Ultra-rare green comet passes by Earth

by Xypher Pino

If you were under the darkest of skies between January 30 and February 2, you could have experienced a once-in-a-lifetime moment. C/2022 E3, or comet ZTF, passed by Earth and was as close as 26.4 million miles, which means that you could have seen the comet with your naked eye.

Astronomers state that the last time comet ZTF got this close to our planet was more than 50,000 years ago, when Earth was going through an Ice Age. They were able to figure this out based on the comet’s trajectory and through orbital determination, a method used to estimate the orbits of celestial bodies and objects in space. Astronomers also assume that the comet had been circling the sun, though the length of time is unknown as the sun’s heat could have changed the trajectory of the comet.

Other than the fact that this comet was last seen millenniums ago, what made it stand out was its bright green glow, or as NASA describes it: “a greenish coma, short broad dust tail, and long faint ion tail.” The reason why comet ZTF emits green is due to the presence of dicarbon – a reactive molecule that emits green light when it is met by sunlight. These molecules are also produced on Earth when hydrocarbons are burned, but it only lasts for a short period of time. If it were to be burned in an environment with extremely low temperature and pressure though, that green emission can last longer. Since space has zero air pressure and has temperatures of around -455 degrees Fahrenheit, the comet can constantly emit a green glow.

A close image of Comet ZTF, clearly showing its bright green glow (image courtesy of NASA).
A close image of Comet ZTF, clearly showing its bright green glow (image courtesy of NASA).

There is a lot of science involved with this comet. Unfortunately for us though, this was the final time that this particular comet will cross paths with Earth, as astronomers predict that the comet is no longer in orbit, meaning that it will never return to Earth. If the comet were to come back, generations living today will be long gone and humans would most likely be extinct, which just shows how rare this comet sighting really was.

If you missed this comet, do not worry, as an average of ten comets pass by Earth’s orbit, though you will need the aid of a telescope to be able to view these comets. There is less than a 1-in-10 chance that a comet can be visible with your plain eye, and Comet ZTF might be the last comet for a while that could be seen without the use of technology.


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