Recent observations of comet 3I/ATLAS during last week's total lunar eclipse have revealed a stunning transformation: the interstellar visitor may be turning a bright green as it approaches the halfway point on its journey through the solar system. If confirmed, this unexpected change is attributed to the comet's increasing proximity to the sun, according to experts.
Discovered in early July, 3I/ATLAS is a roughly 7-mile-wide (11 kilometers) comet traveling towards Earth at an astonishing speed of over 130,000 mph (210,000 km/h). This comet originates from beyond the orbit of Jupiter and was identified as an interstellar object, indicating that it is on a one-way trip through our solar system. It is believed to have been ejected from a distant star system within the Milky Way, making it significantly older than our solar system.
As the comet approaches its closest flyby of Mars next month, it is also set to reach its minimum distance from the sun on October 29. The closer it gets to the sun, the more solar radiation it absorbs, leading to an increase in the expulsion of ice, gas, and dust from its core. This process has allowed 3I/ATLAS to develop a traditional cometary tail.
On September 7, astrophotographers Michael Jäger and Gerald Rhemann captured remarkable images of 3I/ATLAS against the dark skies of Namibia during the total lunar eclipse, also known as the blood moon. This celestial event provided darker-than-usual skies, enhancing visibility of the comet. The resulting photographs showcase the comet's surprising emerald hue, suggesting that its proximity to the sun is causing changes in its composition as new, rarer chemicals are expelled from its core, as reported by Spaceweather.com.
However, it is important to note that it is still early to determine if this change is indeed permanent, as no other photographers or observatories have yet confirmed this green coloration.
This is not the first instance of astronomers observing a green glow emanating from a comet. In recent years, several comets have exhibited similar emerald hues. Notable examples include the aptly named green comet C/2022 E3, which made its appearance in early 2023, and the explosive devil comet 12P/Pons-Brooks that also turned green as it approached the sun in 2024. Earlier this year, astronomers also discovered another green comet known as SWAN25F.
The primary cause of this rare green coloration in comets is typically attributed to the presence of dicarbon in the ice and gas clouds surrounding them, known as their comas. Dicarbon, also referred to as diatomic carbon, is a molecule consisting of two bonded carbon atoms. In its pure form, carbon usually exists as solitary atoms or within larger structures, like diamonds.
While spectroscopic observations of 3I/ATLAS have yet to detect dicarbon in its coma, scientists speculate that this molecule may be hidden beneath layers of ice that have melted due to solar radiation. Alternatively, the comet's green glow could result from a different mix of gases or dust, creating a classic cometary appearance with unfamiliar chemistry.
Avi Loeb, an astronomer from Harvard University known for his research into interstellar objects, proposes another explanation for the comet's color. He suggests that the presence of cyanide, which was detected in the comet's coma by the Very Large Telescope in Chile's Atacama Desert, may be responsible for the observed hue. As a result, further observations and photographic evidence will be crucial in the coming weeks to validate this new coloration and discern its origins.
Unfortunately, as 3I/ATLAS continues its journey, it will soon be out of view as it passes the sun on the opposite side from Earth. However, it is expected to reappear in a few months, just before reaching its closest point to Earth in December. At that time, it will be approximately 700 times further away from us than the moon.
As astronomers continue to study this remarkable interstellar visitor, the intrigue surrounding comet 3I/ATLAS only deepens, promising more exciting discoveries in the near future.
