The astronomer who discovered the second interstellar comet to visit Earth’s neighborhood described how he came across the mysterious space rock, which recently made its closest approach to the Sun.

The interstellar object, dubbed as 2I/Borisov, was named after Gennady Borisov, an astronomer from Crimea. Borisov first came across the object in August earlier this year. After analyzing the trajectory of the object, international organizations classified 2I/Borisov as an interstellar comet, which means it came from a different star system.

According to Borisov, he wasn’t particularly looking for something in the sky when he first discovered the interstellar comet. Instead, he carried out his usual asteroid-hunting activities, which take place at night.

As he was going through his observations, he came across a photo that contained a strange object. He noted that the object immediately caught his attention.

“The observational shooting went on at night until predawn. In the morning, astronomers usually catch up on sleep after the night of observations,” he told Space.com.

“Later that day, I started processing the observations, and in the evening, while reviewing the last portion of photos, at the very edge of a picture, I saw an object that caught my attention, as it wasn't listed in the catalog,” he added.

At first, Borisov wasn’t sure if the object he spotted through his telescope was a comet or if it came from a different solar system. But, after submitting his findings to the International Astronomical Union, the object was eventually classified as an interstellar comet.

Currently, 2I/Borisov is making its way through the Solar System. On Dec. 8, the comet reached its closest point to the Sun, according to Earth Sky. It flew past the massive star from a distance of 2 astronomical units, which is equivalent to almost 200 million miles.

As it moves across the Solar System, the comet is expected to make its closest approach to Earth on Dec. 28. 2I/Borisov is expected to be about 500 million miles from Jupiter by mid-2020. Astronomers predict that by this time, the interstellar comet will be exiting the Solar System. It could take millions of years before it enters another system.

2I Borisov
NASA's Hubble Space Telescope has given astronomers their best look yet at an interstellar visitor — comet 2I/Borisov — whose speed and trajectory indicate it has come from beyond our solar system. NASA, ESA and J. DePasquale (STScI)
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