February 6, 2023

The comet reappears in the sky after 50,000 years. Why is it green

The newly discovered green comet will be visible to the naked eye for the first time in 50,000 years on Thursday (12/01), and over the next few weeks.

Called C/2022 E3 (ZTF), it’s a small, icy, rocky object, about a kilometer in diameter, that was discovered in March 2022 by the Zwicky Transient Facility (ZTF), which operates the Samuel-Oschin Telescope at Palomar Observatory, California.

It was initially detected when it passed through the orbit of Jupiter and will reach perihelion (the closest point to the sun) on Thursday, when it will be 166 million kilometers from the star.

The closest point to Earth, at a distance of 42 million kilometers, will be reached on February 1, according to astronomers who have studied the comet’s trajectory.

Why green?

A comet only acquires a tail as it approaches the sun.

The ice in its core passes directly from a solid to a gaseous state, releasing gases and dust, which creates a cloud around it – called an ice cloud. with the Or “hair” – which reflects sunlight. In this comet, due to its composition, it is very green.

And as we get closer to the sun, these particles are spread out over thousands of kilometers, “flyed out” by the solar wind. There is the long tail – which disappears as the comet moves away from our star. A of C/2022 e 3 (ZTF) bluish and tertiary.

This trail can be seen, initially in the Northern Hemisphere, when a comet approaches our planet. With the help of telescopes, it has already been recorded in detail.

Most likely, to the naked eye, the comet will look like a hazy star. The unusual green color is probably due to the presence of diatomic carbon in the coma.

It will shine in all its splendor when it approaches Earth, which is expected to happen on February 1st.

However, it will be less exciting than the much larger Hale-Bopp (1997) or Neowise (2020) comets.

best observation period

With good binoculars, or even with the naked eye, the comet can be seen at night, as long as the sky is clear and there is no light pollution.

In the Northern Hemisphere, the best observation period will be the weekend of January 21st and 22nd and the following week, when it passes through the constellations Ursa Minor and Ursa Major.

Then, it can be seen in the Southern Hemisphere, and has its best visibility in early February, before returning to the outer reaches of the solar system.

Since the Neanderthals

Astronomers calculate that the origin of the green comet is the Oort Cloud, a massive spherical structure of comets located about a light-year from the Sun, within its gravitational field.

All long-period comets, such as C/2022 E3 (ZTF), are thought to originate in the Oort Cloud, while short-period comets (less than 200 years old) originate in the Kuiper Belt.

C / 2022 E3 (ZTF) already visited the inner solar system about 50,000 years ago, in the Upper Paleolithic, when it also passed close to Earth, then inhabited by Neanderthals and early to turn down sapiens.

Some astronomers say it will return in another 50,000 years, while others say there’s a good chance it will be expelled from the solar system forever before then.

The orbit of this comet around the Sun is so long that it goes beyond the boundaries of the solar system. This explains why it took so long to return.

Scientists intend to monitor it to learn more about the formation of comets, especially with the help of the powerful James Webb telescope.

“We will observe it from all sides. It is not the comet of the century, but we are happy to be able to observe such comets every year or two, because we consider them remnants of the formation of the solar system,” explained scientist Nicolas Biver, from the Paris-PSL Observatory.

*With information from Marcella Duarte, from Uol Tilt