The evidence of a planetary system outside our Sun was captured a century ago but the astronomers didn't know what was right under their noses. The 'recent' re-discovery came from Carnegie Observatories' Collection of a white dwarf observation.

The white dwarf called van Maanen's star was discovered by renowned astronomer Adriaan van Maanen in 1917. The 1917 white dwarf observation plate was created by Walter Adams, the former director of the Mount Wilson Observatory, which was then part of the Carnegie Observatories.

The 1917 plate included an observation that the white dwarf appeared warmer than our solar system's Sun. Nothing from the observation seemed out of place. But the 1917 plate was not what it seemed.

White dwarfs are older stars like our sun that are near the end of their lives. The "stellar spectra" are the documentations of light produced by distant stars. When a spectrum passes through things on its way to the Earth, it leaves a trail of clues for astronomers.

In the 1917 plate, a new research found "missing pieces" in the spectrum's absorption line. This suggested that the spectrum passed through an interfering object.

They also found the presence of calcium, iron and magnesium in the van Maanen's star spectrum. Normally, these heavier elements should have disappeared into the old star long ago. Scientists did not expect that they would have a lot of planetary debris surrounding them at this late stage in their lifetime.

Back then, researchers didn't know that these white dwarfs with heavy elements present in their stellar spectra are actually planetary systems with vast rings of planetary debris.

Scientists only concluded this type of planetary system - polluted white dwarfs - within the last 12 years so the observation in the 1917 plate went under the radar for so long.

"The mechanism that creates the rings of planetary debris, and the deposition onto the stellar atmosphere, requires the gravitational influence of full-fledged planets. The process couldn't occur unless there were planets there," said Jay Fahiri from the University College London.

Last year, Fahiri contacted Carnegie Observatories to look for a plate on van Maanen's star. Carnegie's astronomical plate archive is one of the biggest in the world. Who knows what else they have in the basement and what today's researchers will find from observations in the past that went under the radar?