Is the Next Comet Visible From Earth Doomed?

In just a few weeks, you will see a bright comet in the sky! Or won't you? Here's the truth about the much-talked-about comet C/2023 A3 (Tsuchinshan-ATLAS). Right now, from most locations, the comet is too close to the Sun to be visible. However, you can still track its location using the Sky Tonight app. Download the app to discover 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)
• The next comet visible from Earth: bottom line

When is the next comet?

If it survives, the next comet visible from Earth will be 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 why is its survival in doubt? On September 27, comet C/2023 A3 will reach its perihelion — the point in its orbit closest to the Sun. 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 say 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)

In the database of the Comet Observing Site (COBS), the last visual brightness estimate of C/2023 A3 was made on September 12, 2024 — it was about magnitude 5.5. The distance between the comet and the Sun was only 14°, which is very close to the Sun. For reference, the relatively optimal distance (elongation) is 25°, which the comet will reach on October 15, when it will be visible in the evening sky. Objects closer to the Sun must be very bright to be easily seen with the naked eye.

By the way, this is the first visual observation of C/2023 A3 in a month — the previous one was on August 12 (mag 8.2), when the comet was last at 25° from the Sun. Apparently, observers are so excited about C/2023 A3 (Tsuchinshan-ATLAS) that they're willing to search for the comet even under difficult conditions.

We'll see where the observers' efforts take us. Those in the Southern Hemisphere have a better chance of seeing the comet, as C/2023 A3 there is further from the Sun. In late September, the elongation of the comet Tsuchinshan-ATLAS will be 23°, and the comet will be much brighter than it was in early August, at around magnitude 2. From the Southern Hemisphere, C/2023 A3 (Tsuchinshan-ATLAS) rises above the horizon in the morning.

Space observatories also help to monitor objects near the Sun. NASA's STEREO-A (Solar Terrestrial Relations Observatory) is one of them. It orbits slightly in front of Earth and has the Heliospheric Imager, which can capture a portion of the sky from 7° to 42° east of the Sun. In August, Comet C/2023 A3 was in the camera's field of view, allowing astronomers to continuously monitor its condition. The comet showed no signs of breaking up and appeared to be stable.

The images from STEREO-A are low resolution, so it's difficult to make precise estimates. A rough estimate of the comet's brightness on August 18 was about magnitude 6, ±1 magnitude. If the comet continues to brighten at this rate, it could reach at least magnitude 1 by the second half of October. This would make it the brightest comet visible in the Northern Hemisphere in the last 27 years, barring any unexpected events.

In addition, the comet will be visible in the field of view of the solar observatory SOHO sometime in September and between October 7-11. This will also allow astronomers to check the comet's brightness and condition.

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).

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 is currently hidden in the Sun's light, making the observations difficult. 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. Let's wait patiently for October, and hopefully, we'll be able to witness this true astronomical gem!