Gizmodo: In 2015 Jay Farihi of University College London requested a 1917 glass plate from the Carnegie Observatory for an article about planetary systems around white dwarfs. The plate contains an image of the spectrum of the white dwarf known as van Maanen's star. Photographic glass plates were used in the late 19th and early 20th centuries to study the chemical composition of stars. Farihi spotted an absorption line in the spectrum, indicating that something with a variety of heavy elements such as calcium, magnesium, and iron had blocked the star's light. White dwarfs having that sort of absorption pattern probably host rocky planetary systems. Farihi's find predates the next earliest known evidence of a probable exoplanet by more than 70 years.
