New observations with the European Southern Observatory's Very Large Telescope (ESO's VLT) indicate that the rogue comet 2I/Borisov, which is only the second and most recently detected interstellar visitor to our Solar System, is one of the most pristine ever observed.
Astronomers suspect that the comet most likely never passed close to a star, making it an undisturbed relic of the cloud of gas and dust it formed from.
NASA Reveals Alien Composition of 2I/Borisov, 1st Interstellar Comet
When amateur astronomer Gennady Borisov discovered an interstellar comet zipping through our solar system on Aug. 30, 2019, scientists promptly turned their telescopes toward it hoping to catch a glimpse of this rare and ephemeral event.
After all, no one had ever set eyes on a confirmed comet from a foreign star system, and it was clear from its projected trajectory that the alien visitor, named 2I/Borisov, would soon disappear from the sky forever.
The comet was near its closest approach to Earth at about 180 million miles, or nearly 300 million kilometers, away.
When the scientists peeked inside the halo of gas that formed around the comet as it came closer to the Sun and its ices began to vaporize, they detected something peculiar: 2I/Borisov was releasing gas with a greater concentration of carbon monoxide (CO) than anyone had detected in any comet at a similar distance from the Sun (within less than 186 million miles, or 300 million kilometers).
2I/Borisov’s CO concentration was estimated to be between nine and 26 times higher than that of the average solar system comet.
Until more interstellar comets are observed, this result raises more questions than it answers.