If there was a competition for the most interesting moon in our solar system, Callisto would be a contender. Jupiter’s second largest moon has more influential craters on its surface than any other planetary body in the solar system, and has tons of ice on its surface as well.
For decades. Researchers have theorized that resting under the surface of Callisto’s pocket is a liquid water ocean that includes the whole moon. After taking a closer look at the data from 30 years ago, researchers now have stronger evidence than such an ocean really exists.
A team, led by Corey J. Cochrane of the inner planetary group and the Group Geophysics on NASA’s JPL, did not start looking for an ocean in Callisto. According to Cochrane, the team was working on another project, including Neptune Triton’s moon scan to see if there is an ocean below the surface.
This presented a challenge, due to the intense tritone ionosphere, which is the last layer of the atmosphere before space begins. Since Callisto also has an intense ionosphere, the team decided to test their methods in the 30-year measurements obtained from the NASA Galileo mission. That mission started in 1989 and scanned Jupiter and his moons between 1995 and 2003.
“Our conclusions were made possible by analyzing the measurements that were acquired by a callisto flight that is usually neglected in the community due to the presence of ‘noise’ growth attributed to the plasma environment,” Cochrane Cnet told an email.
“We were able to use plasma previously developed to remove this dark source of plasma noise from measurement so that the signal from the ocean could be analyzed independently,” Cochrane said.
In short, Galileo’s readings were initially difficult to interpret due to Callisto’s strong ionosphere. After Cochrane and his team cleaned the readings, they were able to consider the data, and this strongly suggests that there is an ocean below the rocky part of the moon.
Ionosphere looks like an ocean
It is so much time to prove the existence of an ocean below the surface in Callisto because a strong ionosphere imitates the readings that you would get if there were such an ocean.
“A basic physical law of nature (Faraday Law of Magnetic Induction) shows that if you move a magnet in relation to any conductive material, such as a copper wire, you will create an electric current within that wire that is synchronized in the movement of magnets,” Cochrane explained. “This current will create a secondary magnetic field (due to the movement of electrons in the wire) which is called an induced magnetic field, which shows the properties of the conductive material.”
Cochrane said this also works with planetary bodies. Moon or planets with sufficient internal heat can have a liquid ocean with salt water under the surface. These oceans are electrical conductors thanks to salt in the water. Thus, scientists can use magnetometers to measure an induced magnetic field that “preserves the properties of the ocean,” Cochrane said. In other words, the oceans can be found based on the magnetic fields they generate.
Since the moons like Jupiter’s Callisto and Neptune Triton have very strong ionosphere, readings with a magnets become so loud that researchers have trouble understanding whether what they are watching is an ocean or just a random noise from extra energy to ionosphere. That is why researchers have stuck in Callisto’s possible underground ocean for decades.
Next steps
Science will not have to wait another 30 years to find evidence. NASA’s Europa Clipper mission sailed last year and must reach Jupiter and its moons in 2030, while the European Space Agency’s mission should reach in 2031. Both missions will almost certainly provide more callisto research data.
As for the information they will collect, Cochrane told us that they are not necessarily different data. On the contrary, there are more data.
“Existence of the existence of the Callisto ocean from new measurements simply descends into the fact that there are more measurements available to analyze,” Cochrane said. “For each flight that occurs for each of these missions, only a very small photograph at the time of the magnetic field environment is captured by the magnetometer.”
Cochrane said data from Clipper’s missions and Europe’s juice will help “complete the holes” from the Galileo mission, hoping that leaving researchers finally prove if there is an ocean in Callisto. Additional data will also help researchers appreciate how thick the Callisto ocean layer is, as well as the thickness of the ice shell that rests on top of it.
Could there be life in callisto?
NASA and the European Space Agency would not have sent missions to Jupiter without good reason to do so. And one is this: Europe’s hidden waters are the first leader for extraterrestrial life.
“It is possible that the ocean of Europe can support life because we know that it expects the main ingredients to support it, those who are water, essential chemical elements and energy (eg heat source from within) over a period of time to evolve,” Cochrane said. “Europe Clipper is actually a residential mission (not to be confused with the discovery of life) which will provide the required data to help us better answer this question. By that time, it is difficult to comment on whether it is possible.”
But there is a growing occasion for life in Callisto. It has a surprising amount of oxygen and no one can understand where most of it came from. Setting that with the growing likelihood of an ocean below the surface, and though it is still far from a safe thing, this is enough evidence to justify taking a closer look at Jupiter Moon when missions arrive in 2030 and 2031.