Astronomers are puzzling over a strange white spot that recently appeared in the clouds of Venus, the BBC reports. The European Space Agency’s Venus Express spacecraft confirmed the spot, originally noticed by an amateur stargazer on July 19. Data suggests it appeared 4 days before that and has been steadily expanding since.
Scientists aren’t sure what caused the spot, though they suspect volcanic activity. It’s long been theorized that the planet was resurfaced by such activity, and some believe the eruptions are still occurring. But it would take an extremely powerful eruption to penetrate so high into the atmosphere. Other possibilities include charged particles from the sun interacting with the planet’s atmosphere, or atmospheric turbulence bringing bright material together.