Astronomers are investigating why interstellar comet 3I/ATLAS brightened much faster than expected near the Sun, suggesting its composition or speed may hold the answer.
Astronomers are intrigued by 3I/ATLAS, an interstellar object that has brightened far faster than expected as it raced through the solar system, reaching its closest point to the Sun on October 29.
First detected in early July, 3I/ATLAS is only the third known visitor from interstellar space, and scientists suspect it is a comet. Its rapid increase in brightness during its solar approach has defied expectations, with researchers observing the phenomenon through NASA’s Solar Terrestrial Relations Observatory (STEREO), the European Space Agency’s Solar and Heliospheric Observatory (SOHO), and NOAA’s GOES-19 satellite.
“The reason for 3I’s rapid brightening, which far exceeds the brightening rate of most Oort cloud comets at similar [radial distance], remains unclear,” Naval Research Laboratory astrophysicist Karl Battams and Lowell Observatory postdoctoral fellow Qicheng Zhang wrote in a recent paper.
They suggested several possibilities, including its extraordinary speed of about 137,000 miles per hour—much faster than previous interstellar objects—or unusual composition. “Oddities in nucleus properties like composition, shape, or structure — which might have been acquired from its host system or over its long interstellar journey — may likewise contribute [to the rapid brightening],” they noted.
The researchers also observed that 3I/ATLAS appears “distinctly bluer than the Sun,” suggesting gas emissions play a major role in its brightness. However, its behavior after perihelion remains uncertain.
“Without an established physical explanation, the outlook for 3I’s postperihelion behavior remains uncertain,” they wrote, adding that new observations in December may finally reveal more about the mysterious traveler.