NASA recently announced that the Hubble Space Telescope, when observing in ultraviolet, spotted ejections of material from the surface of Jupiter's moon Europa. It is widely believed that these ejections are geysers of liquid water spewing out through cracks in the surface ice of the moon, providing strong supporting evidence that there is indeed a vast subterranean ocean on Europa.
This alien ocean is estimated to be 100 kilometers deep, or about 10 times the depth of the deepest parts of the ocean on Earth. Here on our home planet, where there is water, there is life. But Europa has another thing going for it that makes it more intriguing than other moons that likely harbor liquid oceans—such as two of Jupiter's other moons, Ganymede and Callisto, as well as Saturn's smaller moon Enceladus, which also has liquid geysers.
The brownish-orange streaks on Europa's surface are thought to be deposits of salts, colored by the large amounts of electromagnetic radiation emitting from Jupiter and possibly deposited by the same water plumes that the HST spotted. (The Cassini spacecraft found evidence that the liquid water on Enceladus might also be salty). If this is the case, it would mean the ocean on Europa is in with a rocky seafloor. This is unlike the situation on, say, Ganymede, where researchers believe there is another layer of ice below the liquid water.
As a new episode of explains, the probability that there is life on Europa is much higher if its ocean is salty and in with a mineral-rich rocky seafloor. The process by which organic chemicals make the jump to reproductive life, known as abiogenesis, is still a mystery. But vast ecosystems of marine life—including tube worms, crabs, and even types of octopuses—thrive on Earth's seafloor near hot, sulfur-rich hydrothermal vents. Jupiter's gravitational pull provides enough energy to keep Europa's ocean in a liquid state, and it may be that it also provides enough energy to drive the geologic processes that produce hydrothermal vents.
It has been hypothesized that , which would make it even more likely that similar vents on other worlds could support and even create life. If life spawned around deep ocean vents on Europa's seafloor, it could have spread to cling to the underside of Europa's icy crust, just as single-celled organisms thrive in the crevices of Antarctic ice sheets. Evidence of that life might just be present in Europa's water plumes or even on the surface.
To find out for sure, we would need to send a spacecraft to investigate, which is why NASA is planning a probe tentatively known as the Europa Clipper for launch sometime in the 2020s. The orbiter would scan the moon for clues and scout out a good spot for a future lander. However, in NASA's 2016 budget, Congress offered more money than NASA requested for a Europa mission—provided they include a lander from the get-go and launch by 2022.
We will have to wait to see how NASA decides to proceed, but given the public interest in Europa and the fact that private researchers are trying to figure out a way to build an autonomous underwater explorer to send to the Jovian moon, we could see the Europa life question answered sooner than anyone thought.