Water is a crucial molecule for life but its importance in astronomy goes beyond aliens and habitability. Water is key to planet formation, so measuring how much there is around the Solar System helps us determine which theories of planet formation are the most accurate.
The amount of water within the atmosphere of Jupiter is a particularly sought-after number since the planet is the first to have formed in the Solar System. NASA’s Galileo collected some measurements in the '90s when it swan-dived into the gas giant and now, the Juno mission is carrying out a wider and more comprehensive study of the planet. As reported in Nature Astronomy, water molecules are estimated to make up 0.25 percent of the atmosphere of Jupiter.
The observations from Juno paint a new picture of the internal goings-on of the Jovian atmosphere. When Galileo went through its 57-minute descent, it measured some very peculiar things. First, there was about 10 times less water than expected. Secondly, this water increased with depth. The atmosphere was expected to be well mixed (ie have a constant water content), but that did not appear to be the case.
It seems that Galileo sampled a particularly warm and dry spot, but in general, the atmosphere of the planet is constantly churning and not at all homogenous. The incredible data from Juno has revealed as much.
"Just when we think we have things figured out, Jupiter reminds us how much we still have to learn," Dr Scott Bolton, Juno principal investigator at the Southwest Research Institute in San Antonio, said in a statement. "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."
The measurements in the new paper come from Juno's first eight flybys of Jupiter, which focused on the equatorial regions of the gas giant planet. On Monday, it performed its 27th close pass around Jupiter and its orbit has been shifting, covering more and more northern latitudes in detail.
"We found the water in the equator to be greater than what the Galileo probe measured," added Dr Cheng Li, a Juno scientist at the University of California, Berkeley. "Because the equatorial region is very unique at Jupiter, we need to compare these results with how much water is in other regions."
Juno will continue to orbit Jupiter until July 2021 when it will be deorbited and disintegrate in the planet's atmosphere.