Writing in Nature Astronomy on Monday, 18 November 2019, scientists have made the first-ever direct measurement of water vapour in the atmosphere of Jupiter’s icy moon Europa – one of 79 in total – which is thought to contain a vast ocean beneath its rugged surface.
Astronomers have known this since the 1960s and even predicted that radiation from Jupiter would reach the moon’s surface and lead to the formation of water vapour. While research conducted afterwards provided some indirect support for that being the case, this is the first direct evidence we have that Europa contains water vapour in its atmosphere.
Interestingly, the discovery almost didn’t happen, as the research team – working at the Keck Observatory in Hawaii – had failed to pick up on any infrared wavelengths indicating the presence of water on 16 out of the 17 occasions they’ve performed the measurements.
And yet, on 26 April 2016, the final day of the study, they had finally detected what they were looking for, and a lot of it to boot – around 2,000 metric tons of water vapour observed escaping the moon’s surface.
That being said, the research team is of the opinion that water vapour was likely present on the preceding nights as well, only in quantities too small for their equipment to detect. These measurements also suggest that Europa probably has less water than previously thought, much of which is likely expelled during one-off events, such as the one detected by the study authors themselves.
With these findings, the likelihood that Europa contains a large amount of water beneath the surface is now very high, yet the fact – if it is, indeed, a fact – will have to be confirmed during upcoming Europa Clipper and JUICE (Jupiter Ice Moons Explorer) missions.
“I’m really looking forward to follow-up studies on Europa and other ocean worlds,” said co-author on the paper and NASA planetary scientists Lucas Paganini. “It has been difficult to detect water in liquid form. These detections of water in vapour form, I think, is the closest thing we have in the search for liquid water environments.”