New astronomy from old sources: Planetary system found in a photographic plate from 1917.

Science Daily reveals how a century-old spectrographic analysis is probably the first ever evidence of an alien planetary system:

bout a year ago, the review’s author, Jay Farihi of University College London, contacted [Carnegie] Observatories’ Director, John Mulchaey. He was looking for a plate in the Carnegie archive that contained a spectrum of van Maanen’s star, a white dwarf discovered by Dutch-American astronomer Adriaan van Maanen in the very year the plate was made.

Stellar spectra are recordings of the light emitted by distant stars. Spectra spread out all of the component colors of light, like a rainbow from a prism, and they can teach astronomers about a star’s chemical composition. They can also tell them how the light emitted by a star is affected by the chemistry of the things it passes through before reaching us on Earth.

Carnegie’s 1917 spectrum of van Maanen’s star revealed the presence of heavier elements, such as calcium, magnesium, and iron, which should have long since disappeared into the star’s interior due to their weight.

Only within the last 12 years has it become clear to astronomers that van Maanen’s star and other white dwarfs with heavy elements in their spectra represent a type of planetary system featuring vast rings of rocky planetary remnants that deposit debris into the stellar atmosphere. These recently discovered systems are called “polluted white dwarfs.” They were a surprise to astronomers, because white dwarfs are stars like our own Sun at the end of their lifetimes, so it was not at all expected that they would have leftover planetary material around them at that stage.

“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.