Scientists Discovered Exoplanets More Than 70 Years Earlier Than Thought

A 1917 glass plate discovered in an observatory archive records the first evidence of exoplanets

exoplanet discovery
The 1917 photographic plate spectrum of van Maanen's star from the Carnegie Observatories’ archive. Carnegie Institution for Science

As far as astronomers knew, the first evidence for the existence of exoplanets, or planets outside our solar system, was recorded in the late 1980s and early 1990s. However, a glass plate recently discovered in the archives of the Carnegie Observatories in California shows that, unbeknownst to them, astronomers had been sitting on evidence of exoplanets since as far back as 1917.

It might seem like modern astronomers regularly announce the discovery of new planets outside of our solar system, but this wasn’t the case until recently. These days, astronomers rely on sophisticated instruments like the Kepler Space Telescope to detect exoplanets by searching for certain clues. But during the early 20th century, the only method astronomers had for studying the makeup of faraway stars was to photograph them on glass plates, like the one recently rediscovered by astronomer Jay Farihi, Maddie Stone reports for Gizmodo.

Farihi never intended to look for planets: he was actually trying to dig up old information about a particular white dwarf star known as “van Maanen’s star.” First discovered by famed astronomer Walter Adams in 1917, the star was recorded on a glass plate along with an image of its light spectrum.

Farihi was studying white dwarfs when he requested to see Adams’ plate. He examined the star’s spectrum to see what it was made of and realized that it contained heavy elements that shouldn’t have been there, like magnesium and iron, Andrew Moseman reports for Popular Mechanics. Upon closer inspection, he realized that they must have come from the shattered remains of a planet.

“The mechanism that creates the rings of planetary debris, and the deposition onto the stellar atmosphere, requires the gravitational influence of full-fledged planets,” Farihi says in a statement. “The process couldn’t occur unless there were planets there.”

The presence of these elements suggests that the white dwarf is surrounded by rocky debris left over from a planet that once orbited the star. While astronomers have yet to directly observe an exoplanet in orbit around a white dwarf, in recent years they have found evidence of rocky debris around similar stars, Elizabeth Howell reports for Discovery News. These “polluted white dwarfs” were a surprise at first, as scientists at first believed that white dwarfs were so old that any evidence of planets orbiting them would have been long-gone.

“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 Observatories director John Mulchaey says in a statement. “And the fact that it was made by such a prominent astronomer in our history as Walter Adams enhances the excitement.”

In recent years, observatory archives have been a treasure trove for scientists and historians alike. Just a few months ago, Danish astronomers dug up glass plates dating back to the 19th and early 20th century that documented solar eclipses and helped confirm Albert Einstein’s General Theory of Relativity. With hundreds of thousands of glass plates in the Carnegie Observatories’ archives, Mulchaey hopes they might hold more discoveries just waiting to be found.

“We have a ton of history sitting in our basement and who knows what other finds we might unearth in the future?” Muchaey says.

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