The existence of the spot was confirmed by Venus Express
Astronomers are puzzled by a strange bright spot which has appeared in the clouds of Venus.
The spot was first identified by an amateur astronomer on 19 July and was later confirmed by the European Space Agency's Venus Express spacecraft.
Data from the European probe suggests the spot appeared at least four days before it was spotted from Earth.
The bright spot has since started to expand, being spread by winds in Venus's thick atmosphere.
Scientists are unsure as to what caused the bright spot tens of kilometres up. However, a volcanic eruption is a possibility.
Much of the planet is thought to have been resurfaced by volcanism. Though no firm evidence for present-day volcanism has been discovered, scientists suspect it could still be happening on Venus.
But an eruption would have needed to be extremely powerful to penetrate this far through the planet's dense, mainly carbon dioxide, atmosphere.
Another potential source for the bright spot are charged particles from the Sun interacting with Venus's atmosphere.
Alternatively, atmospheric turbulence may have caused bright material to become concentrated in one area.
This is not the first time bright areas have been spotted on Venus. But this feature is unusual because it is confined to a relatively small region.
The spot was first identified by US amateur astronomer Frank Melillo, from Holtsville, New York.
Astronomers have recently been studying a "scar" on Jupiter, thought to have been caused by a comet or asteroid impact.