Scientists have traced the origins of the latest interstellar comet to pass through our solar system, revealing that it likely came from a cold, isolated corner of the Milky Way that had yet to form its own solar system. The findings, published in Nature Astronomy, provide new insights into the early conditions of planet formation.
Comet 3I/Atlas: An Ancient Visitor
Comet 3I/Atlas, only the third confirmed interstellar visitor, is believed to be up to 11 billion years old—more than twice the age of our Sun. It was discovered last summer and observed by multiple space telescopes as it safely passed Mars in October and made its closest approach to Earth in December. Now beyond Jupiter, it is hurtling out of the solar system at 137,000 mph (220,000 kph).
Deuterium Clues to a Cold Origin
A team led by the University of Michigan used the ALMA observatory in Chile's Atacama Desert to study the comet last fall. They detected extremely high levels of deuterium, or heavy hydrogen, in its water. This suggests the comet formed in a region significantly colder than our cosmic neighborhood, before the Sun even existed. According to Teresa Paneque-Carreno of the University of Michigan, the comet's home star may have been a loner, resulting in less heating and colder conditions.
Size and Speed
Observations by the Hubble Space Telescope estimate the comet's nucleus is between a quarter-mile and 3.5 miles (440 meters to 5.6 kilometers) in diameter. It is now well past Jupiter and visible only to professional astronomers.
Implications for Planet Formation
Paneque-Carreno noted that linking these puzzle pieces together may provide insights into planet-forming conditions in the early universe. The first known interstellar object, Oumuamua, was discovered in 2017, followed by Comet 2I/Borisov in 2019.
