A comet that passed through our solar system from another star last year likely originated in a cold, isolated corner of the galaxy that had not yet formed its own solar system, astronomers reported on Thursday.
Ancient Interstellar Visitor
Comet 3I/Atlas is only the third confirmed interstellar visitor and may be the oldest. Scientists estimate it could be up to 11 billion years old, more than twice the age of the Sun.
A team led by the University of Michigan used the ALMA observatory in Chile's Atacama Desert to study the comet last fall. The harmless iceball was discovered last summer, giving NASA and the European Space Agency time to aim multiple space telescopes at it as it passed Mars in October and made its closest approach to Earth in December. It is now beyond Jupiter, leaving our solar system permanently, still visible only to professional astronomers.
High Deuterium Levels
In the study, scientists detected extremely high amounts of deuterium, or heavy hydrogen, in the comet's water. This suggests the comet formed in a place much colder than our cosmic neighborhood, before the Sun even existed. University of Michigan's Teresa Paneque-Carreno noted that while our Sun may have been surrounded by other newborn stars during formation, this comet's home star might have been more isolated, leading to less heating and colder conditions.
The findings were published in Nature Astronomy.
Unknown Origin
The comet's precise place of origin remains unknown. Observations by the Hubble Space Telescope suggest its nucleus is between 0.25 miles and 3.5 miles (440 meters to 5.6 kilometers) across. It is moving away at 137,000 mph (220,000 kph).
Linking all these "puzzle pieces together may give an idea to how the planet-forming conditions were at these early times," Paneque-Carreno said in an email.
The first known interstellar object, Oumuamua, was discovered in Hawaii in 2017. Comet 2I/Borisov followed in 2019, named after the Crimean amateur astronomer who first spotted it.
