3I/ATLAS may have just changed color — for the third time
Recent observations of the interstellar object 3I/ATLAS show that it has developed a faint blueish hue, hinting at a potential color change. This is the third time experts have seen the comet’s coloring shift since it was discovered
This is the third time that experts have noted a potential change to the comet’s color — but, so far, none of them have stuck.
3I/ATLAS, the third-known interstellar object to visit our solar system, was spotted shooting toward the sun at more than 130,000 mph (210,000 km/h) in early July.
The comet is potentially the oldest of its kind ever seen and was likely ejected from its home star system, somewhere in the Milky Way’s frontier, more than seven billion years ago.
Since then, it has sailed through interstellar space, before making its current rendezvous with our solar system.
The comet reached its closest point to the sun, known as perihelion, on Oct. 29, when it was mostly hidden from us, reaching a minimum distance of 130 million miles (210 million kilometers) from our home star — around 1.4 times farther from the sun than Earth.
The day before, a pair of researchers analyzing data from spacecraft that could still see 3I/ATLAS revealed that the comet had brightened by several orders of magnitude after disappearing from view, which can’t be fully explained by its proximity to the sun.
In the same paper, the researchers also wrote that the comet appears to be “distinctly bluer than the sun,” which came as a surprise given that this color had not been seen in the comet until now.
This color change is likely the result of a specific gas, such as carbon monoxide or ammonia, leaking from the comet, they argued. (This study has not yet been peer-reviewed, and no other observations have thus far confirmed the blue coloration.)
The researchers noted that the blue coloration is in sharp contrast to the initial red hue given off by the comet during early observations in July, which was likely the result of an abundance of dust coming off its surface.
Then, in September, the comet briefly appeared to be turning green, likely due to the presence of dicarbon or cyanide within its coma.
But these changes of coloration were only temporary, and it’s currently unclear why that is.
Only time and continued observations will tell if the comet’s new coloring will stick.
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Header image: NASA / ESA