I’d almost argue this story should be a part of our What’s Up segment this week since it’s about an astronomy phenomenon photographers look for. But it’s actually a science story about that phenomenon. I’m talking about zodiacal light. It’s a faint glow in the sky just before dawn or just after dusk, that happens when sunlight is reflected toward Earth through tiny dust particles that are orbiting the Sun. I learned that these dust particles are the result of comets and asteroids shedding material when their orbits get too close to the Sun.

It’s basically the same cause as our meteor showers, except that we’re viewing the light through the dust from a distance instead of the Earth passing through the dust while we sky watch late at night.

Or so we thought. New research published in the Journal of Geophysical Research: Planets examines data from NASA’s Juno spacecraft that detected dust particle impacts as Juno traveled from Earth to Jupiter. The result is that the research team now thinks our zodiacal light is actually caused by dust particles from Mars.

The discovery was actually quite serendipitous, as the press release headlines claim. The instruments onboard Juno weren’t designed to find dust particles; they were designed to take images of the sky every quarter second. These images help determine Juno’s orientation in space by matching to star patterns, and that keeps the magnetometer’s measurements accurate. But lead author John Leif Jørgensen also programmed one of the cameras to report when an object was found in multiple images that didn’t match the catalog information. He was looking for undiscovered asteroids.

What he found was image upon image of tiny streaks appearing and then disappearing. After eliminating several possibilities, including a possible fuel leak from Juno, the team realized they were looking at interplanetary dust particles, and, due to Juno’s gravity assists, they were able to actually compile a distribution of those particles. The dust basically stretches from Earth to just beyond Mars. Earth, it seems, pulls in the closest dust particles, and that’s the cause of the zodiacal light. On the other end, Jupiter’s gravity grabs the particles.

The question remains, though, as to how Mars lost all these dust particles in the first place. It’s pretty interesting research that no one is really doing. In fact, research on zodiacal light is sparse enough that Dr. Brian May, of Queen fame, was able to complete in 2007 the thesis he started in the early 1970s because no one had really done anything in the field since. That thesis was titled A Survey of Radial Velocities in the Zodiacal Dust Cloud. Maybe he’ll help figure out this Mars question.

More Information

NASA JPL press release

“Distribution of Interplanetary Dust Detected by the Juno Spacecraft and Its Contribution to the Zodiacal Light,” J. L. Jorgensen et al., 2020 November 11, JGR Planets