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Astronomers Found Evidence for Exoplanets 100 Years Ago and Didn’t Know It

1917 photographic plate spectrum of van Maanen’s star from the Carnegie Observatories’ archive, showing evidence for “pollution” caused by rocky debris. Image: Carnegie Institution for Science
1917 photographic plate spectrum of van Maanen’s star from the Carnegie Observatories’ archive, showing evidence for “pollution” caused by rocky debris. Image: Carnegie Institution for Science

University archives are treasure troves of historic information, but it’s not every day they produce scientific discoveries. But now, a 1917 astronomical glass plate from the Cargenie Observatory’s collection is offering the oldest evidence for a planet orbiting another star—besting the first confirmed exoplanet detection by more than 70 years.

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It all started about a year ago, when Jay Farihi of the University College London contacted the Carnegie Observatory about a glass plate containing a spectrum of van Maanen’s star, a white dwarf photographed by renowned astronomer Walter Adams in 1917. Farihi was interested in studying the star’s spectrum for a review article about planetary systems around white dwarfs. He did not expect to find evidence for one.

Handwritten notes on the sleeve covering the astronomical plate in question. Image: Carnegie Institution for Science
Handwritten notes on the sleeve covering the astronomical plate in question. Image: Carnegie Institution for Science
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Today, astronomers use digital tools to capture starlight, separate it into its component colors, and decode the star’s chemistry. But in the 19th and early 20th centuries, if you wanted to learn about a star’s makeup, photographic glass plates were the only game in town. When Farihi analyzed this particular plate, he discovered something striking: an absorption line, indicating a missing slice of the spectrum where the star’s light had passed through an object and been partially absorbed.

The line revealed the presence of heavy elements, including calcium, magnesium, and iron in the vicinity of the star. Today, white dwarfs bearing this sort of “pollution signature” are considered strong candidates for rocky planetary systems.

“The unexpected realization that this 1917 plate from our archive contains the earliest recorded evidence of a polluted white dwarf system is just incredible,” Carnegie Observatory director John Mulchaey said in a statement. “And the fact that it was made by such a prominent astronomer in our history as Walter Adams enhances the excitement.”

It’s not the first time in recent months astronomers have learned something amazing from one of these aging snapshots of the sky. Earlier this year, Louisiana State University’s Bradley Schaefer examined photographic plates of a rather infamous stellar body—KIC 8462852, better known as the supposed alien megastructure—and discovered even more evidence that the star’s light curve is damn weird. Clearly, between hints of exoplanets and hints of Dyson spheres, it’s high time we gave the work of our pioneering astronomers a thorough review.

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[Carnegie Science]

Maddie Stone is a freelancer based in Philadelphia.

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DISCUSSION

Hmm question. If stars with orbiting bodies of sufficient size are considered polluted, then how many unpolluted stars are there?

Obviously, if and when we reach out to the stars, we’d prioritize going to polluted stars in search of planets habitable by man - that’s a given. But an unpolluted star, that’s not necessarily saying there isn’t a planet, it’s just saying we don’t have evidence of one.

Even if there isn’t a orbital body of sufficient size, it doesn’t mean an unpolluted star system won’t have resources or characteristics that we might be interested in.

So, what’s the proportion? If the majority of stars are polluted, then it’s less of a concern. But if the majority are unpolluted, potentially our instrumentality isn’t sensitive enough to detect things of interest.