IAS Gyan

Daily News Analysis


25th January, 2023 Science and Technology

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  • On Feb. 1, a bright-green comet named C/2022 E3 (ZTF) will make a close approach to Earth for the first time in 50,000 years.
  • Swooping within 26 million miles (42 million kilometers) of our planet, the comet will offer a rare night-sky spectacle last seen when modern humans shared our planet with Neanderthals.


  • A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail.
  • These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet.
  • Comet nuclei range from a few hundred meters to tens of kilometers across.
  • They are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit.
  • Short-period cometsoriginate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune
  • Long-period cometsare originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide

Note: The Oort cloud is a big, spherical region of outer space enveloping our sun, consisting of innumerable small objects, such as comets and asteroids. NASA terms it “the most distant region of our solar system” and “Home of the Comets”.

What is the ‘Green Comet’?

  • Some comets appear to glow green when ultraviolet sunlight vaporizes carbon molecules in the comet's head.


  • 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 they 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 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?

  • Coming under the category of long-period comets, which take more than 200 years to orbit the Sun, the green comet is not easily spotted.
  • With a highly elliptical orbit, the comet will head back to the Oort cloud and make its next appearance roughly 50,000 years later.