In 2010, scientists waiting to use the William Herschel Telescope in the Canary Islands captured a brief 36 minutes of images of Venus. They were waiting for the sun to set so they could look at distant stars and dust disks around young stars. Consequently, little attention was paid to the data, which was filed away in the archives.

Hidden in the archives Fast-forward more than a decade, and researchers from the Netherlands decided to look at the old observations. What they discovered, hidden in the data, was a series of faint, planetwide concentric rings in the upper atmosphere. Their findings are published in a paper in The Planetary Science Journal.

The team analyzed images captured with ExPo, a highly sensitive instrument designed to measure polarized light. They compared ordinary images with polarized images taken through several visible-light filters to search for patterns that might reveal hidden atmospheric features.