It doesn't have the name recognition of Halley's Comet, but this enormous snowball zipping through space has fascinated at least one astronomer night after summer night for its shape-shifting tail.
Dan Bartlett, an astrophotographer based in east-central California, caught Comet Olbers zigzagging across the night sky this week. But each time he looks up through binoculars or his camera, the comet takes a different form.
"This is the first time we've been able to witness this creature's behavior with modern day technology," Bartlett told Mashable. "And what a creature this comet has been."
Comet experts say while the sharp kink in Olbers' tail may look strange to the average eye, the cause of its jagged appearance is a well-understood phenomenon.
Comets are enormous balls of ice, dust, and rock that formed in the outer solar system, left over from the early days of planet formation about 4.6 billion years ago, according to NASA. Their ice starts to disintegrate as they get closer to the sun, converting instantly from a solid to a gas, skipping over the liquid phase. That process creates their signature tails, millions-of-miles-long trails of debris.
Hundreds of years ago, people considered comets bad omens. Today, scientists know these icy bodies as time capsules of the ancient solar system. Some astronomers believe comets brought water and organic compounds — aka the building blocks of life — to early Earth.
Along with their trails of dust, comets also drag plasma, sometimes bluish in color, across the sky. The plasma tail, which looks a bit like Harry Potter's lightning bolt scar in Bartlett's photo, is composed of ionized gas molecules. These charged particles are easily influenced by changes in the sun's activity, said Henry Hsieh, a Planetary Science Institute researcher.
He compares the solar wind to a river constantly flowing away from the sun.
"The ion tail is basically caught up in that river," Hsieh told Mashable. "You see a straight tail most of the time, but then every so often, you'll have this bit of a hiccup in the sun — these coronal mass ejection events — where it'll just kind of send a particularly large or denser bunch of material outward."
Coronal mass ejections, or plasma spewed from the outer layer of the sun's atmosphere, involve enormous solar explosions. Through a solar telescope, the ejection looks like a fan of gas flying into space. NASA likens these ejections to cannonballs hurtling in a single direction, only affecting a targeted area.
"If this hits the comet, then it will cause a disruption to this nice flowing river," Hsieh said, "like a rock suddenly came loose, and the flow of the river suddenly got a little bit faster, but momentarily."
Right now the sun is near the height of its activity in the 11-year solar cycle, so its magnetic field is more chaotic. As the comet experiences these changes traveling through the inner solar system, the tail keeps trying to realign, resulting in these kinks and bends, said Tony Farnham, an astronomer at the University of Maryland.
"There are even occasions when the comet passes through a region where the magnetic field completely changes direction (called a sector boundary)," Farnham wrote in an email, "and the plasma tail will 'disconnect' from the comet, to be followed by the formation of a new tail over the next few days."
The comet, officially dubbed 13P / Olbers, is named after German astronomer Heinrich Olbers, who first observed it in 1815. The comet was last seen from Earth in 1956.
Comet Olbers' closest approach to the sun was on June 30, but it's now on its way back toward the so-called Oort Cloud on the outer edge of the solar system. Though the weirdly distorted tail is probably just the result of a lively comet reacting to the sun's wild behavior, little is known about this particular visitor to rule out something else inherently unusual about it.
This is essentially the first opportunity in contemporary times that astronomers have had to study the comet up close and during peak activity, Hsieh said. Astronomers will know more in the coming months as they complete their analyses.
"All comets are kind of like different beasts," he said. "They're all special, and that's what makes them fun to study."
