An ancient comet, 3I/Atlas, which journeyed through our solar system last year, is believed to have originated in a remarkably cold and isolated region of the galaxy, predating the formation of its own star system.
This celestial wanderer is only the third confirmed interstellar visitor and potentially the oldest, with scientists estimating its age at up to 11 billion years – more than twice that of our sun.
Researchers, led by the University of Michigan, used the ALMA observatory in Chile to study the comet last autumn. Their findings, published inNature Astronomy, reveal exceptionally high levels of deuterium, or heavy hydrogen, in the comet's water.
This suggests an origin in an environment significantly colder than our cosmic neighbourhood, existing even before its host star began to form, according to Teresa Paneque-Carreno of the University of Michigan. She noted that while our sun was likely surrounded by other nascent stars, this comet's parent star may have been more isolated, leading to less heating and persistently colder conditions.
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Discovered last summer, the comet offered NASA and the European Space Agency ample time to observe it with multiple space telescopes as it passed Mars in October and made its closest approach to Earth in December. It is now well beyond Jupiter, embarking on its permanent departure from our solar system, remaining visible only to professional astronomers.
The comet's precise place of origin is still unknown. Observations by theHubble Space Telescopeput the size of its nucleus somewhere between a quarter-mile and 3.5 miles (440 meters and 5.6 kilometers). It's hurtling 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 to stray into our celestial backyard —Oumuamua— was discovered by a telescope inHawaiiin 2017. Comet 2I/Borisov followed in 2019, named for the Crimean amateur astronomer who first spotted it.