A newly discovered comet may light up the sky in the fall of 2024, if we’re lucky.
But before focusing on our latest comet discoveries, I first want to mention that this month marks the 50th anniversary of comet discovery. Comet Kohoutek. If you are of a certain age, you might cringe a little at the mere mention of that specific celestial body.
As has often been said, the only predictable thing about comets is their unpredictability. When Comet Kohotek was discovered when it was still significantly farther from the Sun – close to Jupiter’s orbit (although nowhere near the planet itself) – the conclusion was that it was a giant among comets that would become extremely bright. Brightness predictions ranged down to -10 (as bright as a first or last quarter moon). Dr. Brian Marsden of the Central Bureau of Astronomical Telegrams announced that this could be the “comet of the century”. The mainstream media took him at his word and booed the approach of a comet so bright it might be visible in broad daylight. The world was ready to witness a glowing heavenly light show.
Related: Comets: everything you need to know about the ‘dirty snowballs’ of space
But Kohotek turned out to be pretty ordinary as naked-eye comets go and much less dim than the predictions originally suggested. Most people missed it completely, partly because of the light pollution and also because it was fairly low on the horizon. The recriminations were nasty with astronomers and the news media blaming each other and the public blaming both.
I decided to start with this sad saga, because after half a century on social media, I’m already starting to see announcements of a new comet that some are touting “could be bright in 2024”. Well… maybe you will, maybe you won’t.
It was first identified as an asteroid
The comet in question is C/2023 A3 (Tsuchinshan-ATLAS), which was detected by the Terrestrial Collision Last Warning System (ATLAS) in South Africa on February 22. ATLAS is an automated early warning system developed specifically to detect near-Earth asteroids a few weeks to days before they are likely to hit Earth.
Although originally an asteroid, it was later determined that the same object had been photographed six weeks earlier by the Purple Mountain Observatory (Tsuchinshan) in eastern Nanjing, China. Subsequently, it was imaged on December 22, by the Zwicky Transit Facility (ZTF) at Palomar Observatory. These images also revealed a highly condensed coma and a short tail which indicates that it is not an asteroid, but a comet.
Will it sizzle or fade out?
When first discovered in the constellation Serpens, Comet Tsuchinshan-Atlas was an extremely faint (magnitude 18) object 680 million miles (1.09 billion km) from the sun. But when it reaches its closest point to the Sun (perihelion) on September 27, 2024, that distance will have shrunk to 36 million miles (near Mercury’s orbit). Such a massive change in solar distance would normally cause a comet to increase its intrinsic luminosity by 17 magnitude. Moreover, Tsuchinshan-ATLAS will pass moderately close to Earth about two weeks after perihelion.
But will this comet really turn out to be a celestial masterpiece or will it end up like it was Kohotek in 1973-74? The inability to predict how a comet will appear or how bright it will be is not surprising to those who study these mystical objects. What we will eventually see depends on many variables – the comet’s orbit, the relative positions of the comet, Earth and the Sun, and of course the size and composition of that icy clump of solar system rubble that makes up the comet’s nucleus, and usually just a few. kilometers across. Its earthy, rocky, and frozen matter is no different from that of Saturn’s rings.
Possible bright future
Astronomers have developed general formulas and models for measuring the brightness of comets based on the observed behaviors of literally hundreds of them over a century. But comets, like humans, have their individual quirks.
If Comet Tsuchinshan-ATLAS lives up to its most optimistic predictions, it should make its best show in 2024, between October 12 — when it passes near Earth at a distance of 44 million miles (71 million km) — and October 2020. 19, when it appears low in the western and southwestern evening sky 1 to 3 hours after sunset. During this time frame, it can appear as bright as the first or second star and may also show a significant tail despite the low altitude and bright moonlight (unfortunately the full moon occurred on October 17th).
So let me stress here that there is a lot of “potential” that Tsuchinshan-ATLAS could evolve into a bright comet. However, there is a major stumbling block for this to happen.
