Solar Orbiter Spacecraft Catches a Second Comet by the Tail


For a spacecraft designed to conduct unique studies of the Sun, Solar Orbiter is also making a name for itself exploring comets. For several days centered on 1200-1300 UT on December 17, 2021, the spacecraft found itself flying through the tail of Comet C/2021 A1 Leonard.

Solar Orbiter's View of Comet Leonard in Visible Light Annotated

A composite of Comet Leonard images captured December 15-16, 2021, in visible light by the Metis instrument onboard the ESA/NASA Solar Orbiter spacecraft. The comet transited across the field of view with its dust and ion tails pointing towards the instrument. Credit: ESA/Solar Orbiter/Metis Team

The encounter captured information about the particles and magnetic field present in the tail of the comet. This will allow astronomers to study the way the comet interacts with the solar wind, a variable wind of particles and magnetic field that emanate from the Sun and sweep through the solar system.

The crossing had been predicted by Samuel Grant, a post graduate student at University College London’s Mullard Space Science Laboratory. He adapted an existing computer program that compared spacecraft orbits with comet orbits to include the effects of the solar wind and its ability to shape a comet’s tail.

Tasting a Comet's Tail

This plot series represents data collected by the Solar Wind Analyser’s Heavy Ion Sensor as the ESA/NASA Solar Orbiter spacecraft passed through Comet Leonard’s tail in December 2021. The data cover December 11-20, with the first and last plot before and after the tail crossing, respectively, marked by an absence of singly ionized ions. During the tail crossing the instrument detected particles that are attributable to the comet rather than the solar wind, for example ions of oxygen, carbon, and molecular nitrogen, and molecules of carbon monoxide, carbon dioxide, and water. (Ions are atoms or molecules that have been stripped of one or more electron and now carry a net positive electrical charge.) Credit: ESA/Solar Orbiter/SWA team

“I ran it with Comet Leonard and Solar Orbiter with a few guesses for the speed of the solar wind. And that’s when I saw that even for quite a wide range of solar wind speeds it seemed like there would be a crossing,” he says.

At the time of the crossing, Solar Orbiter was relatively close to the Earth having passed by on November 27, 2021, for a gravity assist maneuver that marked the beginning of the mission’s science phase, and placed the spacecraft on course for its March 2022 close approach to the Sun. The comet’s nucleus was 44.5 million kilometers away, near to the planet Solar Wind Through a Comet's Tail

This data plot uses solar wind speed and direction data from the Solar Wind Analyser’s proton and alpha sensor (SWA-PAS) to estimate how close the ESA/NASA Solar Orbiter spacecraft approached to the center of Comet C/2021 A1 Leonard’s ion tail during December 2021. The plot records how close each packet of solar wind detected by SWA-PAS is thought to have got to the comet’s nucleus during its journey from the Sun to the spacecraft. The left axis gives the scale in astronomical units (au), where 1 au is the distance from the Sun to the Earth, and the same distance is shown in kilometers on the right axis.
Changes in the solar wind flow speed and direction are responsible for the variations in the plotted distance. There are short data acquisition gaps on December 15 and 17. Credit: ESA/Solar Orbiter/SWA team & S. Grant (UCL)

So far, the best detection of the comet’s tail from Solar Orbiter has come from the Solar Wind Analyser (SWA) instrument suite. Its Heavy Ion Sensor (HIS) clearly measured atoms, ions, and even molecules that are attributable to the comet rather than the solar wind.

Ions are atoms or molecules that have been stripped of one or more electron and now carry a net positive electrical charge. SWA-HIS detected ions of oxygen, carbon, molecular nitrogen, and molecules of carbon monoxide, carbon dioxide and possibly water. “Because of their small charge, these ions are all clearly of cometary origin,” says Stefano Livi, Lead Investigator of SWA-HIS from Southwest Research Institute, Texas.

Solar Orbiter's View of Comet Leonard in Ultraviolet Annotated

A composite of Comet Leonard images captured December 15-16, 2021, in ultraviolet light by the Metis instrument onboard the ESA/NASA Solar Orbiter spacecraft. The comet transited across the field of view with its dust and ion tails pointing towards the instrument. Credit: ESA/Solar Orbiter/Metis Team

As a comet moves through space, it tends to drape the Sun’s magnetic field around it. This magnetic field is being carried by…



Read More:Solar Orbiter Spacecraft Catches a Second Comet by the Tail