Comet Tsuchinshan-ATLAS Survived! Now What?

C/2023 A3 (Tsuchinshan-ATLAS) survived its close encounter with the Sun on September 27 and successfully passed the closest point to Earth on October 12. The comet has reached naked-eye visibility and will now entertain observers for some time. You can track the location of C/2023 A3 using the Star Walk 2 app. Download the app to find out where the comet is in the sky! Read on to learn what to expect from the comet.

Contents

• When is the next comet?
• Is the comet C/2023 A3 (Tsuchinshan-ATLAS) disintegrating?
• Last and future observations of C/2023 A3 (Tsuchinshan-ATLAS)
• Will Comet Tsuchinshan-ATLAS collide with the Earth?
• The next comet visible from Earth: bottom line

When is the next comet?

The comet currently visible from Earth is C/2023 A3 (Tsuchinshan-ATLAS). On October 12, it passed close to Earth (0.47 AU). Shortly before, it became visible to the naked eye and showed a long, beautiful tail. Sometime after, it even developed an anti-tail — a bright streak that appears to be pointing toward the Sun, opposite the other tails.

But the survival of the Comet Tsuchinshan-ATLAS was in doubt. On September 27, comet C/2023 A3 passed its perihelion — the point in its orbit closest to the Sun. It was thought that at a distance of 0.39 AU, C/2023 A3 may not be able to withstand the Sun's heat and could disintegrate, as Comet ISON did in 2013.

Adding to the concern, news surfaced in July 2024 that C/2023 A3 may be "doomed". Here is what astronomers said about the comet's prospects.

Is the comet C/2023 A3 (Tsuchinshan-ATLAS) disintegrating?

In early July, astronomy enthusiasts received some disappointing news. Zdenek Sekanina, a Czech-American astronomer and comet expert at NASA's Jet Propulsion Laboratory, published an article stating that the end of Comet Tsuchinshan-ATLAS is inevitable. He argued that the comet is showing signs of fragmentation, primarily indicated by a sudden cessation of its brightness increase and even a decrease in its brightness.

But is this really the case? In response to Sekanina's article, other astronomers offered their perspectives. They pointed out that Sekanina did not consider the comet’s phase angle — the angle between the incident light on the comet and the light reflected from the comet to an observer on Earth.

This phase angle significantly impacts the comet's brightness. When the comet is in opposition to the Sun (at 180° from the Sun, with the Earth on the same line), the phase angle becomes very small, and the comet's surface reflectivity sharply increases.

In the middle of April 2024, the comet was in opposition to the Sun, causing its brightness to sharply increase. Additionally, the comet's tail, pushed back by the solar wind, was projected behind the comet's “head”, further enhancing its brightness.

Then, the phase angle began to increase, greatly reducing the reflectivity of the comet's coma surface. Moreover, the tail was no longer projected onto the comet's head, so it no longer contributed to the comet's brightness.

Ignoring these factors might lead one to conclude that the sharp drop in the comet's brightness is due to the collapse of the nucleus. However, this is not the case. Recent Images taken three weeks after Sekanina's publication show no sign of the comet disintegrating. On the contrary, at 1.5 AU from the Sun, the comet shows large, well-developed dust and gas tails, as well as a large green fluorescent coma. Current estimates put the comet's brightness at 9.0 magnitude, slightly ahead of forecasts, suggesting that it may become even brighter than predicted.

To find out the likelihood of a comet breaking up near the Sun, we use the Bortle survival limit. The comet's absolute magnitude (H) must be brighter (i.e., the number must be smaller) than 7 + 6*q, where q is the minimum distance from a comet to the Sun. If H < 7 + 6 * q, a comet is likely to survive its perihelion passage.

The diameter of C/2023 A3’s nucleus is estimated to be about 1-2 km (meaning H = 4.5), and the minimum distance from the Sun is 0.4 AU. Thus, we get: 4.5 < 7 + 6 * 0.4 = 9.4

As we can see, the condition is met by a large margin, indicating that C/2023 A3 (Tsuchinshan-ATLAS) should not disintegrate.

Last and future observations of C/2023 A3 (Tsuchinshan-ATLAS)

On September 28-29, after the perihelion date, new confirmed observations appeared on the Comet Observing Site (COBS). It means that the positive predictions came true and comet C/2023 A3 (Tsuchinshan-ATLAS) successfully passed perihelion! It passed as close as 59 million km from the Sun and its nucleus heated up to 250℃.

We can now breathe a sigh of relief — no need to worry about the comet disintegrating (unlike the other potentially bright comet in October 2024)! The big question is how long will it stay visible to the naked eye? If all goes well, Comet C/2023 A3 (Tsuchinshan-ATLAS) should remain bright enough until around October 20, so don’t miss your chance to see it!

Right now, observers in the Northern Hemisphere are sharing their evening views of the comet. You can easily locate it in the west shortly after sunset if you know where to look. To track it quickly, use the Star Walk 2 astronomy app and watch a 30-second video on the easiest way to track the comet.

For more details, check out our article on how and when to observe Comet C/2023 A3 (Tsuchinshan-ATLAS).

Will Comet Tsuchinshan-ATLAS collide with the Earth?

We know that all big comets create an apocalyptic mood, and we're here to debunk the weird rumors: fortunately, no, C/2023 A3 (Tsuchinshan-ATLAS) will not collide with the Earth. On 12 October, it passed its closest point to us — at a distance of 71 million km or 0.47 AU. Even Venus comes closer to our planet: its closest distance to the Earth is about 38 million km or 0.25 AU. After that, C/2023 A3 continued its journey through the Solar System, moving further and further away from our planet. For the next 20 years, the comet will move toward the edge of the Solar System and will not return for another 80,660 years.

Check out our article on asteroids predicted to hit our planet if you're interested in the space objects that can collide with Earth.

The next comet visible from Earth: bottom line

Despite all the concerns, Comet C/2023 A3 appears to be doing well — it shows no signs of disintegration. The comet reached its maximum brightness on October 12 and continues to delight observers by remaining visible to the naked eye. The easiest way to track its position in the sky is to use an astronomy app. Stay tuned for the latest news and predictions on Comet Tsuchinshan-ATLAS in our regularly updated article.

Another comet that definitely deserves your attention is the newly discovered C/2024 S1 (ATLAS). This sungrazer comet could be as bright as -3.3 mag on October 28! Two bright comets in one month — what a treat for skywatchers!