What 2024’s Bright Comet May Reveal About the Age of the Solar System

by Dr. Danny R. Faulkner on January 17, 2025
Featured in Answers in Depth

Comet Tsuchinshan–ATLAS

The brightest comet in years graced the evening sky in October 2024. The official name of the comet is C/2023 A3 (Tsuchinshan–ATLAS). A comet’s name reveals some things about the comet. The leading letter C in this designation indicates that this is a long-period comet (period > 200 years). The next part of the name means that it was the third comet discovered in the first half of January 2023. Tsuchinshan is the name of the Chinese observatory that first spotted the comet, and ATLAS refers to an observatory in South Africa that recorded the second discovery (nearly simultaneous discoveries of comets are co-credited to the discoverers). In general parlance, this comet is simply called Comet Tsuchinshan–ATLAS.

Comet Tsuchinshan–ATLAS brightened remarkably as it approached perihelion (closest approach to the sun) on September 27, 2024. Comets are brightest shortly after perihelion, but Comet Tsuchinshan–ATLAS was in conjunction with the sun (appearing closest to the sun) in early October, rendering it very difficult to see the comet from earth during this time. After conjunction with the sun, Comet Tsuchinshan–ATLAS began to emerge into the evening sky with reports of it being the brightest comet in years, but twilight prevented most people from seeing the comet when it was at its brightest. As a comet recedes from the sun, it rapidly fades. Each evening, Comet Tsuchinshan–ATLAS was higher in the sky and hence in a darker sky, but each evening, the comet was intrinsically fainter. By the second week of October, Comet Tsuchinshan–ATLAS was visible to the naked eye.

I wished to photograph Comet Tsuchinshan–ATLAS, but cloudy weather prevented me from seeing it until the evening of Thursday, October 17. During early twilight, I was able to spot the comet with binoculars, but as the sky got darker, I could see it without optical aid. Unfortunately, that night the moon was full (hunter’s moon) with the moon rising at sunset. That meant that as the sky began to darken, the sky was brightly lit by the very bright moon, greatly reducing the contrast of the diffuse comet tail. The comet would have been much more impressive if not for the light of the full moon. I took photographs that evening, as well as on the evenings of October 19 and 20, when the waxing gibbous moon was fainter, and the moon rose closer to the end of twilight. Thus, the sky background was darker, but I took those photographs where I live near the Creation Museum in Northern Kentucky with light pollution from greater Cincinnati. While these photographs were adequate, they would have been much better if the sky were darker. On the evening of October 21, I photographed the comet in Red River Gorge, a relatively dark site in eastern Kentucky, a two-hour drive from Northern Kentucky. The location was Chimney Top, a hoodoo in the gorge that has good exposure in all directions. The waning gibbous moon did not rise until long after twilight ended when the comet was still relatively high in the sky.

I took the first photograph with my Nikon D3300 camera with a 36 mm f/4.8 lens. The ISO was 6400, and the exposure time was 10 seconds. This is a narrow-angle view in which the comet appears largest. I took the second photograph with my Nikon D5600 camera with a 14 mm f/2.8 lens. The ISO was 6400, and the exposure time was six seconds. This is a much wider-angle lens. Comparing the two photographs, one can identify in the second photograph many of the stars in the first photograph. This indicates the difference in scale between the two photographs. I estimate the angular length of the tail in the second photograph to be more than a dozen degrees. At one point, the tail was measured to be 18 million miles (Rao 2024). That is 1/5 the distance between the sun and the earth. However, Comet Tsuchinshan–ATLAS rapidly faded, and I was able to see it with the naked eye for a little more than a week.

  • Tsuchinishan Atlas Comet
  • Tsuchinishan Atlas Comet

What Comets May Reveal About the Age of the Solar System

Creationists have long used the existence of comets as an argument for the recent origin of the solar system.

