A massive volcanic eruption has been seen on Jupiter's moon Io that could have covered more than 30 square kilometres of its surface.
Io is one of the most geologically active worlds in the Solar System - as well as being the fourth largest moon orbiting any planet.
A rocky world about the same size as our Moon, with very low gravity, Io is constantly being pulled between Jupiter and its other satellites - Europa, Ganymede and Callisto - leading to extreme tidal heating underneath its surface.
There are more than 240 volcanic regions on the moon, and when they explode they tend to release huge amounts of energy (up to 5 terawatts, according to New Scientist) - and send lava high into the air. As a result, researchers are constantly watching in case something spectacular happens.
And it appears something has. An eruption registering in the top 10 events ever seen on the moon has exploded in the Rarog Patera region, named after a Czech fire god.
"It is a very energetic eruption that covers over a 30 square kilometre area," said Dr. Imke de Pater, Professor of Astronomy and of Earth and Planetary Science at the University of California according to Phys.org.
"For Earth, that is big, and for Io it is very big too. It really is one of the biggest eruptions we have seen."
The eruption was spotted with the Keck II telescope - which itself is located on a volcano, on Mauna Kea in Hawaii - earlier this month.
But no pictures or video of the event have been released. Eruptions on the moon can't be seen directly from Earth and are only able to be detected with extremely sensitive infrared sensors.
Nasa confirmed that the eruption had sent lava spewing hundreds of metres into the air on the Moon, and said it was the biggest seen since 2001.