How an interstellar comet sheds light on universe's 'cosmic noon' Lisa Lock Scientific Editor Andrew Zinin Chief Editor Last year, an interstellar traveler entered our solar system. Some speculated that it was an alien spacecraft, but it turned out to be a comet, 3I/Atlas, and it provoked interest from astronomers and astrophysicists eager for insights into galaxies far, far away. Detailed observations from the National Aeronautics and Space Administration (NASA) shot down the alien spacecraft idea, but recent NASA analysis holds clues about the comet's ancient and, literally, alien origins.

With its powerful James Webb Space Telescope (JWST), NASA was able to capture detailed data on the interstellar traveler, including its chemical composition. The findings are akin to "alien chemistry" for an object that was likely formed 10 to 12 billion years ago in a still-mysterious period known as the universe's "cosmic noon," said Jacqueline McCleary, an assistant professor of physics at Northeastern University. "This clearly did not originate within our cosmic gene pool," McCleary said.

"This is sort of like gene sequencing a rose and then finding a fern. The building blocks are the same, but a lot has changed in the last few billion years to go from fern to rose." The most surprising discovery NASA made concerns 3I/Atlas' chemical composition. The comet has about 30 times the amount of deuterium, an isotope of hydrogen with double the mass of standard hydrogen, found in comets from our solar system, according to NASA.

This chemical makeup is indicative of an intensely cold system, McCleary said. While the presence of one isotope might not sound notable, it's enough to provide a glimpse of "a very different environment than our own solar system," McCleary said. For instance, the "heavy water" ice on the comet, composed of oxygen and deuterium instead of oxygen and hydrogen, points to a lack of long-term warmth in 3I/Atlas' home system that would typically reprocess all that material into the standard water found on Earth, she explained.

Combined with the trace amounts of carbon-13, a carbon isotope, detected in 3I/Atlas, it further marks the comet as an ancient interstellar object. As generations of stars form and die, they leave behind more and more heavy metals, like carbon-13, McCleary explained. The more of these metals a solar system has, the more recently it formed, she said.

"The fact that this comet seems to come from a system that's extremely metal-poor suggests that it has to have formed before many cycles of star formation and star death," she said. Our solar system formed around 4.5 billion years ago, relatively recent in terms of cosmic time. But NASA estimates that 3I/Atlas could have formed 10 to 12 billion years ago during a time in the universe's history known as "cosmic noon." This period, 2 to 3 billion years after the Big Bang, was the peak of star formation in the universe.

It's called cosmic noon because the sheer number of new, extremely hot stars made "the universe about as bright as it's going to get," McCleary said. This period of cosmic history has become less of a question mark in recent years, thanks to powerful tools like JWST.