Circular rainbow seen on Venus

New Scientist : Glories are completely circular rainbows that can only be seen from above, and they often form concentric rings. They are caused by the backward reflection of light off of particulate matter that is spherical and all roughly the same size. In 2011 Wojciech Markiewicz of the Max Planck Institute for Solar System Research in Gottingen, Germany, and his colleagues were using the Venus Express satellite to observe Venus’s atmosphere when they saw the first glory ever spotted on a planet other than Earth. The researchers were hoping to see glories because they may provide a clue to what in Venus’s atmosphere is absorbing UV light. The glory that Markiewicz’s team saw was 1200 km in diameter, meaning that it was caused by material of consistent particulate size covering at least that same area. They suggest that the glory could have been caused by sulfuric acid droplets covered in elemental sulfur or mixed with ferric chloride.