The mysterious 'glow' in Saturn's ring: Strange 'surge' is actually an optical illusion, astronomers reveal
A stunning new image released by Nasa’s Cassini spacecraft reveals a mysterious glowing spot in Saturn’s B ring.
The phenomenon is known as an ‘opposition surge,’ in which one particular region appears to be far brighter than the rest.
While it may seem unusual, the agency says the spot is actually an optical illusion produced by the Sun’s alignment with the observer.
According to Nasa, an opposition surge is the result of a combination of two factors when the Sun is directly behind an observer looking toward the rings.
This positioning creates a ‘region of opposition,’ in which the shadows of ring particles directly opposite the Sun from Cassini fall behind those seen from the spacecraft.
As these shadows become invisible to Cassini, all those which can be seen are in sunlight, making them appear very bright.
Outside of the region of opposition, the particle shad- ows are visible, darkening this area and causing the brightness to ‘ fall off in a circular fashion around the opposition point.’
Along with this, the effect seen in the images are caused by ‘coherent backscatter.’
In this type of optical phenomenon, the electromagnetic signal from the rays of scattered sunlight as it travels back to the craft is enhanced near the region of opposition.
According to Nasa, this happens because the electric and magnetic fields of the scattered radiation fluctuate in unison, rather than cancelling out.
The image just released by the agency was taken in visible light by the Cassini spacecraft on June 26, 2016 from roughly 940,000 miles away from Saturn.
It’s been seen before in Saturn’s A ring as well, in images captured on July 23, 2006, from 163,000 miles away.
And, Saturn’s glowing spot isn’t the only optical illusion produced by the craft.
In images released this past July, Nasa revealed what at first seems to be a major intergalactic accident – Saturn’s rings appearing to melt.
Saturn's A and F rings appear bizarrely warped where they intersect the planet's limb, whose atmosphere acts here like a very big lens.
'In its upper regions, Saturn’s atmosphere absorbs some of the light reflected by the rings as it passes through.
'But absorption is not the only thing that happens to that light,' explained Nasa.
'As it passes from space to the atmosphere and back out into space towards Cassini’s cameras, its path is refracted, or bent.
'The result is that the ring's image appears warped. (C) Daily Mail, London