Three of Jupiter’s four largest moons are icy, and in 1998 NASA’s Galileo spacecraft detected tantalizing signs of an ocean beneath one, Europa. Since then, more studies have detected signs of possible erupting plumes of water from this ocean. The other two great icy moons, Ganymede and Callisto, are also believed to have oceans beneath their surface. Now new questions are being posed: If there is water on these moons, could there be life? And could we look for it? To help answer that question, the European Space Agency plans to send a spacecraft to Jupiter in 2022, called the Jupiter Icy Moons Explorer (JUICE).
Scheduled to arrive in 2029 , it will make multiple flybys of Europa and Callisto before entering orbit around Ganymede between 2032 and 2034, the first spacecraft to orbit a moon other than Earth’s. During this time, it will return invaluable data to Earth. However, before it gets there, scientists are already busy studying these moons for signs of habitability and preparing for the data that the mission will return.
Caught
The oceans under these moons are probably large, spanning the circumference of entire moons and stretching tens of kilometers deep. But they are also trapped under dozens of kilometers of ice, making them very difficult to study. One of our best approaches so far has been to look for the effects of salt in the oceans on their electrical conductivity by studying the magnetic fields around moons. But these studies “have mostly neglected all the other effects that generate magnetic fields,” said Professor Joachim Saur, a planetary scientist at the University of Cologne, Germany, such as thin atmospheres around moons. “It is very important to unravel the effects that really come from the ocean.” Prof. Saur is the coordinator of the project on Exo-Oceans, who hopes to answer this question. The project uses models and data from NASA’s Galileo spacecraft, which orbited the Jovian system from 1995 to 2003, along with measurements from NASA’s Juno spacecraft currently on Jupiter and remote observations from telescopes such as Hubble, to examine these oceans.
“Our results will not nullify the idea of an ocean,” said Professor Saur of Europa and Ganymede, although he noted that they might question one about Callisto. But hopefully they can give a better indication of things like the thickness of the oceans, their salt content, and their distance from the icy layers above. All of this has important implications for the habitability of moons. In order to support life, it is believed that the oceans must be in contact with the rock at the bottom for life to have a source of “food”, and it is currently believed that only Europe meets that condition . “Europa is one of the best candidates for habitability because liquid water is in direct contact with the silicate mantle,” said Professor Saur. “Therefore, there is a possibility that minerals from the crust may seep into the ocean. And the richer in chemical compounds, the better for the evolution of life. “ But there is much that can be done before JUICE arrives. Once it does, your magnetometer instrument will provide useful measurements on the magnetic fields of the moons, giving us vital data on the oceans below. “This will allow us to separate all the different effects,” says Saur.
Radiation
Another important factor regarding the habitability of the moons is the amount of radiation from Jupiter that receives them. Jupiter produces a lot of harmful radiation, so much so that it can damage spacecraft that get too close. One way to study this is to look at auroras on moons, which occur when Jupiter’s charged particles hit the magnetic fields around them. Europa, for example, has a constant aurora that can be seen in Hubble’s ultraviolet images. “It relates to how the moon is exposed to this radiation because the charged particles of the radiation create the aurora,” said Dr. Lorenz Roth, a planetary astronomer and physicist at the KTH Royal Institute of Technology in Stockholm, Sweden. “So it’s kind of a measure of how much radiation there is .” Dr. Roth worked on the AuroraMHD project, which sought to use some of these auroral observations of Europa and Jupiter’s volcanically active moon, Io, to learn more about them. While the project was hampered by the Covid-19 pandemic, it did provide some useful data.
In particular, he helped confirm the existence of plumes of water in Europa and investigated how they interacted with its atmosphere. And it is hoped that this work can be harnessed, with JUICE, to further study the habitability of Jupiter’s icy moons. “The issue of habitability and life always remains on the back burner,” said Dr. Roth. “In all respects, including size, Jupiter’s large moons are like planets: they are similar to or larger than Mercury, you have a magnetic field, you have atmospheres, you have oceans (and so on) . “Europe is more promising (because its) water is most likely connected directly to the rocky material at the bottom of the sea, allowing some reaction to take place.” JUICE will be equipped with its own ultraviolet instrument that could study the auroras of the moons in more detail, helping scientists figure out how radiation from Jupiter could affect their chances of life. “Once JUICE is in orbit, we will get a lot of information,” Dr. Roth said. “It can continuously measure the magnetic fields around the moons.”
Potential habitability
On its own, JUICE is not expected to definitively tell us if there is life on Jupiter’s moons. But their data, along with NASA’s Europa Clipper mission arriving in the Jovian system at a similar time to study Europa, could provide useful information about its potential habitability. In the same way that initial missions to Mars assessed its habitability, before later missions, such as NASA’s newly landed Perseverance rover, were sent to search for life, similar research could also be conducted for Jupiter’s moons. “While JUICE and the Europa Clipper have yet to launch, there are already discussions about what could be next,” said Professor Saur, such as landers that use drills to penetrate the ice and sample these oceans. . “Work is already underway in parallel on what the next steps might be,” he said.
Original article
This article was originally published in Horizon, the EU Research and Innovation Magazine