Creationists have long used the existence of comets as an argument for the recent origin of the solar system. The argument is that comets are relatively short-lived phenomena, with a maximum age far less than the supposed 4.5 billion years of the solar system. This problem has long been recognized by astronomers, which is why 75 years ago Jan Oort proposed his comet cloud as the solution to this problem. The Oort cloud supposedly is a large number of comet nuclei orbiting far from the sun, remaining in a sort of cold storage until an occasional passing star or other object redirects them toward the sun and inner solar system. That way, as comets die, they are continually resupplied from the Oort cloud. Never mind that there is no direct evidence of the Oort cloud’s existence.

Over the years, many articles about comets have appeared in creationary literature. I’ve even written a few articles about comets. For instance, more than 25 years ago, I wrote my most technical article on what comets reveal about the age of the solar system (Faulkner 1997). Summing up some of the information there, three mechanisms destroy comets:

  1. Large loss of mass each return to perihelion
  2. Collisions with planets
  3. Gravitational perturbations of planets

Comet Tsuchinshan–ATLAS is related to the third mechanism. There were over a thousand precise pre-perihelion measurements of the changing position of Comet Tsuchinshan–ATLAS that spanned more than a year. This allowed accurate calculation of the orbit the comet was following as it approached the sun. Astronomers use the astronomical unit (AU) to measure distances in the solar system. The AU is the average distance between the earth and sun (93 million miles = 150 million kilometers). At perihelion, Comet Tsuchinshan–ATLAS was 0.39 AU from the sun, but its aphelion (greatest distance from the sun) was approximately 307,000 AU from the sun (Giorgini n.d.). The defined size of an orbit (semimajor axis) is the average of the perihelion and aphelion distances. Therefore, the incoming orbit of Comet Tsuchinshan–ATLAS had a semimajor axis of 154,000 AU.

As long-period comets approach and leave the sun, they must pass through the part of the solar system where the planets are. As comets pass through the realm of the planets, the planets’ gravity produce small tugs on comets that we call perturbations. Perturbations either add orbital energy to comets or rob comets of orbital energy, with about an equal probability of either outcome for any given comet. If a comet’s orbital energy increases, the comet’s semimajor axis increases, while an energy decrease produces a smaller semimajor axis. Because these perturbations take place near perihelion, the perihelion distance is changed very little, so any orbital changes result in large changes in aphelion distances. Comet Tsuchinshan–ATLAS experienced a decrease in orbital energy, so its outgoing semimajor axis is 17,100 AU sun, with an aphelion of 34,200 AU. Consequently, the period of Comet Tsuchinshan–ATLAS shortened from 114 million years to 2.23 million years. In 1973–74, Comet Kohoutek had a similar reduction in orbital size and period: its incoming semimajor axis was 98,000 AU, its outgoing semimajor axis was 3,700 AU, and its period reduced from 11 million years to 78,000 years.

Periodic comets have orbits that are elliptical, with eccentricities between zero and one (long-period comets have eccentricities that are very close to one). A parabolic orbit has an eccentricity equal to one, but comets with eccentricities greater than one are hyperbolic. Both parabolic and hyperbolic comets are not bound to the solar system, so they cannot return to the sun. Sometimes it is difficult to tell whether a comet’s orbit is truly parabolic or just a very high eccentricity ellipse. Long-period comets are loosely bound to the solar system, so a slight increase in orbital energy results in ejection from the solar system, never to return. A good example of this was C/1980 E1 (Bowell) (Blos 2022). This comet had an inbound aphelion distance of 75,000 AU and a period of 7.2 million years, but its outgoing orbital eccentricity was 1.054, so the comet is no longer bound to the sun and will never return to perihelion. There are other examples of ejected comets, but Comet Bowell had the greatest outgoing eccentricity of any comet so far. As a side note, there have been two observed interstellar objects pass through the solar system, ‘Oumuamua (A/2017 U1) and 2I/Borisov (aka C/2019 Q4 (Borisov). These objects had both incoming and outgoing hyperbolic orbits.

