A
Green-hued comet that has been lurking in the night sky for months is expected
to be the most visible to stargazers this week as it gradually passes Earth for
the first time in about 50,000 years.
The
cosmic visitor will swing by our planet at a distance of about 26.4 million
miles (42.5 million km).
Here
is an explanation of comets in general and this one in particular.
WHAT
IS A COMET?
Nicknamed
"dirty snowballs" by astronomers, comets are balls of ice, dust and
rocks that typically hail from the ring of icy material called the Oort cloud
at our solar system's outer edge. One known comet actually originated outside
the solar system - 2I/Borisov.
Comets
are composed of a solid core of rock, ice and dust and are blanketed by a thin
and gassy atmosphere of more ice and dust, called a coma. They melt as they
approach the sun, releasing a stream of gas and dust blown from their surface
by solar radiation and plasma and forming a cloudy and outward-facing tail.
Comets
wander toward the inner solar system when various gravitational forces dislodge
them from the Oort cloud, becoming more visible as they venture closer to the
heat given off by the sun. Fewer than a dozen comets are discovered each year
by observatories around the world.
Related video: The Story Behind
a Once-in-a-Lifetime Green Comet That's About to Fly Past
Earth (Dailymotion)
This
comet last passed Earth at a time when Neanderthals still inhabited Eurasia,
our species was expanding its reach beyond Africa, big Ice Age mammals
including mammoths and saber-toothed cats roamed the landscape and northern
Africa was a wet, fertile and rainy place.
The
comet can provide clues about the primordial solar system because it formed
during the solar system's early stages, according to California Institute of
Technology physics professor Thomas Prince.
WHY
IS THE COMET 'C/2022 E3 (ZTF)' GREEN?
The
green comet, whose formal name is C/2022 E3 (ZTF), was discovered on March 2,
2022, by astronomers using the Zwicky Transient Facility telescope at Caltech's
Palomar Observatory in San Diego. Its greenish, emerald hue reflects the
comet's chemical composition - it is the result of a clash between sunlight and
carbon-based molecules in the comet's coma.
NASA
plans to observe the comet with its James Webb Space Telescope (JWST), which
could provide clues about the solar system's formation.
"We're
going to be looking for the fingerprints of given molecules that we can't
access from the ground," said planetary scientist Stefanie Milam of NASA's
Goddard Space Flight Center in Maryland. "Because JWST's so sensitive,
we're expecting new discoveries."
HOW
CAN ONE SEE GREEN COMET?
Using
binoculars during a clear night, the comet can be seen in the northern sky. On
Monday, it appeared between the Big Dipper and Polaris, the North Star. And on
Wednesday, it was positioned to appear near the constellation Camelopardalis,
bordered by Ursa Major, the Big Dipper and the Little Dipper.
Finding
a remote location to avoid light pollution in populated areas is key to
catching a nice view of the comet as it journeys past our planet heading away
from the sun and back toward the solar system's outer reaches.
