On Wednesday (Feb. 1) a comet that has not visited the Earth since the last ice age and the time of the Neanderthals will make its closest approach to our planet, or perigee.
Excitingly, the comet C/2022 E3 (ZTF), which last passed through the inner solar system around 50,000 years ago, will be at its brightest during this time and may even be visible to the naked eye under the right conditions. The comet should be observable for days as it approaches our planet and then recedes on its way to the outer solar system.
During the comet's perigee, it will come to within a distance of around 26 million miles (42 million kilometers) from our planet, which is equivalent to about 28% of the distance between Earth and the sun. If you've been waiting to get a look at C/2022 E3 (ZTF) before it speeds away, now is your best chance.
The comet is expected to become visible around 6:49pm EST on Wednesday, February 1, although it may be the most visible on Sunday, February 5, when it passes by the bright star Capella, or between February 9 and 13, when it will get some shine from Mars.
What makes this particular comet "green," or otherwise unique? From The Guardian:
It has been nicknamed "the green comet" because of its verdant glow, and is thought to have come from the Oort cloud – a collection of icy bodies that are believed to exist in the farthest-flung part of the solar system.
The green glow isn't unique to this comet, although it is an interesting feature. The phenomenon is thought to arise from an interaction between light from the sun and diatomic carbon. Diatomic carbon is an unstable, gaseous form of the element in which carbon atoms are bonded together in pairs. Scientists say it is formed on the head of the comet when larger carbon-based substances are broken down by sunlight as the comet approaches the sun.
When diatomic carbon is excited by ultraviolet rays, it gives off light, resulting in the green coma that has been seen surrounding the nucleus of the comet. However, ultraviolet light can also cause diatomic carbon to break down. This, experts say, explains why the tail of the comet is not green.
Green comet C/2022 E3 (ZTF) will be closest to Earth on Feb. 1. Here's how to see it. [Robert Lea / Space.com]
What is 'the green comet' and how can you see it? [Nicola Davis / The Guardian]