When a comet is ejected from the solar system, it is a catastrophic loss. During its recent trek through the inner solar system, Comet Tsuchinshan–ATLAS was not lost to the sun, but its greatly shortened period means that it will return to perihelion much sooner than it would have had its orbit not been so drastically shortened. That means all three comet loss mechanisms are likely to operate on Comet Tsuchinshan–ATLAS sooner on future trips to perihelion, greatly accelerating the likely loss of Comet Tsuchinshan–ATLAS during a later perihelion passage. One must ask how many times in the past Comet Tsuchinshan–ATLAS has come to perihelion and how long it has avoided drastic changes to its orbital period as it recently has experienced. If the solar system has existed for 4.5 billion years, then Comet Tsuchinshan–ATLAS would have come to perihelion 40 times already. But this would be a gross underestimate of the number of returns. It is likely that Comet Tsuchinshan–ATLAS experienced orbital changes in the past, but as we shall see, its incoming orbit was near the uppermost limit of a possible stable orbit. If Comet Tsuchinshan–ATLAS has made multiple past perihelion passages, then its aphelion must have been shortened and then increased many times while avoiding catastrophic loss via ejection from the sun or a collision with a planet. That seems improbable on a 4.5-billion-year timescale.

It is likely that the orbit of Comet Tsuchinshan–ATLAS is very close to the maximum orbital size for comets bound to the sun.

The incoming semimajor axis of Comet Tsuchinshan–ATLAS was nearly 60% the distance to the nearest star (its aphelion distance was nearly 120% the distance to the nearest star). Obviously, the gravitational forces of other stars must affect the orbits of extremely long-period comets. How far from the sun can a comet orbit and still be gravitationally bound to the sun? Astronomers express the gravitational sphere of influence of a body as the Hill sphere. The Hill sphere of the sun has a radius of 230,000 AU (Chebotarev 1964). This distance is slightly less than the distance to the nearest star. More significantly, the Hill radius of the sun is slightly less than the semimajor axis of Comet Tsuchinshan–ATLAS. If one took the Hill radius as a definite limit of the sun’s gravitational influence, then one could question whether Comet Tsuchinshan–ATLAS is gravitationally bound to the sun at all. But the Hill radius is an approximation, not a hard and fast limit. It is likely that the orbit of Comet Tsuchinshan–ATLAS is very close to the maximum orbital size for comets bound to the sun.

How Old Can the Oort Cloud Be?

In a 4.5-billion-year-old solar system, how long has Comet Tsuchinshan–ATLAS followed its current orbit? As I pointed out earlier, during that time Comet Tsuchinshan–ATLAS would have made 40 perihelion passages. It is extremely unlikely that Comet Tsuchinshan–ATLAS could have survived that many orbits with no significant changes to its orbit. The usual answer is that Comet Tsuchinshan–ATLAS remained in the Oort cloud since the formation of the solar system 4.5 billion years ago, and only recently (57 million years ago) did a passing star’s gravity rob the comet of orbital energy and send it hurling toward perihelion this past October. Opposite to how gravitational perturbations near perihelion change aphelion distance, gravitational perturbations near aphelion change perihelion distances. But keep in mind that a passing star has about an equal probability of raising perihelion distances. This mechanism is believed to continually stir up objects in the Oort cloud, with some comets crashing toward the sun to put on quite a show as Comet Tsuchinshan–ATLAS did, with some comets liberated from the sun’s gravity altogether, but with most comets’ orbits merely rearranged within the Oort cloud.

How often do stars penetrate the Oort cloud to stir things up this way? Astronomers have come to realize that on a long timescale, it happens more often than once thought. A decade ago, a team of astronomers determined from proper motion and radial velocity that 70,000 years ago, a low-mass binary star passed within 50,000 AU of the sun (Mamajek et al. 2015). Dubbed Scholz’s star, this star was deemed too low in mass and moving too quickly to have stirred up the inner Oort cloud (< 20,000 AU) much but probably affected the outer Oort cloud at that time. That study used proper motion data from the Hipparcos mission, but a more recent study used the much more precise proper motion data from the Gaia mission for the star Gliese 710 (R. Fuente Marcos and C. Fuente Marcos 2020). They found that in 1.3 million years, Gliese 710 will pass as a little more than 10,000 AU from the sun. With considerably more mass than Scholz’s star, Gliese 710 (mass 57% of the sun) is expected to stir the Oort cloud tremendously, resulting in many bright comets every year for millions of years, as well as potentially civilization-ending impact events.

