Enlarge Image NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill

Gas-giant planet Jupiter may be radically different from Earth, but we have some important molecules in common. Scientists have been eager to learn more about the abundance of water in Jupiter's atmosphere, and NASA's Juno spacecraft is finally offering up some answers.

There's a history to this mystery. NASA's Galileo probe dove into Jupiter's atmosphere in 1995. The data it sent back "suggested Jupiter might be extremely dry compared with the sun (the comparison is based not on liquid water but on the presence of its components, oxygen and hydrogen, present in the sun)," said NASA in a statement on Tuesday. This was way less water than researchers had expected to find.

Juno science results published this month in the journal Nature Astronomy update the story of water. The Juno data shows that water makes up around 0.25% of the molecules in Jupiter's atmosphere at its equator. That's three times that of the sun.

This new information suggests the Galileo mission just happened to sample a particularly dry part of Jupiter's atmosphere.

"Juno's surprise discovery that the atmosphere was not well mixed even well below the cloud tops is a puzzle that we are still trying to figure out. No one would have guessed that water might be so variable across the planet," said Juno principal investigator Scott Bolton.

NASA is using Juno to learn more about the origin and evolution of Jupiter, which also illuminates the story of our solar system's beginnings. This water data will help scientists assess leading theories about Jupiter's formation.

Juno, which has been in residence at the gas giant since 2016, will continue to peel back the layers of Jupiter's water mystery. "Just when we think we have things figured out, Jupiter reminds us how much we still have to learn," said Bolton.