A dazzling comet is approaching the Earth, with the potential to outshine even the brightest stars in the night sky. This incredible celestial object was first spotted in early 2023 when it was about 7.3 astronomical units away from our planet – for reference, that’s 7.3 times the average distance between the Earth and the Sun. Despite having an initial magnitude of 18, far too faint to be seen with the naked eye, the comet is now quickly approaching us. There’s a high likelihood that it will be the brightest comet visible to us in decades. So how did astronomers discover this comet? When will the comet reach its peak brightness? Finally, and most importantly, what is the one thing astronomers are concerned about in this comet?

We Have a Celestial Visitor

The celestial object we’re talking about was initially discovered on the night of 22nd February 2023 by ATLAS, a robotic early warning system in South Africa. ATLAS was explicitly designed to detect near-Earth asteroids in advance and warn us if there’s a possibility of impact. However, after astronomers calculated its trajectory, they discovered that the Purple Mountain Observatory in China, also known as Tsuchinshan, had already captured images of the object on 9th January 2023.

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C/2023 A3 (Tsuchinshan-ATLAS) as viewed through telescopes in Chile and Australia in February 2023. (Image credit: Filipp Romanov/Wikimedia Commons)

At first, the object was thought to be an asteroid, but subsequent observations from the Palomar Observatory in California revealed a dense coma and a short tail, indicating that it was, in fact, a comet. In keeping with the standard naming convention, the comet was named C/2023 A3 Tsuchinshan-ATLAS. 

What’s in the name?

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How the comet is named

The naming system for comets and asteroids follows a well-defined pattern. It begins with a prefix indicating the object type – in this case, C/  denotes a non-periodic comet that takes more than 200 years to orbit the Sun and may have an irregular orbit. The prefix is followed by the year of discovery – 2023 in this case – and a letter-number combination representing the time of discovery. Each month is divided into two halves, labeled alphabetically – A for the first half of January, B for the second half, C for the first half of February, and so on. The accompanying number signifies the order of discovery within that period. Lastly, the name of the observatory or telescope that discovered the object can also be added.

So C/2023 A3 Tsuchinshan-ATLAS is a non-periodic comet, the third object discovered in the first half of January 2023 by Tsuchinshan and ATLAS combined.

Based on its trajectory, comet “A3” is believed to have an orbital period of around 80,000 years, according to initial analysis. As of March 2023, the comet is located between the orbits of Jupiter and Saturn. It’s moving at a staggering pace of 290,664 km/hr or approximately 80.74 km/s relative to Earth.

Important Dates

As mentioned earlier, Comet A3 was discovered when it was roughly 1.1 billion km away from Earth. On September 27, 2024, it will make its closest approach to the Sun, known as perihelion, and come within 58 million km of the Sun, near Mercury’s orbit. This significant change in distance from the Sun typically causes a comet’s intrinsic luminosity to increase by 17 magnitudes. After perihelion, Comet A3 will pass relatively close to our planet, reaching its perigee on October 13, 2024.

The Problem with the Comet

The burning question on everyone’s mind is whether Comet A3 will meet our expectations or fall short like some of its predecessors. The answer to that question hinges on several factors, including the comet’s orbit, its position relative to the Earth and Sun, and its chemical composition. A3 originates from the Oort Cloud, a spherical shell of icy space debris that may contain trillions of objects, some as large as mountains.

The comet’s eccentricity indicates that it is traveling in a parabolic orbit, suggesting that it has never passed near the Sun before, which is not great news. This means that its surface is likely coated with highly volatile materials such as frozen nitrogen, carbon monoxide, and carbon dioxide. As this ice vaporizes far from the Sun, a distant comet can experience a brief surge in brightness, raising unrealistic expectations.

However, if recent calculations are correct, Tsuchinshan-ATLAS is traveling in an elliptical orbit, which means it is likely a long-term visitor to our solar system. In this case, any highly volatile materials on its surface would have already been shed, and its current level of activity represents its true nature.

The situation was similar with Comet Hale-Bopp, which was observed to be traveling in an elliptical orbit with a period of roughly 4,200 years when it was still far from the Sun. This suggested that it had visited our solar system multiple times before, and many astronomers anticipated its eventual evolution into a bright and spectacular object, which it did.

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Comet Hale-Bopp | Credits: E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria

Thankfully, while the “Oort cloud rule” generally holds true, there have been some exceptions in the past. One such case was the arrival of Comet Arend-Roland in the spring of 1957. Despite being a first-time visitor, it put on a stunning display, reaching a brightness of first magnitude and displaying a 30-degree tail, along with a 15-degree tail directed towards the Sun.

Another example is Comet McNaught, which traveled from the Oort Cloud and provided a spectacular show in January 2007. This comet produced a magnificently huge tail and became so bright that it was briefly visible during the daytime next to the Sun. These examples give us hope that Comet Tsuchinshan-ATLAS may still surprise us with an impressive display.

Observing the Comet

Currently, Comet A3 is so faint that it can only be seen through large telescopes, which is unlikely to change for several months. However, if the comet behaves as expected, it should become visible through small telescopes in the early summer of 2024. By late September of that year, it may even be visible to the naked eye or through binoculars as a pre-dawn object low in the east before sunrise. Whether or not it will have a tail at that point is still uncertain, as it depends on the age and activity level of the comet.

In early October 2024, Comet A3 will pass very close to the Sun from the perspective of Earth, and as a result, it will disappear from sight. Assuming the comet survives its close encounter with the Sun, it should reappear in the northern hemisphere sky after October 11 or 12, 2024. At this point, it will become visible after sunset and gradually move higher in the sky each evening, making it easier to observe.

If we are lucky, Comet A3 may become as bright as first or even zero magnitude, outshining most stars in the night sky. Nevertheless, predicting the behavior of comets is notoriously challenging, and it’s impossible to say for sure what will happen. So all we can do is patiently await the approach of this celestial visitor and observe its progress as it draws nearer to our planet.

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