Comet 3I/ATLAS, the third known interstellar visitor, is exhibiting unexpected brightness as it approaches perihelion, its closest point to the Sun. Recent observations indicate that the comet has been brightening at a significantly accelerated pace. Ground-based observations have been challenging due to the comet”s position behind the Sun for the past month, prompting astronomers to rely on space-based observatories for data.
A notable development in this observation effort involves the use of solar-monitoring satellites. Researchers Qicheng Zhang from Lowell Observatory and Karl Battams from the US Naval Research Laboratory discovered that spacecraft designed to monitor the Sun”s corona could also observe the comet. Utilizing instruments aboard STEREO-A, SOHO, and GOES-19, they documented the comet”s remarkable transformation.
Between mid-September and late October, as 3I/ATLAS moved from approximately 2 astronomical units (AU) to about 1.36 AU from the Sun, its brightness surged. The research team calculated that the brightness increased in proportion to the inverse of the heliocentric distance raised to the 7.5 power, indicating a much steeper brightening rate than previously observed when the comet was farther away. This contrasts with the typical gradual brightening seen in most comets as they approach the Sun and their icy components sublimate into gas.
Additionally, the comet has been observed to glow distinctly blue, suggesting a significant contribution of gases to its visible brightness rather than just dust. Previous observations had noted a reddish hue in its dust, making this blue shift particularly intriguing. The researchers speculate that emissions from molecules like cyanogen and possibly ammonia could be responsible for this unexpected coloration.
Images captured by the coronagraph on GOES-19 showed the comet as an extended object, featuring a visible atmosphere or coma approximately four arc-minutes wide. This glowing envelope of gas and dust around the nucleus confirms that 3I/ATLAS is actively shedding material as it experiences increased solar heating.
On October 29, the comet reached perihelion, with calculations indicating it may have brightened to around magnitude 9, a level detectable by smaller amateur telescopes. As it moves away from the Sun and returns to darker skies in November and December, ground-based observers will finally have the opportunity to analyze this extraordinary interstellar object in greater detail.
The cause of this rapid brightening remains uncertain, with researchers considering factors such as the comet”s unique composition, its swift approach, or potential peculiarities from its extensive journey through interstellar space. A preprint of their research findings is available on arXiv.
This report was initially published by Universe Today.
