5 July 2016
By Elizabeth Deatrick
New research into the movements of dust around Jupiter’s four largest moons could help scientists searching for life in our solar system, according to a new study.
Jupiter’s moons Io, Europa, Ganymede and Callisto were first observed by Galileo in 1610. Micrometeoroids smashing into these moons, and geysers erupting on Europa and Io, send thin clouds of icy dust rocketing off their surfaces. Some of this dust enters into orbit around Jupiter.
This moon dust around Jupiter could give scientists clues about the composition of the surface of these satellites, some of which scientists think could harbor life. But Earth-based telescopes and spacecraft flying by Jupiter haven’t yet been able to capture enough information on the dust particles to make accurate measurements of their behavior.
Now, scientists have turned to a computer model to track the movement of these dust particles. They’ve found the dust moves in surprising ways, according to the new study published today in Journal of Geophysical Research: Planets, a publication of the American Geophysical Union.
The dust particles segregate themselves by size, with smaller particles on the side of Jupiter trending towards the sun, with larger particles trending towards the dark side. In addition, some of the particles are pulled into retrograde orbit, circling Jupiter in the opposite direction of the majority of dust particles and the majority of bodies in our solar system.
This is the first time particles originating from the four prograde Galilean moons have been found in retrograde orbit—a “surprising” finding, according to Xiaodong Liu, a member of the Astronomy Research Unit at the University of Oulu in Oulu, Finland, and lead author of the new study. “This is new,” he added.
Retrograde particles are hard to find. “We have hints of this at Saturn, but because retrograde is a bit like driving the wrong way on the highway, the relative lifetime of these particles is quite small,” said Nicolas Altobelli, a planetary scientist with the European Space Agency (ESA) who was not involved with the study.
Jupiter’s moons might not be renowned for their orbiting dust the way Saturn’s rings are, but knowing more about the dust particles is critical for understanding if these moons could harbor life and planning future space missions, according to the study’s authors.
Since the dust particles are made mostly of material ejected from the moons’ surfaces, collecting and analyzing the composition of the dust will allow researchers to study the moons without ever landing on them.
The Europa Multiple-Flyby mission planned for 2022 is planned to include a dust-catcher, which scientists hope to use to learn more about the internal oceans of the moon below, said Juergen Schmidt, an astrophysicist at the University of Oulu in Oulu, Finland, and co-author of the new study. Mapping the trajectory of the dust around Jupiter ensures scientists that the dust they are capturing is representative of the moon below, and did not come from another moon, Schmidt said.
Calculating the density of dust particles around Jupiter could also help engineers plan for future space missions to Jupiter—specifically, the JUpiter ICy moons Explorer (JUICE) mission, due to launch in 2022. “[This study] was initially viewed as purely practical,” Altobelli said. JUICE will rely on solar panels for power—but as Altobelli pointed out, solar panels can be vulnerable to dust at high speeds, as are the antenna which allow satellites to transmit data back to Earth. A single dust particle could damage to a spacecraft travelling at high speeds—especially if it hit a vital system, according to the study’s authors.
“For a spacecraft, one single grain of a 1/10 millimeter in size could be fatal if it hits the right part,” Schmidt said.
In the new study, researchers built a virtual computer model of Jupiter and its magnetic field, its moons, the ambient plasma environment, and the sun. The model simulates icy dust particles of various sizes blasting off of the surface of the moons following micrometeoroid impacts. The study’s authors simulated more than 20,000 particles, using different particle sizes for each source moon.
The majority of the large dust particles fall back to the surface of their moons, re-impact their parent moons, with a few large particles colliding with the other moons and Jupiter, which the scientists expected.
But when the team looked at individual particles ejected from each source moon, they saw some strange behavior. They found that smaller dust particles shifted towards the sun. But larger particles, with greater surface area, were pushed toward the dark side of the planet by the sun’s radiation. The scientists were expecting the dust to be distributed evenly based on size.
The results suggest dust on the day and night side of Jupiter might have different compositions, and yield different information about the moon below, according to the study’s authors.
The team was also surprised to find that some of the particles went into retrograde orbit, circling Jupiter backwards. Almost all objects in our solar system orbit in the same direction, echoing the direction they were spun off in during the system’s formation. But in the course of the particles’ orbital evolution, the Lorentz force and solar radiation pressure pull some of the particles into orbits running counter to that of dust found elsewhere in our solar system, according to the study’s authors.
The team is currently looking into existing images of Jovian moons, taken by the Voyager and Galileo spacecrafts, to back up their model and potentially learn more about the particles’ behavior.
“There is still more we can do, exploring this model,” Schmidt said.
—Elizabeth Deatrick is a science writing intern at AGU.