NASA has released a collection of new observations capturing the flyby of 3I/ATLAS, a rare interstellar comet. First detected on July 1, it is only the third such object from outside our solar system ever observed passing through it. The data, gathered by a fleet of spacecraft, is already revealing unique clues about the visitor’s composition.
The US space agency released the new observations on Wednesday, which had been delayed by the recent government shutdown. As the comet passed Mars in October, multiple NASA missions were redirected to capture images of the fast-moving object, which reached speeds of up to 153,000 miles per hour (246,000 kilometers per hour).
Though none of the spacecraft were specifically designed to track comets, astronomers seized the rare opportunity. Nearly 20 mission teams collaborated on the effort, according to Nicky Fox, associate administrator for NASA’s Science Mission Directorate.
“It’s a little bit as if our NASA spacecraft were at a baseball game, watching the game from different places in the stadium,” said Tom Statler, lead scientist for solar system small bodies at NASA. “Everybody has got a camera and they’re trying to get a picture of the ball and nobody has a perfect view.”
Ahead of the Martian flyby, the Lucy and Psyche missions, along with solar-focused spacecraft like the Parker Solar Probe, SOHO, and PUNCH, all caught glimpses of the comet. Later, the Mars Reconnaissance Orbiter and Perseverance rover tracked it from the Red Planet. This provided an optimal viewing position, as Earth was on the opposite side of the sun at the time.
The European Space Agency’s ExoMars Trace Gas Orbiter, circling Mars since 2016, came about 10 times closer to the comet than telescopes on Earth. Its unique perspective allowed scientists to predict the comet’s future path with ten times greater accuracy. Other observatories, including the Hubble and James Webb space telescopes, have also studied the object.
Dr. Theodore Kareta, a planetary astronomer at Villanova University, noted the advantages of using multiple spacecraft. “Comets are three-dimensional objects, and looking at them from different angles will give us a much clearer picture of not just where they are and the trajectory they’re on, but also how large the nucleus of the comet is and the nature of any structures,” he said. Scientists are still refining measurements but believe the comet’s nucleus is between a few thousand feet and a couple of miles in diameter.
NASA officials also addressed public speculation that the object could be an alien spacecraft. “It looks and behaves like a comet, and all evidence points to it being a comet,” stated NASA Associate Administrator Amit Kshatriya. “But this one came from outside the solar system, which makes it fascinating, exciting and scientifically very important.”
Fox added that close monitoring has revealed no evidence of artificial origins, such as technosignatures. “But the super cool thing is not that it’s exactly like all the comets that we see in our solar system,” she said. “It’s the differences that are so tantalizing for us.”
Unlike comets from our solar system—often described as dirty snowballs of ice, rock, and dust—3I/ATLAS has a distinct composition. Scientists have noted it is releasing more carbon dioxide than water and more nickel than iron, differences that are still under investigation.
The comet made its closest approach to the sun on October 30. It is now reemerging into view for Earth-based telescopes and will swing within 168 million miles (270 million kilometers) of Earth on December 19 before continuing its journey out of our solar system.
Statler said the comet’s speed suggests it is ancient. “3I/ATLAS is not just a window into another solar system, it’s a window into the deep past—and so deep in the past that it predates even the formation of our Earth and our sun,” he said.
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