Ancient Comet 3I/ATLAS Passes Earth, Revealing Galactic Secrets

In the early hours of December 19, 2025, Comet 3I/ATLAS made its closest approach to Earth, passing at a distance of 168 million miles (approximately 1.8 astronomical units). Discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Chile on July 1, 2025, this ancient comet represents a unique opportunity for astronomers to study a cosmic relic that predates our solar system.

The comet, travelling at a remarkable speed of 42 miles per second (68 km/s), follows a hyperbolic orbit with an eccentricity of 6.13. This is the highest recorded for any visitor to the solar system, indicating that 3I/ATLAS is not bound to the Sun’s gravitational pull and will eventually exit our solar system. Its journey began in the ‘thick disk’ of the Milky Way, a region rich in some of the galaxy’s oldest stars, entering our vicinity from the direction of the Sagittarius constellation.

According to Matthew Hopkins, an astronomer at the University of Oxford, the comet is estimated to be over 7.6 billion years old, with some models suggesting it could be as ancient as 11 billion years. This makes 3I/ATLAS possibly the oldest physical object ever detected by humanity, a true time capsule from a different era of galactic history. Its nucleus is estimated to measure between 0.3 and 5.6 kilometres in diameter.

Recent observations from the Gemini North telescope in Hawaii revealed a ghostly green glow emanating from the comet, a classic indicator of ‘outgassing’. This phenomenon occurs as gases evaporate, reflecting sunlight as the Sun warms the icy core of the comet. Data from the James Webb Space Telescope (JWST) and the European Space Agency’s Mars Trace Gas Orbiter confirmed that 3I/ATLAS is accelerating as it moves away from the Sun. This acceleration is due to jets of vaporised gas escaping the surface, a common behaviour among comets, rather than any artificial propulsion.

Chemical analyses conducted by JWST showed that 3I/ATLAS is notably rich in carbon dioxide, containing traces of methanol nearly four times greater than the concentration found in local comets. Additionally, it includes nickel and cyanide gas, suggesting that while this interstellar visitor hails from another star system, it is composed of the same fundamental materials—ice, rock, and dust—found in our own solar neighbourhood.

As Comet 3I/ATLAS begins its long exit from our solar system, the opportunity for observation is rapidly diminishing. The Virtual Telescope Project in Italy is scheduled to host a live YouTube webcast at 23:00 EST, offering a final chance for viewers to witness this extraordinary object as it heads towards the constellation Gemini.

While excitement surrounding the comet has led to speculation about alien technologies, the scientific evidence strongly supports its natural origin. As humanity prepares for a new era of discovery with the upcoming Vera C. Rubin Observatory, Comet 3I/ATLAS serves as a haunting reminder of our place in a vast and ancient galaxy. It is a fleeting glimpse into a deep past, here today and destined to vanish into the cosmic dark forever.