Comet 3I/ATLAS Approaches the Sun, Offering Unique Insights

A rare celestial event is set to unfold as comet 3I/ATLAS approaches its perihelion on October 30, 2023. During this closest point to the Sun, located approximately 1.35 astronomical units (about 125 million miles or 202 million kilometers) away, the comet is expected to exhibit heightened activity. However, observers on Earth will be unable to witness this spectacle, as the comet is currently obscured by the Sun’s intense glare.

The phenomenon occurs when solar warmth causes the ice on the comet’s surface to sublimate, transforming into gas. This process creates a glowing cloud known as a coma around the nucleus and often generates two distinct tails: one composed of dust and the other an ion tail made of charged particles propelled by solar winds. As 3I/ATLAS reaches perihelion, this outgassing is anticipated to peak, significantly increasing its brightness.

Unfortunately, the view from Earth is compromised. Since late September, 3I/ATLAS has been in solar conjunction, making it invisible to terrestrial telescopes, including the renowned Hubble and James Webb space telescopes. They will only have the opportunity to observe the comet again in late November or early December.

Robotic Explorers Positioned to Observe

While Earth-based observers are left in the dark, a fleet of robotic spacecraft across the solar system is well-positioned to observe the comet’s approach. Notably, missions orbiting Mars had a clear view of the comet when it passed just 0.19 astronomical units (approximately 17.6 million miles or 28.4 million kilometers) from the Red Planet on October 3, 2023. These missions will continue to monitor 3I/ATLAS as it rounds the Sun.

Other missions, including NASA’s Psyche, which is en route to an asteroid of the same name, and the Lucy mission, heading toward Jupiter’s Trojan asteroids, are also set to observe the perihelion. The European Space Agency’s JUICE probe, which recently conducted a fly-by of Venus, is also aligned in the comet’s direction. However, it is currently using its primary antenna as a sun shield, delaying data transmission until February 2024.

Scientific Insights from a Distant Visitor

The scientific community is particularly interested in the chemical composition of 3I/ATLAS. The gas and dust released during the outgassing process provide direct samples of the comet’s makeup, offering valuable insights into the star system where it formed over seven billion years ago.

Preliminary findings indicate that 3I/ATLAS has a higher concentration of carbon dioxide and nickel compared to comets originating from our solar system. These distinctions enable astronomers to draw comparisons between the chemical profiles of our solar system and that of the comet’s distant origins. Researchers are keenly observing for any new molecules that may emerge during the peak activity at perihelion, particularly iron emissions, which have yet to be detected.

As 3I/ATLAS re-emerges from behind the Sun in late November, it may still exhibit significant activity. Although anticipated to be faint, with a predicted magnitude of 12, it could be within reach for astro-imagers and those using advanced telescopes. The powerful optics of the Hubble and James Webb space telescopes will make it an accessible target for detailed observation.

The approach of 3I/ATLAS not only captivates astronomers but also highlights the capabilities of modern space missions to capture events that remain hidden from our planet. As the comet makes its closest passage through the solar system, it provides a unique opportunity to study the building blocks of our universe and the processes that govern celestial bodies.