Non-periodic comets constitute some of the more unpredictable transient cosmic objects, both in terms of trajectory and in terms of peak brightness observed.
The more predictable periodic comets typically originate from the Kuiper belt, the region in the solar system just beyond Neptune, and have an orbital period of less than 200 years. Conversely, non-periodic comets typically originate from the farthest reaches of our solar system, from the scattered disk or from the Oort cloud, and can have orbital periods of thousands of years.
Comets are icy remnants orbiting the sun in highly elliptical orbits, left over from the formation of the solar system. As they approach the inner solar system in their orbit, they release gas and dust, giving rise to the typical dust and ion tails which comets are well known for.
On occasions, as they approach the inner solar system, comets can break up and disintegrate. This was one of the predicted probable outcomes for comet C/2023 A3 on its latest pass, as it reached perihelion – the closest point in its orbit to the sun – on September 27.
Discovered independently by two different observatories in early 2023, comet C/2023 A3 is one such non-periodic comet, with an estimated orbital period of some 80,000 years.
The comet was first spotted by the Purple Mountain Observatory in January 2023, and then confirmed by the Asteroid Terrestrial Impact Last Alert System (ATLAS) Observatory in February 2023. Initial predictive reports suggested that it might disintegrate and that its peak magnitude would remain around +3.0 at best – this was later revised, as the comet did not in fact disintegrate and as further observations were made.
Discovered independently by two different observatories in early 2023, comet C/2023 A3 is one such non-periodic comet, with an estimated orbital period of some 80,000 years
Indeed, the comet reached its peak observed brightness on October 9, reaching magnitude -4.9 and thus making it one of the brightest comets of the past century. Around this time, however, the comet was in conjunction with the sun and thus only visible in the morning sky, precluding ground observations.
The comet became visible in evening skies in the following few days, with observations recording a dimming of the comet after its closest approach to Earth on October 12, when it came as close as around 70 million kilometres to our planet. However, the comet remained visible to the naked eye for a number of days in the evening skies, as it now continues to recede back to the outer solar system.
Interestingly, a second comet was slated for its own perihelion passage around a month later.
Comet C/2024 S1 belonged to a group of comets termed Kreutz sungrazers. As the name suggests, these comets get extremely close to the sun’s surface in their orbit, sometimes just a few thousand kilometres away, and all originate from a singular cometary body that fragmented into several smaller bodies centuries ago.
Such comets have a very high risk of disintegrating completely upon reaching perihelion, with their close proximity to the sun causing their evaporation. When they survive such a passage, they can indeed become extremely bright, such as the Great Comet of 1965, which was actually visible in the daytime sky near the sun. Alas, C/2024 S1 did not survive its perihelion passage, indeed disintegrating completely on October 28.
Josef Borg completed a PhD in astronomy at the Institute of Space Sciences and Astronomy, University of Malta, and is currently a post-doctoral researcher in space bioscience at the Faculty of Health Sciences at the University of Malta.
Sound Bites
• Voyager 1 used a back-up radio transmitter for the first time since 1981. Currently, the farthest man-made object from Earth, Voyager 1 is at a distance of almost 23 light hours from Earth – over 24 billion kilometres away. Recent communication issues had been due to the spacecraft’s autonomous fault-protection system, which turned off the main X-band radio transmitter – reason for this is currently still unknown.
The spacecraft, however, switched to its back-up S-band antenna, not used since 1981, which draws less power but also broadcasts a much fainter signal. Notwithstanding this, the Voyager 1 team still managed to reconnect with the spacecraft and is working on finding an answer as to why the fault protection system was triggered.
For more soundbites, listen to Radio Mocha every Saturday at 7.30pm on Radju Malta and the following Monday at 9pm on Radju Malta 2 https://www.fb.com/RadioMochaMalta/.
DID YOU KNOW?
• Comet Levy/-Shoemaker 9 was observed to collide with Jupiter in July 1994. The comet is thought to have been captured in a Jovian orbit by the giant planet some time in the 1970s. After fragmenting in July 1992, the comet fragments were discovered in 1993 and then collided with Jupiter’s southern hemisphere at an estimated velocity of 60km/s (or 216,000km/h) between July 16 and July 22, 1994.
• Comets crossing the Earth’s orbital plane give rise to most periodic meteor showers. As a comet recedes to the outer solar system, it leaves debris lingering behind in its wake. As it travels around the sun, the Earth periodically crosses these debris trails, with such particles entering the Earth’s atmosphere and burning upon entry, causing the ‘shooting star’ appearance of the meteors. Nearly all major periodic meteor showers result from such comets, barring the Geminid meteor shower which originates from an asteroid – 3200 Phaethon.
For more trivia, see: www.um.edu.mt/think.