On the morning of 10 October 1995, the professor was driving along the long, winding road. He had every reason to feel emotional. He had spent four long nights at the observatory on Mount Wilson, a mountain top near Los Angeles. And for four nights, he had observed the same star. There was no other conclusion possible: the report from Italy was right.
He had previously scrapped the star from his list. It was different in size and composition to the Sun; it wasn’t the kind of star around which he expected to find planets. The professor was only interested in stars that did resemble the Sun, and he had more than 100 on his regular schedule. Every night he drove to the telescope to observe them. He had a research programme that had already been running for twelve years, the last seven of which he had spent on non-stop observation. His aim was to see at least one of the stars make a movement that would indicate the presence of a massive planet.
He didn’t expect to be able to confirm such a movement for perhaps 20 or 30 years: after all, the most massive planet in our solar system, Jupiter, had an orbital period of twelve years. Before the world would believe that he had discovered a planet around another star, he would have to observe at least two orbits. Until now, he had not seen any of the stars on his list make any suspicious movements. But he held on tightly to his long-term perspective: the secret was to keep observing patiently. His colleagues were sceptical, to say the least. But the professor kept his sights on the horizon and steadfastly went on observing, observing and more observing.
Five days earlier, a colleague had called him from Florence. What he told him had given him four sleepless nights. ‘Have you heard the news?’ he had said. ‘Two Swiss astronomers at a conference here claim they have discovered a planet around the star 51 Pegasi. Half the size of Jupiter. With an orbital period of four days. Four days, not years. Do you know anything about that?’
It couldn’t possibly be true. It completely defied all the predictions. And there had been earlier ‘discoveries’ of planets that proved false. For hundreds of years, it had been assumed that our solar system was the standard for all other stars. If they existed, large planets around other stars would take tens of years to complete an orbit. Like Jupiter, which has an orbital period of almost twelve years. The Swiss astronomers must have made a mistake.
The professor did not hesitate, and drove straight to the mountain. He had four nights of observation left over from his last programme. If the Swiss claims were true, he could observe exactly one orbit of the planet around 51 Pegasi. His expectations were low. Surely everything that scientists had agreed on for so many years couldn’t be wrong? Surely his strategy, which was to give him the world premiere as the first to discover an exoplanet, couldn’t have failed? Could it be possible that a couple of Swiss researchers – the fact that they were French-speaking perhaps made it even worse – had beat him to it?
And the star had moved. In four nights, it had moved back and forth. That could only mean that there was something rotating around it, something half the size of Jupiter. The professor realized immediately that the Swiss astronomers were right. They had discovered the first planet outside our solar system. It was watertight.
He had been scooped. They had got there first and whipped the prize from right under his nose. He had devoted his career to this discovery and now he had come in second. He had not discovered the first exoplanet. You would at least expect him to spit out a curse or give his a car a good kick. But, eighteen years later, Geoffrey Marcy remembers exactly how he felt as he drove down from the mountain that morning: ‘I felt delighted.’
Planetenjagers 3D
Planet Hunters 3D
“There are thousands of planets like the Earth out there, hundreds of lightyears distant, waiting to be discovered. Ellerbroek describes this exciting adventure, which is now entering a new and very significant phase, in colourful detail.”
Nobel Prize Physics 1999,
Professor theoretical physics (UU)
“A compelling adventure full of surprising details that show why astronomy is so fascinating..
Professor mathematical physics (UvA),
Director and Leon Levy Professor (IAS, Princeton)
“In this timely book by Lucas Ellerbroek, the characters who have participated in the discovery of these other worlds share their personal stories. Discoveries are made by individuals, thanks to their vision, enthusiasm and perseverance, and also through friendship, collaboration and competition. Planet Hunters is a lively fresco of that international endeavour. .
Professor of Astrophysics (University of Geneva),
Discoverer of the first exoplanet
“Planet Hunters by Lucas Ellerbroek provides dozens of delightful (and sometimes humorous) histories of individuals who thought and wrote about planets and life around other stars before the recent discoveries provided facts. It is both informative and a pleasure to read. I highly recommend it..
Kepler Principal Investigator (NASA Ames Research Center)

“Ellerbroek has written a captivating, up-close-and-personal chronicle of this remarkable burst of discovery. .
Senior Astronomer (SETI Institute)

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