Recent observations of interstellar comet 3I/ATLAS have revealed a fascinating display: the comet is radiating a distinct green glow and surprisingly, appears to be concealing its tail. However, experts assure that this does not indicate any problems with the comet; rather, it provides valuable insights into its composition and behavior as it journeys through our solar system.
A Closer Look with the Lowell Discovery Telescope
Researcher Qicheng Zhang, working at the Lowell Observatory in Arizona, utilized the powerful Discovery Telescope to capture fresh images of the comet on Wednesday, November 5. The observations were made as the comet moved away from the sun after completing a swing around its far side.
Why the Green Glow? Understanding Diatomic Carbon
Like most comets nearing the sun, 3I/ATLAS develops a cloud of gas and dust known as a coma as ice and other materials sublimate (transition directly from solid to gas) due to solar heating. Zhang’s observations focused on diatomic carbon (C2) particles, which produce a distinctive green glow when viewed through a specific filter.
He explained that the comet contains large hydrocarbon molecules – those comprised of carbon and hydrogen. When exposed to ultraviolet (UV) light from the sun, these molecules break apart. “It’s sort of like why we get sunburned if we stay out in the sun too long without sunscreen,” Zhang explained. The UV light destroys cells in our skin; similarly, it breaks down the molecules in the comet. A byproduct of this process is diatomic carbon, which is easily detected by astronomers.
The Tail’s Appearance: An Unusual Perspective
While the images suggest a lack of a dust tail, astronomers aren’t concerned. Close examination reveals a slight brightness on the left side of the comet, indicative of its tail. Zhang explained that this asymmetry arises because the tail is seen head-on and positioned directly behind the comet, curving slightly to the left. In essence, we’re observing the tail from a unique angle, obscuring its full extent.
A Celestial Celebrity: From Alien Spacecraft to Ancient Relic
Comet 3I/ATLAS has rapidly gained recognition since its discovery in July, partly fueled by speculation that it might be an alien spacecraft. However, the prevailing view among astronomers is that it’s a comet originating from an unknown star system within the Milky Way.
However, classifying it simply as a “regular” comet would be an understatement. It’s only the third interstellar visitor ever recorded, and potentially the oldest comet observed – one study suggests it could be 3 billion years older than our own solar system.
Post-Perihelion Observations: A Critical Window
The comet recently became visible again from Earth after disappearing behind the sun, reaching its closest point to our star (perihelion) on October 29. This period after perihelion is vital for astronomers, as comets are most active during this phase, providing a crucial opportunity to analyze their gaseous composition.
A Crust of Irradiated Material: A Potential Challenge
Early research hinted that the comet had endured prolonged exposure to space radiation, resulting in a thick, irradiated crust that may differ significantly from its original material. If confirmed, this “crust” could complicate the task of deciphering the comet’s origins, as scientists would be analyzing irradiated material rather than pristine components from its home star system.
Color and Brightness: Beyond the Human Eye
Zhang’s team has published preliminary research indicating that the comet rapidly brightened before perihelion, appearing noticeably bluer than the sun. The new green observation doesn’t indicate a change in color since perihelion. The term “bluer” or “redder” in astronomy refers to shorter (blue) or longer (red) wavelengths of light, and 3I/ATLAS is considerably brighter when viewed through bluer filters, although these filters incorporate a mix of green and blue light.
Accessible Observations: Even Small Telescopes Can See It
Zhang noted that the Lowell Discovery Telescope was uniquely positioned to observe the comet immediately after perihelion. However, the comet is now high enough in the sky that many larger telescopes and even small personal telescopes (with a 6-inch lens) can capture its image.
Comet 3I/ATLAS offers a remarkable opportunity to study an interstellar visitor— a relic from another star system, offering unprecedented insights into the composition of other planetary systems. Expect a flood of new discoveries in the coming months as astronomers worldwide turn their attention to this celestial wanderer.
