A 17-year-old intern, Wolf Cukier, discovered a planet on his third day on the job, NASA reported recently. Cukier’s summer internship was at the NASA Goddard Space Flight Center in Greenbelt, Maryland. Exoplanet hunting has had major successes only in the last 25 years.
According to the NASA article, Cukier’s initial job was to measure variations in star brightness in stars captured by NASA’s Transiting Exoplanet Survey Satellite (TESS). While working on the star system TOI 1338, Cukier initially mistook the new celestial body as a stellar eclipse, but then realized it was a planet. Additionally, it’s TESS’s first documented circumbinary planet, meaning it orbits two stars instead of one. Although Cukier made the discovery last summer, it was only recently discussed at a panel at the 235th American Astronomical Society Meeting in Honolulu.
Despite humanity’s lengthy history of stargazing, exoplanet science has only gained traction since the 1990s.
Birth of Exoplanet Science
In the 1940s, scientific technology developed to the point that astronomers could detect planets orbiting faraway stars. Unfortunately, it took another 50 years to successfully find one that could be proven and verified, which only happened in 1995 due to further advancements in Doppler radar technology.
“Michel Mayor and Didier Queloz—two astronomers from the Geneva Observatory in Switzerland—had been improving the emission lamp technique for Doppler measurements,” said Dr. Joshua N. Winn, Professor of Astrophysical Sciences at Princeton University. “Because their measurements were only good enough to find giant planets, they thought they were in for a very lengthy project, lasting decades because giant planets in the solar system all have orbital periods of a decade or more.”
“But they found their first planet after just a few months.”
According to Dr. Winn, the planet found by Mayor and Queloz appeared to be at least the size of Saturn or Jupiter, but its orbit around its star—51 Pegasi—only seemed to be 5 percent of the distance between the Earth and the Sun. And this orbit, like Cukier’s newly discovered circumbinary planet, gave the planet a first-of-its-kind quality.
“Being so close to the star, the planet around 51 Pegasi would be heated to nearly 2,000 degrees Fahrenheit,” Dr. Winn said. “That’s a temperature that’s usually associated with a small star, not a planet. This was our first glimpse at a so-called ‘hot Jupiter.'”
How Doppler Got Its Groove
Mayor and Queloz made their discovery due to the state of Doppler technology in 1995, but the road to their hot Jupiter actually began in the 1980s.
“By the 1980s, a few astronomers realized that the technology was almost good enough to detect planets, and they began pursuing different ways to get just a little extra boost in Doppler precision,” Dr. Winn said. “One of the toughest problems to overcome is wavelength calibration.”
With wavelength calibration, Dr. Winn said, the goal is to obtain several accurate images of a star, spaced out over time, and analyze differences in the wavelengths of its “stellar absorption lines,” also called Doppler shifts. However, when taking these long-exposure pictures of stars and their wavelengths, many outside elements can interfere, from the camera lens getting a speck of dust on it to the starlight entering the camera from a slightly different angle. Better wavelength calibration neutralizes these issues.
“Two pioneers of precise Doppler work were Gordon Walker and Bruce Campbell at the University of British Columbia in Canada,” Dr. Winn said. “They had a clever idea for wavelength calibration: Before the starlight goes into the camera, make it go through a container of some gas. The gas will have its own spectral absorption lines; its molecules all absorb their own favorite wavelengths of light.”
By doing this, both absorption lines—that of the gas and of the star—will be shown at once, so if the camera itself shifted somehow, both the gas lines and the star lines would shift together. “If you see the star’s lines shift but not the gas’s, then you can be pretty sure that’s due to the motion of the star, not just the rattling around of your telescope and your camera,” Dr. Winn said. “This trick is called the absorption cell method for precise Doppler measurements.”
The absorption cell method isn’t in use anymore—now, NASA detects planets by the tiny eclipses of stars by their planets, like Cukier was studying when he found his planet—but it was an important step towards the birth of exoplanet science.
Dr. Joshua N. Winn contributed to this article. Dr. Winn is the Professor of Astrophysical Sciences at Princeton University. After earning his Ph.D. in Physics from MIT, he held fellowships from the National Science Foundation and NASA at the Harvard-Smithsonian Center for Astrophysics.