50,000 years on, ‘green comet’ comes visiting again

Source: The post is based on the article “50,000 years on, ‘green comet’ comes visiting again” published in TOI on 30th January 2023

What is the News?

Comet C/2022 E3(ZTF), popularly known as the “green comet” which last visited Earth’s neighbourhood 50,000 years ago when the Neanderthals were still roaming its surface can now be viewed with a pair of binoculars from a dark location.

What is Green Comet or Comet C/2022 E3?

Green Comet is believed to have come from the Oort Cloud, a theorized vast sphere surrounding the Solar System that is home to mysterious icy objects.

The last time the green comet passed Earth was during the Upper Paleolithic period, when Neanderthals still roamed Earth i.e around 50,000 years ago.

Why is this comet green in colour?

Comets are frozen rocky or gas-filled objects that are remnants of the formation of the solar system. 

Just like other bodies in space, comets also have orbits. They are sometimes pulled in close to the sun because of the sun’s gravity acting on them. 

NASA explains that as comets orbit near the Sun, they heat up and spew gases and dust into a glowing head that can be larger than a planet. The remains of dust following this burning up, from a distance, look like a trail of light to humans on Earth. Comets, therefore, have often been seen giving out blue or whiteish light or even green.

In this case, the green glow is thought to arise from the presence of diatomic carbon – pairs of carbon atoms that are bound together – in the head of the comet. The molecule emits green light when excited by the ultraviolet rays in solar radiation.

Is the green comet rare?

Green comets are not easily spotted as they come under the category of long-period comets, which take more than 200 years to orbit the Sun.

With a highly elliptical orbit, the green comet will head back to the Oort cloud and make its next appearance roughly 50,000 years later. But given their orbits, it’s not unique for comets to reappear close to Earth only after many, many years.