Comet C/2023 A3 Survived Meeting With The Sun! Now What?

C/2023 A3 (Tsuchinshan-ATLAS) survived its close encounter with the Sun on September 27 and is now on its way to Earth. Is the comet safe now? Will it collide with Earth? We'll answer all your questions here! In the meantime, 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!

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 next comet visible from Earth is C/2023 A3 (Tsuchinshan-ATLAS). On October 12, it will pass closer to Earth than Venus (0.48 AU). Shortly before, it will become visible to the naked eye, and likely show a long, beautiful tail.

Observers in the Northern Hemisphere have extra reason to be excited! This comet will be prominently visible from northern latitudes. The last time a comet caused such excitement in this region was Hale-Bopp in 1997.

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℃.

At perihelion, the comet’s estimated brightness was about magnitude 2, so C/2023 A3 needs to brighten by only 1 magnitude to be more luminous than the famous C/2020 F3 (NEOWISE) 4 years ago.

The length of the comet's tail has already exceeded 7°, the equivalent of about 14 discs of the Full Moon. And this is the main dust tail, just one of three tails! There is also the gas tail and a secondary dust tail of large dust particles, 45° to the right of the main tail.

Now we don't have to worry about the comet disintegrating. The only question left is how bright the comet will be? We'll know in a few days.

Begin observations in early October. The comet is expected to reach peak brightness around October 9-12, although it will still be quite close to the Sun in our sky. The comet will be an evening object, so as soon as the Sun sets, find a suitable location and start looking for the comet. In the dedicated article, we explain in detail how and when to search for 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 will pass 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.

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 and has continued to brighten as it travels through the Solar System. The comet will put its best display around October 9-12, when it’s expected to be visible during the day. 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 -7 mag on October 28! Two bright comets in one month — what a treat for skywatchers!