Agreen-hued comet from the outer solar system is set to
swing through Earth’s neighborhood in the coming days for the first time in
50,000 years.
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The comet has been steadily gaining brightness and will make
its closest approach on February 2, when it comes within 26.4 million miles of
the planet — 110 times the distance to the moon. From the Northern Hemisphere,
the comet is likely to be faintly visible to the naked eye.
What is the comet’s name?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 the orbit
of Jupiter and roughly 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-suited to discover such objects.
What are comets, and why is this one green?Comets are clumps of dust and frozen gases, sometimes
described by astronomers as “dirty snowballs.” Most are believed to originate
from the distant, icy reaches of the solar system where gravitational
agitations sometimes push them toward the sun — an interaction that transforms
them into gorgeous cosmic objects.
When they leave their deep freeze, the heat from the sun
erodes their surfaces, and they start spewing gases and dust until they host a
glowing core, known as the coma, and a flamelike tail that can stretch for
millions of miles.
“They’re alive,” said Laurence O’Rourke, an astronomer with
the European Space Agency. “When they’re far from the sun, they’re sleeping,
and when they get close to the sun, they wake up.”
“Even with relatively modest binoculars, the powdery, fuzzy or smoky character of the ‘star’ ought to make it clear it’s a comet.
C/2022 E3 (ZTF), for example, is now glowing 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?The brightness of comets can be unpredictable. When scientists
first discovered the object last year, they knew only that it had potential to
be visible from Earth.
“Because each comet is its own living being, you don’t know
how it’s going to react until it passes the sun,” O’Rourke said.
Comet C/2022 E3 (ZTF) made its closest approach to the sun
on January 12, and the comet is now steadily brightening as it swings toward
the Earth. While the comet won’t pass us until Feb. 2, it is already nearly
visible to the naked eye — an encouraging sign for viewing opportunities, said
Mike Kelley, an astronomer at the University of Maryland and the co-lead of the
solar system working group at the Zwicky Transient Facility.
Still, seeing the comet could “require dark skies and an
experienced observer,” Kelley said.
In addition, comets can always surprise us. Sometimes there
can be a big explosion of gas and dust, and the comet might get suddenly
brighter even after it has left the sun behind.
How do I spot the green comet?To catch the comet, look north.
On January 30, the comet will reside directly between the
Big Dipper’s “cup” and Polaris, the North Star. If you are accustomed to
finding the North Star by following the two stars on the end of the Big
Dipper’s cup, then you should be able to spot the comet. Simply scan that
imaginary line until you see a faint smudge.
If you are struggling, the comet might still be too faint or
there might be too much light pollution. Try with a pair of binoculars.
“It’s sort of like searching for some endangered species, and then it pops into view. … That really is a charmer of an experience.”
“Even with relatively modest binoculars, the powdery, fuzzy
or smoky character of the ‘star’ ought to make it clear it’s a comet,” said
E.C. Krupp, the director at Griffith Observatory in Los Angeles.
A telescope will help you spot the colors and finer details,
including the comet’s glowing coma and lengthy tail.
Either way, the hunt will be fun.
“It’s sort of like searching for some endangered species,
and then it pops into view,” Krupp said. “That really is a charmer of an
experience.”
Why are astronomers excited for this green comet?Comets are relics of the early solar system and may have
been responsible for seeding early Earth with the building blocks for life.
“It really is a situation where we most likely would not
exist without their existence,” O’Rourke said.
And yet we do not get many opportunities 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 across the globe will observe C/2022 E3
(ZTF) over the coming months.
“We’re looking for our solar system’s place in the
universe,” said Kelley, who will use the James Webb Space Telescope to observe
the comet at the end of February. He wants to better understand how our planet
formed in order to note the conditions that gave rise to life on Earth.
But Kelley and others have to work quickly. After a brief appearance
in the night sky, it is unclear where C/2022 E3 (ZTF) may go. Because these
objects are so loosely bound to our solar system, the sun’s gravitational
influence might force the comet to take another trip around our star — perhaps
not returning for another 50,000 years. Or the sun might fling the comet from
the solar system entirely.
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