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A green comet set to swing by Earth

Comet C/2022 E3 pays Earth a visit for the first time in 50,000 years

An aquamarine comet traversing through space on Jan. 27, 2023. The comet, C/2022 E3, is expected to be closet to the Earth in February. // Photo courtesy of Edu INAF

An out-of-this-world, brilliantly bright green comet is set to be visible from Earth this week for the first time in 50,000 years.

The comet, called C/2022 E3 (ZTF), is expected to be the closest to Earth on Feb. 1 but will still be visible in the following weeks. For those concerned about a potential apocalypse-level event, have no fear; the closest this comet will get is about 28 million miles away from Earth. 

C/2022 E3 was discovered in March 2022 by astronomers Bryce Bolin and Frank Masci at the Zwicky Transient Facility (ZTF). Names of comets are decided by the International Astronomical Union.

C/2022 E3 is from a region of space known as the Oort Cloud. According to Asmaa Boujibar, an assistant professor of planetary science at Western, there are two types of comets: short-period comets and long-period comets. 

Long-period comets, like C/2022 E3, typically come from far outside the solar system and can take thousands of years to orbit the sun. Short-period comets take under 200 years to orbit the sun and generally originate from the Kuiper Belt. Pluto is the most commonly recognized object residing in the Kuiper Belt. 

With an infinite number of objects in the universe, scientists have come up with a few ways to differentiate comets from other cosmic bodies. One key difference between a comet and an asteroid, for example, is that a comet has a tail.

“Sometimes they're called snowballs, dirty snowballs. Dirty because it's not just ice, but it's ice and dust,” Boujibar said, referring to comets. “Some of the ice blends, and that's what makes this giant tail … Comets usually have two tails. One tail is made of gas, and the other one is made of dust.” 

Comets' tails can be millions of miles long, and most are not visible to the naked eye, unlike the aquamarine comet that’s paying our planet a visit this week.

Bryce Bolin, one of the astronomers who discovered C/2022 E3 and a current NASA Postdoctoral Program Fellow, confirmed that C/2022 E3 was a comet based on the angle it was approaching from. 

“The dead giveaway that this is probably a comet was not necessarily visual appearance and images but by the direction it was coming from,” Bolin said. “If this thing was truly an asteroid, it would have been coming from the same direction as the planets and asteroids. And instead, the comet was coming from a 90-degree angle above the solar system.”

Bolin said even the origin of the words “comet” and “asteroid” have interesting backstories. The term “asteroid” was coined by German-born British astronomer William Herschel. It derives from the word “aster,” which means star in Latin. So, “asteroid” means an object has the appearance of a star. On the other hand, the word comet is Greek for “long-haired.” The “long hair” in this instance is the comet's tail. 

C/2022 E3 is unique from most comets because of its aquamarine tint. Comets turn green because they contain chemicals, such as diatomic carbon, that decay and emit a green appearance when they're energized by the sun's light, Bolin said.

The process for finding and naming C/2022 E3 may be different than some originally imagined. Bolin did not spend hours upon hours searching charts, pictures and graphs for a tiny green blip in the cosmos. Instead, he and other scientists created a machine that used artificial intelligence to seek out and identify comets based on preexisting data.

“We used real pictures of comets and we trained the AI to say, okay, if you see something else like this in the data, let us know,” Bolin said.

When the AI spotted C/2022 E3, Bolin recognized the significance of discovering a comet that last passed a much colder Earth. The last time C/2022 E3 was this close to our planet was during an ice age, said Jackie Caplan-Auerbach, an associate professor of geology at Western. She estimates that at that point, Bellingham was likely under about three kilometers of ice.

For observers hoping to spot the comet streaking across the sky, Bolin urges eager comet gazers to get away from any light pollution and look towards the north. 

“Coming up soon, in the next few days, it's gonna be kind of hard because the moon is waxing, it's getting brighter,” Bolin said. “The full moon I think is Feb. 5. But after that, the comet will still be pretty bright, and the sky will be darker. If you can, go out and see it if you go to a dark place. You might have to drive an hour or two, but if you bring a pair of binoculars, it's totally worth it.”

Mathew Callaghan

Mathew Callaghan (he/him) is a senior sports reporter for the Front this quarter. He plans to major in journalism and minor in law, diversity and justice through Fairhaven. In his free time, Mathew likes to write, hike, read and play basketball. 

You can reach him at

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