Comet 3I/ATLAS: A 12-Billion-Year-Old Interstellar Visitor
Scientists studying the interstellar comet 3I/ATLAS have determined that it formed an estimated 10 to 12 billion years ago in a primordial planetary system, making it the oldest known object to venture through the solar system. The comet, with a diameter of about 1.6 miles (2.6 km), has a composition unlike anything found in our solar system, according to a study published in the journal Nature.
Unique Chemical Makeup Revealed by James Webb Space Telescope
The researchers, led by Martin Cordiner, a planetary scientist and astrochemist at NASA's Goddard Space Flight Center, used the James Webb Space Telescope to measure isotope ratios of hydrogen and carbon on 3I/ATLAS. The comet's water contains about 30 times more deuterium—a hydrogen isotope—than other comets in the solar system. Its carbon isotope ratios also differ from those seen in solar system objects and nearby interstellar clouds.
Born in a Cold, Primordial Environment
The study indicates that 3I/ATLAS formed in a much colder environment—roughly minus-405 degrees Fahrenheit (minus-243 degrees Celsius)—than the one in which Earth and other solar system bodies formed about 4.5 billion years ago. According to Cordiner, the comet's host system was likely colder and less metal-rich, but more heavily irradiated by ultraviolet light and cosmic rays.
Rich in Organic Molecules Despite Cold Origin
Despite its cold and distant origins, 3I/ATLAS is rich in organic molecules containing carbon, hydrogen, nitrogen, oxygen, and sulfur. Cordiner noted that this shows the volatile elements for life were abundant in its distant planet-forming disk. The carbon composition suggests the comet formed during a period of intense star formation in its region, when the universe was only about 13% of its current age (the Big Bang occurred about 13.8 billion years ago).
Potential Origin in the Milky Way or Nearby Galaxies
The researchers believe 3I/ATLAS likely formed in the Milky Way, but based on its age, they cannot rule out an origin in another galaxy. Cordiner explained that it could take as little as a billion years for a fast interstellar object to travel from the Magellanic Clouds, the nearest galactic neighbors. The comet may have been expelled from its home planetary system due to gravitational interactions with planets or a collision.
Comparison to Previous Interstellar Objects
3I/ATLAS is only the third interstellar object observed in the solar system, following 1I/'Oumuamua in 2017 and 2I/Borisov in 2019. The researchers are confident it is a natural object, despite past speculation that it might be an alien spacecraft. Cordiner stated that the evidence was clear from an early stage that it was a comet-like object, and subsequent observations have confirmed that interpretation.
Current Trajectory and Future Exit
3I/ATLAS is now approaching the orbit of Saturn and is expected to pass beyond Pluto's orbit in 2029, exiting the solar system's outer boundary around 2035. Its journey through the solar system provides a unique opportunity to study the chemical and physical conditions of a distant planetary system formed billions of years ago.
