Mankind knows of two objects that have entered our solar system from different star systems. Although there may have been—and still be—many more such objects which have entered and exited our solar system since time immemorial, we are currently aware of two such objects.
One—the first—interstellar object we spotted was ‘Oumuamua, discovered by Robert Weryk using the Pan-STARRS telescope at Haleakala Observatory. The cigar-shaped object was discovered in October 2018, some 40 days after it made its closest approach to the sun.
Estimate to be between 100 and 1,000 meters (330 and 3,280 ft) long, the curious interstellar object created a major buzz in the scientific community, and some experts even suggested that the oddly-shaped object may be of alien origin, in other words, that the object itself was not made in nature, but sent out by an advance alien civilization to monitor our solar system.
Eventually, this notion was rejected and the world quickly forgot that such a mysterious object even entered our solar system in the first place. That was until another similar object was found by astronomers. Originally designated C/2019 Q4 (Borisov), this is the first observed interstellar comet and the second interstellar object after ‘Oumuamua.
With a heliocentric orbital eccentricity of 3.36, the interstellar visitor is not bound to the sun. The comet made its way through the ecliptic of the solar system in October 2919, making its closest approach to the sun on December 8, 2019, as it passed just over 2AU from the star.
The object was studied by astronomers from Yale University who explained that the comet—including gits tail and coma—was 14 times the size of Earth, stating how “it’s humbling to realize how small Earth is next to this visitor from another solar system.”
Only rough estimates of the exact size of Borisov are available, mostly because its nucleus is hidden by its come. Estimates, however, suggest that the diameter of 2I/Borisov’s nucleus ranges from 2 to 16 km.
Explosions on 2l/Borisov
As it moves away from the Sun, the comet, discovered by Russian astronomer Guennadi Borisov, was seen hurling material at two consecutive events recorded between March 4-5 and March 8-9.
On the first occasion, the object became brighter by a 0.3 magnitude, and on the other occasion by a magnitude of around 0.4, the two “explosions” followed by an almost constant brightness.
The total increase in brightness registered was, therefore, approximately 0.7 magnitudes in 5 days. Both outbursts show that the comet is disintegrating, something that astronomers from the universities of Warsaw and Jagiellonian (Krakow) concluded after observing the phenomenon in infrared light through the Las Campanas Observatory, located in Chile’s Atacama Desert.
“This behavior is strongly indicative of an ongoing nucleus fragmentation,” the scientists revealed in a statement published top the Astronomers Telegram.
(This animation records what the comet looks like when emphasizing the coma very near the nucleus versus the fainter but more extended comet tail.)
As explained by astronomers, long-period or dynamical new comets come from places very far in the solar system—like the Oort Cloud—and are more likely to break up compared to short-period comets.
What we know so far about 2l/Borisov—based on the color and composition—suggests that it is extremely similar to long-period comets, which means that disintegration caused by heating from the sun was likely, albeit not guaranteed.
However, the recent observations and increase in brightness confirm the comet is exploding and disintegrating. As the object disintegrates, astronomical observations will allow scientists to understand its spectrum and help reveal its internal chemistry as well as its nucleus.