If you’ve ever driven through a snowstorm you know how disorienting it can be. Millions of flakes rebounding off your windshield. White-out conditions. It’s not so different for a spacecraft orbiting a comet.
The European Space Agency’s Rosetta mission had a similar experience, for more than two years, as it flew alongside Comet 67P/Churyumov–Gerasimenko between 2014 and 2016. Like a winter storm pelting your face with sleet and snow, the spacecraft endured the continuous impacts of dust grains launched from the 2.5-mile-wide comet as its dust-permeated surface was warmed by the heat of the sun. In outer space, heated ice doesn’t melt but turns directly from a solid to a gas, dragging the dust along for the ride. The scientific term for this is sublimation.
The photo was made two years ago January. At the time, Rosetta was closing in on the comet after keeping a safe distance since the previous August, when 67P was at perihelion (closest to the sun) and most active. We can only imagine the ferocity of dust storm the craft might have experienced at that time, perhaps powerful enough to damage cameras and other equipment.
Even 5 months later, it still looked a little crazy out there. Excessive dust in Rosetta’s field of view made navigation tricky, too. The craft’s star-trackers used the known positions of stars in the sky to fix its orientation with the respect to the sun and Earth, crucial for communications. Dust grains created occasional havoc because they’re tiny, bright specks that resemble stars. At times, the star-trackers locked on to dust grains instead of stars, creating pointing errors that occasionally put the spacecraft’s operations on standby or temporary safe mode.
Just like we can learn a lot about how snowflakes form by studying them up close, scientists used three of Rosetta’s instruments to study tens of thousands of grains up close, analyzing their composition, their mass, momentum and speed and profiling their 3D structure. The tiny grains, which were found to contain silicon, carbon, magnesium and sodium among others, are the tiny building blocks of comets.
Here are a few more comet dust storm images. If you have a bit more time, take a few minutes to go through the archive for some incredible photos of the comet.