NASA might have just discovered the world's best evidence to date of water on Jupiter's moon Europa.
The find didn't come from the Hubble Space Telescope or any of the other spacecraft currently in operation. Instead, these groundbreaking finds came from a flyby done by the now-retired Galileo Jupiter probe. Galileo hasn't been operable since 2003, and researchers estimate that the flyby that detected the plume was done in 1997.
NASA researchers said they compared the measurements from two decades ago and found that changes in the magnetic field and plasma around Europa uncovered by Galileo would parallel findings from Hubble a few years ago. A couple of years ago, the Hubble Space Telescope captured water vapor plumes, a hint there could be water on Jupiter. However, those readings couldn't be validated without Galileo's information.
Galileo was last seen in 2003 as it plunged its way into Jupiter's atmosphere to avoid colliding with Europa itself.
Europa is slightly smaller than Earth's moon in terms of size, but researchers have theorized for years that the satellite could hold twice as much water as what's found on Earth. Europa measures roughly 1,900 miles wide (approximately 3,100 kilometers). The water could be found deep in a global ocean beneath the moon's hard, icy exterior.
"We know that Europa has a lot of the ingredients necessary for life, certainly for life as we know it."
"We know that Europa has a lot of the ingredients necessary for life, certainly for life as we know it. There's water. There's energy. There's some amount of carbon material. But the habitability of Europa is one of the big questions that we want to understand," said planetary scientist Elizabeth Turtle of Johns Hopkins University Applied Physics Laboratory.
"And one of the really exciting things about detection of a plume is that that means there may be ways that the material from the ocean – which is likely the most habitable part of Europa because it's warmer and it's protected from the radiation environment by the ice shell – to come out above the ice shell. And that means we'd be able to sample it," Turtle said during a NASA briefing.
Europa is currently the most promising hope humans have at finding water outside of Earth. However, it's not the only place in the Milky Way where scientists are looking for water or signs of life. NASA's Cassini spacecraft has sampled plumes from Saturn's Enceladus. Those hydrothermal vents could have just the right conditions to be a similar environment to that of early Earth's.
For now, NASA, JPL and other researchers around the world will hopefully expand on Galileo's findings. NASA is planning a closer look at Europa during the Europa Clipper mission slated for June 2022. A new craft will be responsible for gathering plume samples and getting better readings as to whether or not Europa could hold a promise of water -- and possibly life.