Recently, reports circulated of the interstellar comet 3I/ATLAS changing colours during its solar approach, adding to its mysterious nature. A lack of explanation fuelled suspicions of the visitor being alien technology, as suggested by physicist Avi Loeb, but now we have a rebuttal for at least one of the many claims.
Discovered on July 1 by the NASA-funded Asteroid Terrestrial-impact Last Alert System (ATLAS), this comet is the third confirmed interstellar object to visit our solar system. It reached perihelion (closest point to the Sun) on October 30 and underwent sudden increase in brightness, puzzling scientists.
Qicheng Zhang, a postdoctoral fellow at the Lowell Observatory in Arizona, wrote in a pre-print study that the comet appeared “distinctly bluer than the Sun” but contrary to reports, there’s no evidence that the comet changed colours multiple times. That being said, its increased illumination is still a mystery.
The latest observations, made by various space-based telescopes like the Solar and Heliospheric Observatory (SOHO), the weather satellite GOES-19, and the twin-Solar Terrestrial Relations Observatory (STEREO), show that the comet has a blue/green cloud of gas and dust (coma) and it’s still the same colour, only brighter.
“As far as we know, the comet just ‘changed color’ once when its gas coma first became visible/bright, and it’s still like that now,” Zhang told Space.com.
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The brightness aspect was also flagged by Loeb, who has listed ten anomalies of 3I/ATLAS. Another highly discussed aspect of its transit is a lack of cometary tail which should have been visible post perihelion. Several pictures taken after October 30 show the comet as a fuzzy bright dot, which is unusual because as a comet passes the Sun, its heat causes the surface ice deposits to sublimate (turn directly into gas). This gas, mixed with dust, forms a tail that can extend millions of kilometres into space.
Loeb says that if 3I/ATLAS is a natural comet, it must have lost about 13% of its mass (33 billion tons) at perihelion, but a lack of tail is very unusual. One of the explanations for it is that high concentration of carbon dioxide on the comet’s 5 km wide nucleus is causing ‘evaporative cooling,’ and is not allowing the low amount of water-ice to sublimate and get released. [Tap here to read more about it]. In contrast, native comet Lemmon started showing an enormously long tail days before reaching perihelion on November 8.
3I/ATLAS is currently behind the Sun from our perspective and will reportedly make closest approach to Earth on December 19 at around 270 million kilometres. Scientists hope they will get a better view of the comet which may help in uncovering its many mysteries.
ALSO READ: Comet 3I/ATLAS Vs Comet Lemmon: Why The Former Has No Tail Post Perihelion