This raises the question of how often such events might occur. Also using the Gaia data, but with a dataset of 320,000 stars, another study found that a star capable of stirring up the Oort cloud passes the solar system about once every 50,000 years (Bailer-Jones 2015). Keep in mind that the author said that his study probably missed many other candidate interlopers. Thus, this estimate is probably conservative—the average time between encounters likely is shorter than this. If this estimate is reasonably correct and if the solar system were 4.5 billion years old, then throughout the solar system’s lifetime, there has been a staggering number of Oort cloud disturbances, nearly 100,000. However, the available data allow extrapolation over only a few million years. What is the probability that over a few billion years a massive, slow-moving star plunged deeply into the Oort cloud? We have no data to compute this, but that probability may be relatively high. This raises the question of whether the Oort cloud could have survived for billions of years. That would return us to the question of why we see comets in a very ancient solar system.

Conclusion

It may be that the long-term existence of the Oort cloud may be in doubt, jeopardizing its use as a rescuing device for the existence of comets.

For a long time, young-earth creationists have used the existence of comets today as evidence against a solar system that is 4.5 billion years old. The standard response to this problem for an ancient solar system is as comets cease to exist, they are continually replaced by new, incoming comets from the Oort cloud so that a quasi-steady state exists in the number of comets. The recent apparition of Comet Tsuchinshan–ATLAS pushes the limit of how far out the Oort cloud can extend. Furthermore, recent studies of stellar motion made possible by the highly precise Gaia data suggest that stellar interactions with the Oort cloud are far more common than previously thought. It may be that the long-term existence of the Oort cloud may be in doubt, jeopardizing its use as a rescuing device for the existence of comets. A Monte Carlo simulation of this problem by a creationary scientist would be most welcome.

References

Bailer-Jones, C. A. L. 2018. “The Completeness-Corrected Rate of Stellar Encounters with the Sun from the First Gaia Data Release.” Astronomy & Astrophysics 609 (January): A8.

Chebotarev, G. A. 1964. “Gravitational Spheres of the Major Planets, Moon and Sun.” Soviet Astronomy 7, no. 5 (March–April): 618–622. https://adsabs.harvard.edu/full/1964SvA.....7..618C.

Faulkner, Danny R. 1997. “Comets and the Age of the Solar System.” Journal of Creation 11, no. 3 (December): 264–273.https://answersingenesis.org/astronomy/comets/comets-and-the-age-of-the-solar-system/.

Fuente Marcos, Raul, and Carlos Fuente Marcos. 2020. “An Update on the Future Flyby of Gliese 710 to the Solar System Using Gaia EDR3: Slightly Closer and a Tad Later than Previous Estimates.” Research Notes of the American Astronomical Society 4, no. 12 (December): https://iopscience.iop.org/article/10.3847/2515-5172/abd18d#:~:text=Here%2C%20we%20present%20an%20updated,710%20to%20the%20solar%20system.

Giorgini, Jon D. n.d. “JPL/Horizons: Tsuchinshan–Atlas (C/2023 A3).” Last accessed January 10, 2025. https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%272023+A3%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%271800-01-01%27&STOP_TIME=%272200-01-01%27&STEP_SIZE=%27400%20years%27&CENTER=%27@0%27&OUT_UNITS=%27AU-D%27.

Blos, Art. 2022. “C/1980 E1 (Bowell).” Celestia. June 25. https://celestia.mobi/addon?item=E96E5A59-AEEF-8F44-66DD-DF45D12E3848.

Mamajek, Eric E., Scott A. Barenfeld, Valentin D. Ivanov, Alexei Y. Kniazev, Petri Väisänen, Yuri Beletsky, Henri M. J. Boffin. 2015. “The Closest Known Flyby of a Star to the Solar System.” Astrophysical Journal Letters 800, no. 1 (February): L17. https://ui.adsabs.harvard.edu/abs/2015ApJ...800L..17M/abstract.

Rao, Joe. 2024. “The Dazzling Comet Tsuchinshan-ATLAS Is Emerging in the Night Sky: How to See It.” Space.com. October 8. https://www.space.com/comet-tsuchinshan-atlas-bright-night-sky.

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