A Second Interstellar Visitor Is Approaching Our Solar System

In 2017, an interstellar object named ‘Oumuamua shot through our own solar system. It was the first time we’d ever detected an interstellar object passing through the solar system, and its unusual shape recalled the artificial vessel in Arthur C. Clarke’s Rendezvous with Rama science fiction novel. Now, an amateur Ukrainian has spotted an object zooming through our solar system that’s been confirmed as a comet — and one unlikely to be captured by the sun.

Comet C/2019 Q4 (Borisov), discovered by Gennady Borisov, is probably our second interstellar visitor after ‘Oumuamua. Scientists can already detect the coma — the fuzzy trail of ice and dust that spins off the comet as it approaches the sun and begins to melt. And unlike ‘Oumuamua, C/2019 Q4 is still on approach to Earth. While it won’t get closer than 180 million miles, it won’t reach that point until December 7. We’ve got more time to observe this ancient visitor, and there are hopes that we may detect clues about its origin from the coma of debris it sheds. We didn’t detect ‘Oumuamua until it was already on its way out of our solar system, but C/2019 Q4 (Borisov) got picked up on earlier approach.

“This is the first highly active object that we’ve seen coming in from something that formed around another star,” Michele Bannister, an astronomer at Queen’s University Belfast, told National Geographic.

We should be able to monitor C/2019 Q4 for a year as it makes its way into and out of the solar system. The eccentricity of C/2019 Q4 suggests that it’s a one-time visitor to our solar system. While comets can exist on the outside of the solar system until nudged into orbits that fling them sunward, the eccentricity of these orbits tends to be low. According to Davide Farnocchia, of NASA’s Center for Near-Earth Object Studies at JPL:

The comet’s current velocity is high, about 93,000 mph [150,000 kph], which is well above the typical velocities of objects orbiting the sun at that distance. The high velocity indicates not only that the object likely originated from outside our solar system, but also that it will leave and head back to interstellar space.

Comets like C/2019 Q4 aren’t really unique — there are an estimated 10,000 pieces of interstellar debris in orbit between here and Neptune at any given time — but this material is tiny and extremely difficult to see. Identified pieces of incoming interstellar objects are far rarer. We don’t have detailed photos of the comet yet because the current nucleus is so small, between 1.2 – 10 miles in diameter. It should be visible with mid-powered telescopes through April 2020, but will only be observable with professional telescopes after that date. By October 2020, C/2019 Q4 should fade from view — assuming, of course, that it isn’t something altogether different.

Remember: The Ramans do everything in threes.*

* – But seriously, it’s just a comet.

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