The 1917 photographic plate spectrum of van Maanen's star from the Carnegie Observatories’ archive. The pull-out box shows the strong lines of the element calcium, which are surprisingly easy to see in the century old spectrum. Carnegie Institution for Science

The first discovery of planets outside our solar system dates back to 1992, when a team of scientists discovered three planets orbiting the pulsar PSR1257+12. Now, new research has revealed that the renowned astronomer Walter Adams, way back in 1917, accidentally photographed an exoplanet orbiting the van Maanen’s star — a white dwarf located nearly 14 light-years from Earth.

The evidence of the century-old discovery was unearthed about a year ago, when Jay Farihi from the University College London contacted Carnegie Observatories Director John Mulchaey regarding a photographic plate in the latter’s archive that contained a stellar spectrum of van Maanen’s star.

“The unexpected realization that this 1917 plate from our archive contains the earliest recorded evidence of a polluted white dwarf system is just incredible,” 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.”

A stellar spectrum records light emitted by distant stars, and was widely used by late 19th and early 20th century astronomers to study a star’s composition. Additionally, by looking for gaps in absorption lines, scientists can gauge the chemical composition of the objects light from the star must have passed through, as different elements absorb lights of different frequencies.

When Farihi examined Carnegie’s 1917 spectrum of van Maanen’s star, he detected the presence of heavier elements, such as calcium, magnesium and iron — elements that had no business being there unless they were part of a planetary debris “polluting” the white dwarf.

“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 said in the statement. “The process couldn’t occur unless there were planets there.”

Scientists now believe that over 3 percent of all white dwarfs in the universe may be surrounded by remnants of terrestrial planetary systems. And, although we are yet to discover planets or their debris around van Maanen’s star, Farihi said it was “only a matter of time.”