Scientists said that 3I/ATLAS, which was first seen in July, shone much faster than they expected, emphasising that they closely monitored the object, which entered the solar system from interstellar space and became the third in history.
Emphasising that comets usually form a tail of gas and dust as they approach the Sun, scientists point out that this is due to the Sun turning solid ice into vapour and removing material from their surfaces, which causes them to reflect more light.
According to scientists, observations made by NASA’s Solar-Earth Relations Observatory (STEREO), the European Space Agency’s Solar and Heliospheric Observatory (SOHO) and the National Oceanic and Atmospheric Administration’s GOES-19 weather satellite caught astronomers off-guard by the rapid increase in brightness of 3I/ATLAS.
“The reason for 3I’s rapid brightness increase, which far exceeds the brightness increase rate of most Oort cloud comets of similar [radial distance], is still unclear,” wrote Karl Battams, an astrophysicist at the Naval Research Laboratory, and Qicheng Zhang, a postdoctoral research associate at Lowell Observatory.
However, the two scientists offered several theories as to why 3I/ATLAS flares much faster than expected; “The first could be the object’s enormous speed. The object is travelling at about 137,000 mph, significantly faster than the two previously discovered interstellar objects.”
“Quirks in core properties such as composition, shape or structure – which could have been acquired from its host system or during its long interstellar journey – could likewise contribute to [the fast glow],” Zhan and Battams wrote.
The astronomers also emphasised that they discovered that 3I/ATLAS is “noticeably bluer than the Sun”, which is “consistent with gas emission contributing a significant fraction of the visible brightness near perihelion”.
“Without a physical explanation, the outlook for the post-perihelion behaviour of 3I remains unclear, and a plateau in brightness – or even a brief continuation of its pre-perihelion brightness – seems as likely as a rapid fading after passing perihelion,” the researchers added.
“After its perihelion on 29 October 2025, 3I will return to the twilight and then dark night sky in November-December 2025, after its perihelion on 29 October 2025,” Zhan and Battams wrote in the paper, adding that astronomers will have to be patient as 3I/ATLAS remains hidden from Earth behind the Sun. This may allow us to identify the comet in much more detail than is possible with the data presented,” they said.
