It was Oct. 6, 1995, in Florence, Italy. The conference was wrapping up, and the tone in the room was subdued, recalls Natalie Batalha. As a graduate student studying sunspots at the time, Dr. Batalha selected a seat at the back for the afternoon panel. She saw just one TV camera there to document the occasion. So when a Swiss astronomer who wasn’t on the schedule stepped up to speak, the gravity of his announcement didn’t sink in immediately.
“Maybe I was just too young and naive,” she recalls. “I couldn’t even imagine how that discovery would change the course of my career. It did in a very dramatic way.”
That day in Florence, Michel Mayor announced that he and Didier Queloz had made the first detection of a planet orbiting a star like our sun. Today, the discovery of 51 Pegasi b (affectionately called 51 Peg b by scientists) is hailed as the catalyst for a flood of research into worlds beyond our solar system, called exoplanets.
“They opened up an entire field of study that didn’t exist,” Dr. Batalha says. She personally shifted her focus to exoplanets in the wake of the discovery and is now a renowned expert in the field. And she’s not alone. The field exploded and today more than 4,000 exoplanets have been detected and confirmed.
On Tuesday, the legacy of the discovery of 51 Pegasi b was etched in gold when the Royal Swedish Academy of Sciences awarded Dr. Mayor and Dr. Queloz half of the Nobel Prize in physics. They share the award with cosmologist James Peebles, whose theoretical work underpins our understanding of the universe.
Taken together, the three scientists’ work triggered a revolution in our perception of the cosmos. Our view of the universe has gone from largely theoretical models to a complex picture of a dynamic system that is grounded in evidence.
Written in the stars
The discovery of 51 Pegasi b was no accident. Teams around the world were sifting through telescope observations of stars hoping to glimpse some signal that might be explained by a planet in orbit. But many were skeptical that technology was capable of making unambiguous detections – until 51 Pegasi b.
“It was kind of the turning point from believing ... to knowing. It’s transitioning from hypothesis to reality,” says Jessie Dotson, an astrophysicist at NASA’s Ames Research Center and the project scientist for NASA’s K2 Mission. “For me personally, it was almost like, ‘Oh thank goodness, we finally found one. Let’s go find the rest.’”
Once it was proved possible, exoplanet science took off and NASA was more willing to fund exoplanet research and flagship missions like the Kepler space telescope. That, in turn, led to many more discoveries, which inspired further research. The door was opened.
“When exoplanets first started, it was obscure, fringe, even laughable,” says Sara Seager, an astrophysicist at the Massachusetts Institute of Technology in Cambridge, and deputy science director for NASA’s latest exoplanet hunting mission, TESS. “Now that the field was awarded a Nobel Prize, I think it forces everyone who didn’t take it seriously to take it seriously.”
Strange new worlds
Before the discovery of 51 Pegasi b, our only idea of what planets might look like and how they form came from our own solar system. And the new planet gave astronomers a surprise. It orbits its star closer than Mercury does the sun and is at least half the mass of Jupiter. Based on the worlds here, we thought there was no way a massive planet could be found so close to its star.
“It was so unusual that people could not believe it at first,” says William Borucki, the principal investigator of the Kepler Mission that launched in 2009 to determine the frequency of Earth-size planets in the habitable zone of solar-like stars.
Dr. Borucki was another early exoplanet pioneer and worked for NASA for 53 years. “But ultimately it was proved that indeed it was a valid discovery. And so what [the discovery revealed] is that not only are there planets around other stars, but the planetary systems are very, very different from our own.”
Astronomers have discovered planets that orbit multiple stars, planets larger than Jupiter, lava worlds, ocean worlds, and worlds so unlike those that we know that scientists don’t yet know for sure what they look like.
“The diversity of planets in the galaxy far exceeds the diversity of planets in the solar system,” says Dr. Batalha, now a professor of astronomy and astrophysics at the University of California, Santa Cruz. “There are so many mysteries and so much diversity out there that it boggles the mind.”
Where we fit in
What is our place in the universe? That is one fundamental question that drives the explosion of exoplanet research.
We don’t really know the answer yet, says Dr. Seager. Solar systems like ours don’t seem to be common. But 51 Pegasi b ushered in an age in which we may actually be able to determine where we stand.
Similarly, Dr. Peebles’ research revealed that ordinary matter – the stuff stars, planets, and our bodies are made of – is a vanishingly small portion of the entire universe: just 5%. The remaining 95% is thought to be made up of dark matter and dark energy which largely remains a mystery.
“We’re pretty insignificant,” says Lyman Page, professor of physics at Princeton University. “This is all the Copernican Revolution taken to the next step.”
A head for heights
Dr. Peebles is considered a giant in cosmology. His work rocketed the field into relevance and prestige, says Edward Kolb, a cosmologist and a professor at the University of Chicago as well as the dean of physical sciences.
“When I came into cosmology it wasn’t something you would tell your mother, you’re a cosmologist,” he says. “It was somewhere between philosophy and astronomy and physics. It was not looked upon as a great thing to do. Jim really led the way in establishing cosmology as an anchor in modern astronomy and modern physics.”
Theory ruled in cosmology, and data was largely left to the physicists. But Dr. Peebles devised models that could be confirmed or denied by data. His models focused on placing cosmology in the context of the laws of nature and the laws of physics.
“He brought together a lot of classic physics and incredible deep insight to formulate what has become the standard model of cosmology,” says Dr. Page, whose office is next to Dr. Peebles’ at Princeton.
What resulted from Dr. Peebles’ work is the “Lambda cold dark matter model” of how the universe has been expanding since the Big Bang some 14 billion years ago. It explains in detail the structure of the universe, and underpins our current understanding of our place in the universe.
But Dr. Peebles’ legacy goes beyond his work, Dr. Kolb says. “I got a letter from Jim Peebles when I was a graduate student about something that I wrote and it was a great inspiration to me. He inspired people,” he says. “Everyone looks up to him, not just because he’s a very tall person.”
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