C/2023 A3 and the role of comets in space

Comets are among the most intriguing objects in our solar system. These icy bodies, originating from distant and dark regions of space, such as the Kuiper Belt and the Oort Cloud, are ancient relics of the early solar system's formation. 

Frozen messengers

Often described as “cosmic time capsules,” comets preserve the primordial material from which the Sun and planets formed. Their study provides critical insights into the origins and evolution of our cosmic neighbourhood. From historical comets like Halley's Comet to modern-day discoveries such as Comet C/2023 A3, these celestial travellers continue to fascinate scientists and the general public.

Origin and composition of comets

Comets are primarily composed of volatile ices – such as water, carbon dioxide, methane, and ammonia—mixed with rocky and organic materials. The characteristic dust tail forms as the comet approaches the Sun, sublimating and releasing dust particles that are carried away and dispersed along its orbit.

Unlike the ion tail, which is strongly affected by solar wind pressure, the dust tail is only minimally influenced. The tail always points in the opposite direction of the Sun due to radiation and solar wind. The nucleus of a comet remains its core, usually a few kilometres wide, while the coma can expand up to 100,000 kilometres or more as the comet heats up.

Structure of the Comet Hale–Bopp. / © Rolando Ligustri

Originating from two primary regions – the Kuiper Belt and the Oort Cloud – comets offer a glimpse into two distinct eras of Solar System formation. The Kuiper Belt lies just beyond Neptune’s orbit, home to short-period comets like Halley's Comet, which return regularly.

The Oort Cloud, a distant and spherical region far beyond Pluto, harbours long-period comets, which may take hundreds of thousands of years to return, such as Comet Hale-Bopp.

The role of comets in solar system science

For decades, comets have played a pivotal role in helping scientists understand the early conditions of the Solar System. By studying the isotopic composition of water and gases in comets, scientists attempt to unravel the mysteries of Earth's own water origin. Comets are also considered key candidates for delivering organic molecules to the early Earth, potentially seeding the precursors of life.

Comet 67P. / © Rolando Ligustri

The Rosetta mission, which successfully orbited Comet 67P/Churyumov-Gerasimenko in 2014, provided some of the most detailed data on a comet ever collected. Findings included the discovery of molecular oxygen and the detection of amino acids, further supporting the idea that comets could have played a role in the origins of life.

According to Altwegg et al. (2019), “the isotopic signature of water from comet 67P is distinctly different from Earth’s oceans”, indicating the complex role comets may have had in Earth’s water source.

C/2023 A3: The comet of the moment

Currently captivating the scientific community, Comet C/2023 A3 (Tsuchinshan-ATLAS) has garnered significant attention as it travels across the inner solar system. Discovered in early 2023 by the ATLAS survey and the Tsuchinshan Observatory, C/2023 A3 is a long-period comet from the Oort Cloud. Early observations suggest that it may become one of the brightest comets of the decade, potentially visible to the naked eye.

Preliminary estimates suggest that C/2023 A3 could reach a magnitude of between 0 and -5 at its peak, depending on its activity level and proximity to Earth at the time of observation. As reported in The Astronomical Journal, Meech et al. (2023) describe C/2023 A3 as “an exceptionally active comet with high levels of water and carbon monoxide outgassing”, making it a promising candidate for both visual observation and scientific study.

Early spectroscopy data has already revealed a high concentration of volatile ices, particularly water and carbon monoxide, which are driving its early activity. The comet's dust tail, formed by solar radiation pressure, is growing, and ground-based observatories are closely monitoring its progression. According to data from the Minor Planet Center (MPC) and International Astronomical Union (IAU), C/2023 A3 is likely to provide an exceptional observational event, not just for amateur astronomers, but for planetary scientists as well.

Comet C/2023 A3. / © www.virtualtelescope.eu

The excitement surrounding C/2023 A3 isn’t just about its potential for spectacular visibility. Scientific missions have already been proposed to study the comet. As researchers use ground-based observatories and space-based platforms to analyse its composition and behaviour, C/2023 A3 presents an unprecedented opportunity to learn more about Oort Cloud comets – an enigmatic class of objects that rarely make such close approaches to the Sun.

Studies of comets like C/2023 A3 also allow astronomers to refine models of Solar System formation. The analysis of isotopic ratios in these comets' ices can reveal the conditions in the solar nebula from which the Solar System emerged. As Bockelée-Morvan et al. (2004) noted in their research, “Cometary volatiles are particularly interesting because they are likely to have been preserved in a pristine state from the epoch of planet formation”.

Key dates for observation

Closest approach to Earth: 9 October 2024

During this period, the comet passed relatively close to Earth, further enhancing its visibility. This proximity could have lead to the comet being visible with small telescopes, binoculars, or even the naked eye, depending on local conditions.

Optimal observation window: late September to early November 2024

The best time to observe C/2023 A3 will likely be in the weeks from late September to early November 2024. During this time, the comet is expected to be high enough in the sky and bright enough to be a prominent feature, particularly in darker, low-light pollution areas.

Observation tips

Use binoculars or a telescope early on: Although the comet might become visible to the naked eye around perihelion, binoculars, or a small telescope will offer better views, especially before its brightest phase.

Dark skies are essential: Observing the comet from a location with minimal light pollution will greatly enhance your viewing experience. The darker the skies, the more prominent the comet’s tail and coma will appear.

Be prepared for variability: Comet brightness is notoriously unpredictable. While C/2023 A3 is expected to be bright, comets sometimes underperform due to outgassing or disintegration. Keeping an eye on astronomical reports close to the perihelion will give you the most accurate information on its visibility.

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A special thanks to my friend Rolando Ligustri who provided some of the incredible come photos used in this article. Rolando is a renowned Italian comet researcher and master imager, with over three decades of experience in astrophotography. Known for his unique contributions to comet studies, Rolando's stunning images have been featured in numerous international publications, and his work continues to inspire the global astronomy community.

Adriano Anfuso is a photographer and digital creator who is passionate about capturing the awe-inspiring beauty of the cosmos and Earth's wonders. You can check out his work here.