A green comet that has lurked in the night sky for months is expected to be the most visible to stargazers this week as it slowly passes Earth for the first time in nearly 50,000 years.
The cosmic visitor will swing by about 26.4 million miles (42.5 million km) from our planet.
Here’s 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 erupt from a ring of icy material called the Oort cloud at the outer edge of our solar system. 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 covered by a thin and gaseous 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 cloud and outward tail.
Comets drift toward the inner Solar System when various gravitational forces remove them from the Oort cloud, becoming more visible as they get closer to the heat given off by the Sun. Fewer than a dozen comets are discovered each year by observatories around the world.
This comet last passed Earth at a time when Neanderthals still lived in Eurasia, our species was expanding its reach beyond Africa, bringing large Ice Age mammals including mammoths and saber-toothed cats into the landscape and North Africa was a wet, fertile and rainy place.
According to California Institute of Technology physics professor Thomas Prince, the comet may provide clues about the early Solar System as it formed during the early stages of the Solar System.
Why is Comet ‘C/2022 E3 (ZTF)’ green in colour?
The green comet, which has the formal name 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 green, emerald color reflects the comet’s chemical composition—it’s the result of collisions 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 may provide clues about the formation of the Solar System.
“We’re going to be looking for fingerprints of given molecules that we can’t access from the ground,” said planetary scientist Stephanie Milam of NASA’s Goddard Space Flight Center in Maryland. “Because JWST is so sensitive, we are looking forward to new discoveries.”
How can one see the green comet?
The comet can be seen in the northern sky during a clear night using binoculars. On Monday it appeared between the Big Dipper and the North Star Polaris. And on Wednesday, it was positioned to appear near the Camelopardalis constellation, bordered by Ursa Major, the Big Dipper and the Little Dipper.
Finding a remote location that avoids light pollution in populated areas is key to catching a good view of the comet as it moves away from the Sun from our planet and toward the outer reaches of the Solar System.