MONMOUTH, ILLINOIS (October 9, 2019) — With so many stars in space, it seems a certainty that plenty of those stars have planets orbiting them.
Yet, actually proving that "is ridiculously hard to do," said Monmouth College physics professor Mike Solontoi. That's why the science that's been pioneered by Michel Mayor and Didier Queloz was deemed worthy of the Nobel Prize in Physics, which the pair was awarded earlier this week by the Royal Swedish Academy of Sciences. A third physicist, Jim Peeples, also received the Nobel Prize for "theoretical discoveries in physical cosmology." "Peebles's honor was more of a lifetime achievement award," said Solontoi of the Albert Einstein Professor of Science at Princeton University. Solontoi explained that Mayor and Queloz's breakthrough came in the 1990s, but their discovery of an exoplanet orbiting a solar-type star has become even more Nobel-worthy in the past two decades. "The science that Mayor and Queloz pioneered has become an entire field," he said. "That's why it's getting the Nobel now. The science has gotten very good. We can now measure the velocity of a star at not much more than human walking speed." Indeed, since their discovery of 51 Pegasi b in 1995, a "revolution" has started in their field, with more than 4,000 exoplanets having been discovered in the Milky Way galaxy. Solontoi said the science behind the discovery is a type of "Doppler effect" for light. Known as the radial-velocity method, it relies on very slight changes in the color of light, with the light becoming slightly more blue as an object gets closer and slightly more red as it gets farther away. The method relies on the fact that a star does not remain completely stationary when it is orbited by a planet. "They found a four-day cycle for the red shift/blue shift," said Solontoi of Mayor and Queloz. "That little oscillation or wobble is caused by a planet pulling ever so slightly on the star as it orbits. They had both the chops to analyze their data and the expertise with their instrumentation." Conditions must be right for such a discovery, said Solontoi, and in the case of 51 Pegasi b, it was a Jupiter-sized planet with a very close orbit of its star. He said one doesn't have to look far to see a contrast to those optimal conditions. "Using that method, we could not find Neptune in Neptune's orbit," he said. "It takes well over 100 years for Neptune to orbit the sun. In 2011, it finally completed its first full orbit since it was discovered. Pluto, planet or not, has still not completed an orbit since it was discovered. The red-blue shift is not going to be noticeable in a scientist's lifetime." Peebles, meanwhile, developed a theoretical framework of the universe's history that is the foundation of our modern understanding. Included is a model that shows that only about 5 percent of the content of the universe is known, with the remaining 95 percent consisting of unknown dark matter and dark energy. "There are fundamental things in cosmology that we don't have an accurate explanation for yet," said Solontoi. On a related note, Solontoi said he often tells his students about a conversation he had with a "legitimate, brilliant cosmologist." "He said, 'Why do you want to get into cosmology? It's a dead subject.' Six months later, we learned about dark energy," he said. "I tell my students that story to teach them that you can still get really bad advice from people who are thought to be brilliant."