As far as modern-day astronomy is concerned, the first confirmation of exoplanets outside our solar system came when a team spotted two planets orbiting a star back in the early 1990s. But apparently an astronomer actually spotted the first exoplanets back in 1917 -- we just didn’t realize it.
As io9 notes, new research by UCLA physics and astronomy professor Ben Zuckerman has determined that Dutch astronomer Adriaan van Maanen seemingly spotted one of the first white dwarf stars 14 light-years away while working at the Mount Wilson Observatory near Los Angeles. The star was named “van Maanen 2.” It turns out that the first evidence of the existence of exoplanets was actually tucked away within van Maanen’s research notes.
Here’s an excerpt from the Physics arXiv Blog breakdown of Zuckerman’s discovery:
The photosphere of a white dwarf should contain only hydrogen and helium, which is what the spectra of a standard white dwarf shows. Anything else that falls into the star should rapidly sink beneath the surface and so be unlikely to show up.
But the spectrum of van Maanen 2 contains evidence of all kinds of heavier elements.
In recent years, Zuckerman and other astronomers have shown that these elements can only come from rocky debris orbiting the star. In other words, these elements come from asteroids regularly falling into their parental white dwarf and burning up.
These elements show up in the spectra of lots of white dwarfs. Indeed, various studies of the spectral characteristics of this debris have revealed the make-up of asteroids orbiting other stars for the first time.
One question that Zuckerman and others have puzzled over is why asteroids are regularly falling into white dwarfs. And this has led them to a fascinating discovery.
It turns out that all of these white dwarfs are surrounded by rocky debris and at least one large planet. It is the gravitational perturbations from this planet that cause the asteroids to collide with each other and then spiral into their parent star....When [astronomers] find white dwarfs with heavy elements in their spectra, they now consider this good evidence of an extrasolar planet.
It’s absolutely amazing the difference some hindsight can make when we look back at research done almost a full century ago. Van Maanen was on the right track, but no one could figure out exactly what he was looking at.
Let’s keep digging, scientists — who knows what other breakthroughs could be hiding in those dusty notebooks?