This rainbow-like phenomenon found on Venus is unprecedented—both in its beauty and its ability to help scientists solve a long-standing puzzle about the contents of Venus’s foggy skies.
In 2011, Wojciech Markiewicz and his team sent the European Space Agency’s Venus Express on a mission to find this optical oddity. Glories are similar to rainbows, but they forms in concentric circles and can only be viewed from above.
On July 24, 2011, they spotted one. They vetted their findings for many months before finally publishing them last month in the journal Icarus. A full glory has never been seen before on another planet, Markiewicz told New Scientist in an interview.
Here’s Phil Plait, writing for Bad Astronomy:
A glory is an optical phenomenon, where light is bent by tiny droplets in the air. This is similar to how a rainbow works, but in this case the exact mechanism is still under debate. For the effect to work the Sun has to be directly behind the observer and shining into a bank of liquid droplets. The light gets broken up into its individual colors, which form concentric circular halos centered on the shadow of the observer’s head (or more technically the anti-solar point). They’re pretty commonly seen from airplanes; I’ve observed them many times when the Sun is shining down on the opposite side of the plane, and I can see clouds and the plane’s shadow out my window.
The size of the halo and the colors depend on the size of the droplets and the amount they bend light, which depends on the chemical composition of the droplets. On Earth, of course, we’re talking water, but on Venus it’s not so easy. The majority of the atmosphere there is carbon dioxide, but there are a myriad of other molecules floating around there as well, making it rather difficult to determine what’s what in the thick murk.
The image from the Venus Express might be able to help scientists answer that question. We’ve known for decades that Venus’s atmosphere contains clouds of sulphuric acid, and they could be responsible for glories. But variations in brightness of the glory’s concentric rings suggest that more chemical components are at work.
One of them might be an ultraviolet absorber that accounts for spooky dark markings that astronomers see in Venus’s cloud tops. If true, the Venus Express captured one glorious image.