The interstellar invader Comet 3I/ATLAS is continuing to surprise scientists, this time by brightening at an unexpectedly rapid pace as it made its closest approach to the sun.
The brief presence of these bodies in the solar system offers a unique glimpse into the chemical makeup around other stars.
Scientists had expected 3I/ATLAS to brighten as it made its closest approach to the sun, or reached perihelion, on Wednesday (Oct. 29).
The team proposes a few different mechanisms that could account for the unexpectedly rapid brightening of this comet from beyond the solar system.
It could be the result of the speed at which 3I/ATLAS is approaching the sun; alternatively, it could tell scientists something about the comet itself.
Scientists are still in awe of the interstellar invader Comet 3I/ATLAS, which this time brightened at a startlingly quick rate as it approached the sun. The reason why that occurred is still unknown to experts studying the object.
After the cigar-shaped space-rock “Oumuamua,” which was found to be traveling through the solar system in October, 3I/ATLAS is only the third object known to have entered our solar system from another planetary system. 2017, and in August 2019, the first interstellar comet, 2I/Borisov, was observed in our stellar backyard. A unique window into the chemical composition surrounding other stars is provided by these bodies’ brief existence in the solar system.
When 3I/ATLAS reached perihelion, or its closest approach to the sun, on Wednesday (October), scientists had anticipated that it would brighten. (29. This is a common occurrence for comets that originate from the Oort Cloud, a shell of icy bodies at the solar system’s edge. It occurs as a result of a process known as sublimation, which is the direct transformation of solid ice into gas by solar radiation. The comet’s halo, coma, and distinctive cometary tail all grow as a result of this gas’s subsequent eruption from the comet’s shell. The dust increases the comet’s brightness by reflecting light. On the other hand, 3I/ATLAS brightened considerably faster than expected.
The researchers, Karl Battams, an astrophysicist at the Naval Research Laboratory (NRL) in Washington, DC, and Qicheng Zhang of Lowell Observatory in Flagstaff, Arizona, write in a paper discussing the observation posted on the research repository site arXiv, “The reason for 3I’s rapid brightening, which far exceeds the brightening rate of most Oort cloud comets at similar r [radial distance], remains unclear.”.
The sun-observing Solar and Heliospheric Observatory (SOHO), the weather satellite GOES-19, and STEREO-A and STEREO-B, the twin spacecraft that comprise Solar Terrestrial Relations Observatory (STEREO), all noticed the sudden brightening of 3I/ATLAS. Because ground-based instruments won’t be able to observe the interstellar comet again until it passes out from the other side of the sun into its “postperihelion” phase and escapes the glare of starlight in mid-to late-November 2025, space-based observations were required.
The group suggests several explanations for the comet’s surprisingly quick brightening from outside the solar system. It might be caused by the speed at which 3I/ATLAS is getting closer to the sun, or it might provide information about the comet itself. This is intriguing because it may indicate that the planetary system from which 3I/ATLAS originates has a different chemical makeup if its internal composition differs from that of the nuclei of Oort cloud comets.
“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],” Zhan and Battams went on. The outlook for 3I’s postperihelion behavior is still unclear in the absence of a proven physical explanation, and a brightness plateau or even a brief continuation of its preperihelion brightening seems as likely as rapid fading past perihelion. The “.
Additionally, because the interstellar comet was still dominated by carbon dioxide sublimation at an unusually close distance from the sun—roughly three times the distance between Earth and our star—the authors speculate that sublimation may be taking place differently than anticipated for 3I/ATLAS. This might have caused cooling, which had previously prevented water ice from sublimating into steam.
It’s obvious that 3I/ATLAS still confounds and fascinates scientists in equal measure, and it’s safe to assume that once it escapes the sun’s glare, we’ll find even more mysteries about this interstellar intruder.
The two scientists came to the conclusion, “Continued observations may help provide a more definitive explanation for the comet’s behavior.”.
