Solar Orbiter Passes Through The Tail Of A Comet

The ESA/NASA Solar Orbiter is currently making a series of swings around the solar system so it can get closer to its eventual target, the Sun. While the scientific laboratory travels, it has the opportunity to investigate some other interesting subjects, too, including a comet it recently had a close encounter with.

Comets are chunks of mostly ice that get warmed up as they approach the Sun and give off gasses that form distinctive tails. Typically, they have highly elliptical (i.e., very oval-shaped) orbits, and they can come from the far depths of the solar system, changing very little over time. In light of that, the chance to investigate a comet up close is exciting, as it gives scientists the opportunity to get a glimpse of what the solar system might have looked like long ago.

Solar Orbiter passed through the tail of one such comet, called Comet C/2021 A1 Leonard, over the course of several days around December 17, 2021. ESA has now shared more information about the comet and what its researchers hope to learn from it.

The Solar Orbiter team was able to predict when the orbiter would pass through the comet's tail by looking at data about the solar wind, which are streams of energetic particles given off by the Sun. By entering data about solar wind into a program for modeling spacecraft and comet orbits, they could see when Solar Orbiter would intersect with the comet's tail.

The team used a suite of instruments on Solar Orbiter called the Solar Wind Analyser (SWA) to detect what chemicals were present in the comet's tail, finding ions of oxygen and carbon, molecular nitrogen, and molecules of carbon monoxide, carbon dioxide, and possibly water. The experts were also able to look at the way the solar wind affected the magnetic field around the comet, which is dragged out from the Sun's magnetic field.

This is the second time Solar Orbiter has come close to a comet, as it also passed through the tail of comet ATLAS in 2020. This time around, more of Solar Orbiter's instruments were online and ready to observe, gathering additional data that will help astronomers improve their understanding of comets.

"This kind of additional science is always an exciting part of a space mission," said ESA Project Scientist for Solar Orbiter Daniel Müller. "When the comet ATLAS crossing was predicted, we were still calibrating the spacecraft and its instruments. Also, the comet fragmented just before we got there. But with Comet Leonard we were totally ready – and the comet didn't fall apart."

With that encounter complete, Solar Orbiter will continue circling closer to the Sun, making its closest pass to date in March 2022 at around 30 million miles.