The evidence comes from the NASA spacecraft Juno and its journey from Earth to Jupiter a few years ago. Scientists working on the mission weren’t looking for the dust that contributes to zodiacal light, or any kind of dust, but it smacked right into the spacecraft. Juno’s cameras captured images full of mysterious streaks, “like someone was shaking a dusty tablecloth out their window,” John Leif Jørgensen, a Juno scientist and professor at the Technical University of Denmark, explained in a recent statement. The streaks turned out to be pieces of Juno’s solar panels floating in space; dust particles had slammed into the panels at high speed and chipped them off. By the look of the spacecraft fragments, the bombarding particles were about the same size as the ones associated with zodiacal light.
It seems counterintuitive that the empty void all around us can be a dusty place, but it’s true, and “the inner solar system is certainly dusty in comparison to the outer solar system,” Hope Ishii, a professor at the Hawaii Institute of Geophysics and Planetology, who was not involved in the new research, told me. Juno wasn’t designed to hold on to these particles or study them. But scientists could examine the flurry that occurred along Juno’s journey and use it to learn about the particles’ origin and distribution across space. Their calculations suggested that, to create the dusty landscape Juno experienced, the source of the particles must have a certain set of orbital dynamics, and the only spot that matches up is in the vicinity of Mars.
This doesn’t mean that the glow Rhoades captured was made by dust particles straight from the surface of Mars. Scientists don’t know how such particles could manage to escape the red planet’s gravity and sail away into space. The researchers have floated the idea that the dust could have originated on Mars’s two moons. (Yes, Mars has moons. Most planets in our solar system do, and, at the risk of offending Earth, theirs are more interesting than our own.) Phobos and Deimos—irregularly shaped, more like lumpy balls of cookie dough than marbles—are thought to resemble asteroids, the same kinds that scientists believe sprinkle dust through the solar system. But dust from these moons would have a difficult time breaking away too.
“It’s really difficult to envision how this dust could be coming from Mars or its moons,” Larry Nittler, a cosmic-dust expert at the Carnegie Institution for Science, who was not involved in the research, told me. But “dynamically, it seems to be right.”
Juno’s solar panels survived their stint as accidental dust detectors, and today the probe is in orbit around Jupiter, capturing stunning views of the giant planet’s swirling storms. Cosmic-dust experts must now mull over the discovery they made, and astrophotographers like Rhoades might view the glow of the zodiacal light a little differently.