Most likely useless
Unfortunately, it seems more likely that Tsuchinshan-ATLAS, like Kohoutek and other comets of similar proportions (Cunningham in 1940-41, Austin in 1990 and ISON in 2013), may eventually fade away, because it is a “new” comet coming out of the Oort cloudThe spherical crust that surrounds the rest of the solar system consists of chunks of icy space debris that are as big as mountains. The Oort Cloud could contain billions or even trillions of objects.
The latest orbital calculations show that Tsuchinshan-ATLAS has an eccentricity of 1.0002280, which means it is traveling in a parabolic orbit, emerging directly from the Oort cloud. Therefore, it had never passed close to the Sun before. And this is bad news.
If the characteristics exhibited by other “Oort comets” also apply to Tsuchinshan-ATLAS, their surface is likely covered in highly volatile materials such as frozen nitrogen, carbon monoxide and carbon dioxide. Such ices evaporate away from the sun, giving a distant comet a short-term spike in brightness that in turn raises unrealistic expectations.
Already done “around the block”
On the other hand, if recent calculations show that Tsuchinshan-ATLAS has been traveling in an elliptical orbit and returning to the Sun from the distant past, then its shell of highly volatile material has already worn off, and what we are seeing now is the true fundamental level of activity. When Comet Hale-Bopp was still very far from the Sun, orbital data showed that it had been traveling in an elliptical orbit for about 4,200 years.
In other words, he’s been here before, maybe more than a few times. This is why many astronomers confidently predicted, nearly two years ago, that Hale-Bopp would eventually evolve into a bright, brilliant object.
Unfortunately, we can’t be too sure of Tsuchinshan-ATLAS.
Exceptions to the rule
Fortunately, the “Oort cloud base” is not absolute. There were exceptions. In the spring of 1957, the first-timer Arend-Roland comet turned out to be quite spectacular, becoming as bright as the first magnitude and shedding a tail of 30 degrees in length, plus it also produced a sun-directed tail measuring 15 degrees in length.
Another comet has traveled from the Oort cloud and put on a great show The culprit was McNutt In January 2007. We will remember her for a long time not only because she so wonderfully opens a huge tail, but also because she became so bright as To be briefly visible during the day by the Sun.
So there may still be hope for comet Tsuchinshan-ATLAS.
Late July 2024: “The Wall”
For now, astronomers can only sit back and quietly watch the comet’s progression as it slowly approaches the Sun and Earth. But when will we know for sure that it will become a masterpiece or just another faint, mysterious comet?
The phrase “hit a wall” means to encounter an obstacle that prevents progress. In the past, Oort comets that have shown an encouraging progression in terms of brightness have seen their steady brightness suddenly slow after crossing the orbit of Mars. Like a celestial marathon runner, it’s like a comet hitting a wall.
As far as the Tsuchinshan-ATLAS comet is concerned, it will not reach that point in its orbit until late July of 2024. If according to formulas and models the comet has brightened up to that point in time, it should then be bright at about 8 degrees and easily visible in Good binoculars and small telescopes.
If it then continues to brighten steadily after that time, there is a good chance that it will develop into an eye-catching spectacle. But if its bright trend suddenly slows, or even stops, all bets on a good show are off.
So, here is the story. Until then, all we can do is wait and watch.
If you want to check out Comet Tsuchinshan-ATLAS next year, our guides to the best telescopes and best binoculars are a great place to start. And if you’re looking to take pictures of the starry night sky, check out our how-to guide to photographing the moon with recommendations of the best cameras for astrophotography and the best lenses for astrophotography.
Joe Rao is a teacher and guest lecturer in New York Hayden Planetarium (Opens in a new tab). He writes about astronomy for Natural History Journal (Opens in a new tab)the Farmers’ almanac (Opens in a new tab) and other publications. Follow us on Twitter @employee (Opens in a new tab) and on Facebook (Opens in a new tab).
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