A green comet from the outer solar system will be moving through Earth’s neighborhood in the coming days for the first time in 50,000 years.
The comet has been steadily brightening and will make its closest approach on February 2, when it is 26.4 million miles from the planet, 110 times the distance to the moon. From the northern hemisphere, the comet is likely to be barely visible to the naked eye.
But you don’t have to wait until February to see this visitor. The coming weekend may offer favorable viewing opportunities with a pair of binoculars as the new moon creates darker skies.
What is the name of the comet?
The comet is known as C/2022 E3 (ZTF) because astronomers discovered it in March 2022 using a telescope on Palomar Mountain in California called the Zwicky Transient Facility (or ZTF).
At the time, the cosmic interloper was just inside Jupiter’s orbit and about 25,000 times dimmer than the faintest star visible to the naked eye. But ZTF, with a camera that has a wide field of view, scans the entire visible sky each night and is well prepared to discover such objects.
What are comets and why is this one green?
Comets are frozen collections of dust and gases, sometimes described by astronomers as “dirty snowballs.” Most are thought to originate in the distant, icy reaches of the solar system, where gravitational upheavals sometimes pull them toward the sun, an interaction that transforms them into magnificent cosmic objects.
When they emerge from their deep freeze, their surfaces are eroded by heat from the sun and they begin spewing gases and dust until they are home to a glowing core, known as a coma, and a flame-like tail that can extend for millions of miles.
“They are alive,” said Laurence O’Rourke, an astronomer with the European Space Agency. “When they are far from the sun, they are sleeping, and when they get closer to the sun, they wake up.”
C/2022 E3 (ZTF), for example, now glows green because ultraviolet radiation from the sun is absorbed by a molecule in the comet called diatomic carbon, that is, two carbon atoms fused together. The reaction emits green light.
How bright will this comet be?
Comet brightness can be unpredictable. When scientists first discovered the object last year, they only knew that it had the potential to be visible from Earth.
“Because each comet is its own living thing, you don’t know how it’s going to react until the sun goes by,” Dr. O’Rourke said.
Comet C/2022 E3 (ZTF) made its closest approach to the sun on January 12, and the comet is now shining steadily as it turns toward Earth. While the comet won’t pass us until February 2, it’s already nearly visible to the naked eye, an encouraging sign for observing opportunities, said Mike Kelley, a University of Maryland astronomer and solar system co-director. working group at the Zwicky transitional facility.
Still, seeing the comet could “require dark skies and an experienced observer,” Dr. Kelly said.
Also, comets can always surprise us. Sometimes there can be a huge explosion of gas and dust, and the comet can suddenly become brighter even after it has left the sun behind.
How can I see the green comet?
To catch the comet, face north.
On January 21, the night of the new moon and therefore of the darkest skies, the comet will be close to Draco, the dragon-shaped constellation that straddles Ursa Major and Ursa Minor.
During the following nights, the comet will trail along the dragon’s tail. And on January 30, the comet will reside directly between the “cup” of the Big Dipper and Polaris, the North Star. If you are used to finding North Star by following the two stars at the top of the Big Dipper’s cup, then you should be able to spot the comet. Just scan that imaginary line until you see a faint spot.
If you’re having difficulty, the comet may still be too faint, or there may be too much light pollution. Try a pair of binoculars.
“Even with relatively modest binoculars, the dusty, fuzzy, or smoky character of the ‘star’ should make it clear that it is a comet,” said EC Krupp, director of the Griffith Observatory in Los Angeles.
A telescope will help you spot colors and finer details, including the comet’s bright coma and long tail.
For anyone living above the 35th parallel, imagine a curved east-west line running from North Carolina through the Texas Panhandle to southern California, the comet will be visible all night starting January 22. But it’s relatively low on the horizon in the early evening, and it might be better to look for the comet later at night or even early in the morning when the comet is bobbing higher in the sky.
Dr. Krupp recommends looking at this weekend when the phase of the moon is new and therefore won’t cast a glow across the sky. But the comet will get brighter as it gets closer to Earth and easier to spot towards the end of the month. If you wait until then, you might want to try it in the early morning after the moon has set.
Either way, the hunt will be fun.
“It’s kind of like looking for an endangered species, and then it comes into view,” Dr. Krupp said. “That’s really a lovely experience.”
Why are astronomers excited about this green comet?
Comets are relics of the early solar system and may have been responsible for seeding the early Earth with the building blocks for life.
“It really is a situation where we most likely wouldn’t exist without it,” said Dr. O’Rourke.
And yet we don’t get much opportunity to study these objects, given that only a few each year are bright enough to be seen with the naked eye. As such, cometary astronomers around the world will be observing C/2022 E3 (ZTF) in the coming months.
“We’re looking for our solar system’s place in the universe,” said Dr. Kelley, who will use the James Webb Space Telescope to observe the comet in late February. He wants to better understand how our planet formed in order to look at the conditions that gave rise to life on Earth.
But Dr. Kelley and others have to work fast. After a brief appearance in the night sky, it is unclear where C/2022 E3 (ZTF) may go. Because these objects are so loosely tied to our solar system, the sun’s gravitational influence could force the comet to make another trip around our star, perhaps not returning for another 50,000 years. Or the sun could drive the comet out of the solar system entirely.