Green comet is caught in the photo

Astrophotographer Andrew McCarthy has published a very spectacular image of comet C/2022 E3 (ZTF). The last time it could be seen in the Earth’s sky 50 thousand years ago, when Neanderthals lived on our planet.

Comet C/2022 E3 (ZTF). Source: Andrew McCarthy

Comet ZTF was discovered in March 2022, when it was located at a distance of 643 million km from the Sun. Subsequent calculations showed that it moved in a very elongated orbit, which aphelion lying at a distance of 2800 au from the Sun (this is 70 times the distance to Pluto). Thus, the comet came to us from the Oort cloud. The last time ZTF visited the inner part of the Solar System was about 50 thousand years ago, at a time when Neanderthals still lived on Earth.

The tailed guest passed the perihelion of its orbit on January 12. Now its visible magnitude exceeds +6, which means that it can be seen with the naked eye under ideal observation conditions.

The image taken by Andrew McCarthy shows the extended tail and the coma surrounding the comet nucleus. The characteristic green color, apparently, is due to the presence of diatomic carbon molecules, also known as diacarbon. They are destroyed by the Sun (this process is called photodissociation), which is accompanied by radiation at a wavelength of 518 nm, corresponding to green light. Photodissociation destroys the carbon dioxide before it has time to move away from the nucleus. Therefore, the molecules do not have time to get into the tail of the comet and it does not turn green.

In the coming days, the brightness of ZTF may increase a little more. In time, this will coincide with the period of its optimal visibility. Now the comet is high in the sky (it should be searched for between the Ursa Major and Ursa Minor), visible throughout the night and at the same time, there is no bright Moon in the sky.

It is worth saying that with a high degree of probability, this is the last visit of comet ZTF. The influence of gravity of large planets changed its trajectory in such a way that it turned from a very elongated ellipse into an open hyperbola. So after the current passage through the central regions of the Solar System, comet ZTF is likely to leave it forever.

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