor and Queloz were searching for planets, so what else could it be? But which star, and what kind of planet? All the brighter Sun-like stars were well known to many of us, so it was probably a star we’d heard of and studied ourselves.
We then had to sit through most of the afternoon’s scheduled talks; they were selected to be interesting in the first place, but at this point were being eclipsed by the Main Event. As the time grew near for Mayor’s presentation some people with television cameras started filtering into the back of the room. Mayor showed us his observations and conclusions, and there was little to argue with. There was warm and enthusiastic applause: the prey so long sought had been nabbed.
So why did it take so long? It’s been pointed out that 51 Pegasi, the host star to this planet, was misclassified as being evolved. But that in itself wouldn’t preclude detecting the planet that was found. A big part of the reason is simply that 51 Peg B – the planet – was so very different than anyone ever expected. Or, to be more precise, it was located where we did not think we’d find planets: close in to the host star.
The conventional wisdom was that other planetary systems would be like ours, with analogs to Jupiter at great distances and with long periods that would take years of careful measurements to detect. At the time I imagined the process Mayor and Queloz must have gone through. They’d been observing 51 Peg and stars like it for some time, hoping to see very small changes in the motions of the stars that would indicate a planetary companion. 51 Peg showed larger variations than they could make sense of, so they started observing it more often, maybe every month instead of a few times per year. And still, 51 Peg showed some kind of motion going on but with no clear period. So they started observing it every week, and still no period to the variations. It was only when they measured it every night for a few weeks that the 4.2-day period became blindingly obvious. They had it!
Once the realization dawned that these “hot Jupiters” could exist so close to a star they became fairly easy to find because they produce much larger signals than more distant planets. The race was on and over the next several years there were dozens and dozens of new exoplanets announced by Mayor’s group and a competing group led by Geoff Marcy in California. There was no turning back. History was made.
Scientific meetings like Cool Stars 9 often feature an invited talk at the end by a senior researcher who provides a summary of the high points and his or her views on their significance and implications for the near future. That person that time was Jeff Linsky, from Boulder CO. But Linsky played hooky to visit museums the afternoon that Mayor made his presentation and so he missed it. His conference summary mentions nothing of the one talk that will be remembered longest.
Finally, it is now nearly 20 years since Cool Stars 9. I was conscious of events at the time, but the details are getting fuzzier, and the recollections of others may sound different.