Background to the 2019 Nobel Prize in Physics

Fifty percent of the 2019 Nobel Prize in Physics goes to Michel Mayor and Didier Queloz for the discovery of 51 Pegasi b!  I had a tweet thread on the topic go viral, so I thought I’d formalize it here (and correct some of the goofs I made in the original).

A hearty congratulations to Michel Mayor & Didier Queloz, for kickstarting the field that I’ve built my career in! Their discovery of 51 Peg b happened in my senior year of high school, and I started working in exoplanets in 2000, when ~20 were known.

A thread:

The Nobels serve a funny place in science: they are wonderful public outreach tools, and a chance for us all to reflect on the discoveries that shape science. The discussions they engender are, IMO, priceless.

They also have their flaws: because they are only be awarded to 3 at a time, they inevitably celebrate the people instead of the discovery.

(This technically a requirement from Alfred Nobel’s will, but there are other requirements, like that the discovery be in the past year, that the committee ignores. Also, the Peace Prize is regularly awarded to teams, but the science prizes have never followed suit.)

Anyway, many of the discoveries awarded Nobels are from those who saw farther because they “stood on the shoulders of giants.” The “pre-history” of exoplanets is a hobby of mine, so below is a thread explaining the caveats to 51 Peg b being the “first” exoplanet discovered.

The first exoplanet discovered was HD 114762b by David Latham et al. (where “al.” includes Mayor!) in 1989. It is a super-Jupiter orbiting a late F dwarf (so, a “sun like star” for my money), published in Nature:

https://www.nature.com/articles/339038a0

Dave is a conservative and careful scientist. At the time there were no known exoplanets *or* brown dwarfs, and they only knew the *minimum* mass of the object, so there was a *tiny* chance it could have been a star. He hedged in the title, calling it “a probable brown dwarf”.

I wonder: if Dave had been more cavalier and declared it a planet, would *that* have kickstarted the exoplanet revolution? Would he be going to Stockholm in a few months?

Meanwhile, Gordon Walker, Bruce Campbell, and Stephenson Yang were using a hydrogen fluoride cell to calibrate their spectrograph. In 1988 they published the detection of gamma Cephei Ab, a giant planet around a red giant star:

https://ui.adsabs.harvard.edu/abs/1988ApJ…331..902C/abstract

They were also very careful. At least four of the other signals reported there turned out to be spurious. They did not claim they had discovered any planets, just noted the intriguing signals. In follow up papers they decided the gamma Cep signal was spurious. Turns out it was actually correct!

Again, what if they had trumpeted these weak signals as planets and parlayed that into more funding to continue their work? Would they have confirmed them and moved on to stars with stronger signals? Would they be headed to Stockholm?

Moving on: in 1993 Artie Hatzes and Bill Cochran announced a signal indicative of a giant planet around the giant star beta Gem (aka Pollux, one of the twin stars in Gemini).

Like gamma Cep A, the signal was weak. Like Campbell Walker & Yang, they hedged about its reality. But again, it turns out it’s real!

https://ui.adsabs.harvard.edu/abs/1993ApJ…413..339H/abstract

Then, in 1991 Matthew Bailes and Andrew Lyne announced they had discovered an 10 Earth-mass planet around a *pulsar*. This was big news! Totally unexpected! What was going on!? They planned to discuss in more detail in a talk at the AAS that January.

But when the big moment came, Bailes retracted: they had made a mistake in their calculation of the Earth’s motion. There was no planet, after all. That made more sense. He got a standing ovation for his candor.

But in the VERY NEXT TALK Alex Wolszczan got up and announced that he and Dale Frail had discovered *two* Earth-massed planets around a different pulsar! They would later announce a third, and that remains the lowest mass planet known.

Some wondered: Was this one really right? Had they done their barycentric correction properly? It held up. The first rocky exoplanets ever discovered, and the last to be discovered for *20 years*.

And there would be more. In 1993 Stein Sigurdsson and Don Backer interpreted the anomalous period second derivative of binary millisecond pulsar PSR 1620-26 as being due to a giant planet. This, too held up.

https://ui.adsabs.harvard.edu/abs/1993ApJ…415L..43S/abstract
https://ui.adsabs.harvard.edu/abs/1993Natur.365..817B/abstract

Meanwhile, in a famous “near miss”, Marcy & Butler were slogging through their iodine work. They actually had the data of multiple exoplanets on disk when Mayor & Queloz announced 51 Peg b, but not the computing power to analyze it.

If you’re interested in more detail, you can read this “pre-history” in section 4 of my review article with Scott Gaudi here:

https://arxiv.org/abs/1210.2471

None of this, BTW, is meant to detract from Michel & Didier’s big day. 51 Peg b was the first exoplanet with the right combination of minimum mass, strength of detection, and host star characteristics to electrify the entire astronomy community and mark the exoplanet epoch. As I wrote above, they kickstarted the exoplanet revolution. It makes sense that Mayor & Queloz got the prize!

This is to make sure that the Nobel serves its best purpose: educating, and promoting and celebrating scientific discovery.

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