After 80,000 years visible again: what makes comet “C/2023 A3” so special?
This weekend it is most likely to see comet C/2023 A3 (Tsuchinshan-ATLAS). Last week, the Netherlands fell under the spell of the comet, which will be visible on the horizon until the end of November. According to UvA astronomer Alex de Koter, it is one of the most extraordinary celestial phenomena we can observe with the naked eye.
The fact that this comet is visible once every eighty thousand years already makes it a rare natural phenomenon. What else makes C/2023 A3 (Tsuchinshan-ATLAS) so special?
“In the first place, this comet comes from the Oort cloud, a giant cloud of ice-like objects that dates to the birth of our solar system. And this cloud is at a huge distance from the sun, far beyond the known planets and even beyond the Kuiper belt (where Pluto and other dwarf planets are located). The Oort cloud is extremely rich in comets. Because it is so far away, these comets take thousands to hundreds of thousands of years to travel to the inner solar system, which makes this observation so special.”
“In addition, the comet’s orbit is about 70 million kilometres away from Earth. That’s about half the distance between Earth and the sun. Its relatively short distance and its highly developed cometary tail, makes it one of the brightest and more visible comets of recent decades.”
The name, C/2023 A3 Tsuchinshan-ATLAS, is rather cryptic. Where did it come from?
“You have to think of that name as the comet's registration code. That follows an internationally standardised system within astronomy. The ‘C’ refers to ‘comet’, ‘2023’ refers to the year of discovery and ‘A3’ indicates that this is the third comet discovered in the first half of January (code for ‘A’ ed.). The name ‘Tsuchinshan-ATLAS’ refers to the two observatories that first observed the comet: the observatory in Tsuchinshan, China, and the ATLAS (Asteroid Terrestrial-impact Last Alert System) project in South Africa.”
‘Falling stars’ shoot through our atmosphere like in an instance. If you are not attentive, you will miss this fenomena. Why is the comet visible for such a long time and so clearly?
“Comets are balls of space debris mixed with ice, typically a few kilometres in diameter. C/2023 A3 (Tsuchinshan-ATLAS) has a diameter of about three kilometres. As they get close to the sun, the ice evaporates and space debris crumbles from the surface. This creates a glowing, hazy cloud around the comet nucleus, called the coma, and a long tail that can stretch for tens of millions of kilometres. Due to its enormous distance from Earth, you can sometimes see it visible in the sky for days to weeks. Eventually, after lots of orbits around the sun, such a comet disintegrates. The debris spreads all over its orbit. And sometimes the Earth passes through the orbit of such a crumbled comet. Small pieces of grit, millimetres or centimetres in size, then burn up in the Earth's atmosphere. We call their brief trails of light in the sky ‘shooting stars’.”
Amsterdam has a lot of light pollution. Will the comet be easy to see from here?
“I tried it last night, but it was far too cloudy. To see it, you need a clear view towards the horizon. In Amsterdam, there are few places where this is possible, so it's better to stand on a high building somewhere in the city. But a spot outside the city, say in the polder or on the beach, will offer much better conditions for observing the comet. Should you still want to try it, do so in the next few days. It really is one of the most extraordinary celestial phenomena we can see with the naked eye. At about eight in the evening, look in the direction from which the sun has set.”
What makes this phenomenon so special for astronomers?
“For astronomers, comets like these are fascinating research objects. The Oort cloud comets formed 4.5 billion years ago and then quickly ejected from the solar system through interaction with proto-planets (a pre-stage of a planet ed.). So, by analysing the comet's composition with telescopes, scientists can learn more the formation of planets and primitive molecules that also became trapped in their icy material. Nothing happened to them ever since; they have been in ‘the deep freeze’, so to speak, all that time. Now that C/2023 A3 (Tsuchinshan-ATLAS) has fallen towards the interior of the solar system, the material is thawing, revealing what the original grit particles - tiny pieces of stony material - looked like.”
