Rare green comet C/2022 E3 is about to make its closest pass by Earth

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A comet that last passed by Earth about 50,000 years ago is coming around again and will make its closest pass on 2 February, at which point it may be visible with the naked eye

Space 25 January 2023

By Leah Crane

A rare green comet is about to make its closest pass by Earth. The comet, called C/2022 E3, spends most of its time on the outermost edges of the solar system, in the Oort cloud, but it will make its closest pass by Earth on 2 February.

The close pass will bring the comet within about 45 million kilometres of Earth, about 120 times the distance between Earth and the moon or about one-fifth the average distance to Mars. It only orbits the sun once every 50,000 years or so, so its last pass by our home planet was in the Stone Age, when humans still coexisted with Neanderthals.

Those early humans may have been able to see C/2022 E3 in the sky, and it is expected to be possible with this pass too, in areas in the northern hemisphere with little light pollution. It is located near the constellation Boötes, just to the east of the Little Dipper, and on 1 and 2 February it might be visible with the naked eye. With a telescope, binoculars or a camera with the option for an extended exposure, it is expected to remain visible through the middle of the month before it slips away back towards the Oort cloud.

C/2022 E3 was first spotted by astronomers using the Zwicky Transient Facility in California in March 2022, when it came into the solar system past the orbit of Jupiter. Its coma, the cloud of gas surrounding the main body, or nucleus, of the comet, appears green because of carbon gas. It’s not just any carbon, though – it is a relatively rare type called diatomic carbon, which consists of two carbon atoms bound together.

Once the strange comet leaves Earth’s neighbourhood, some observations have hinted that it might be travelling fast enough that it will end up leaving the solar system altogether, or have its orbit bumped around by the gravity of the planets so that it won’t pass by again for millions of years. This may be the last chance to spot it.

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