Astronomers have spotted a comet that appears to have come from outside our solar system, which would make it the second interstellar object we’ve detected. Plus, it’s headed toward Earth, which will make it easier to study than the previous interstellar rock. It will approach Earth in December, but will get nowhere near close enough to hit us.
The first interstellar object, called ‘Oumuamua, was an asteroid discovered in October 2017. When we spotted it, it was already on its way out of the solar system and moving so fast that it was difficult to study, so it remains somewhat mysterious.
This new comet was spotted in images from the Crimean Astrophysical Observatory on 30 August, moving on an orbit that appears to indicate that it came from beyond our solar system, from the direction of the constellation Casseiopeia. It has not been named yet, and is currently referred to as gb00234.
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In the days since the comet’s discovery, astronomers at 20 observatories have taken more than 150 pictures of gb00234 to attempt to nail down its path more precisely. So far, the trajectory of the comet is not yet set in stone, and astronomers are far from certain that it is actually interstellar.
“We had one like this in late May and it turned out to be a normal comet,” says Michele Bannister at Queen’s University Belfast. We don’t have enough data yet to know whether gb00234 came from outside our solar system, she says. “It’s a bit underbaked as yet.”
Observations over the next few days should make the comet’s path more certain and clarify whether it is truly interstellar. Bill Gray, who develops astronomy software, modeled the path and found that unless a large portion of the early data is incorrect, it’s difficult to explain without unexpected forces acting on the comet. Some comets start to evaporate as they near a star, which can create propulsion that changes their speed.
“It’s either really a bright interstellar comet, or it’s getting pushed around a lot by non-gravitational forces,” Gray says. “Both are a little hard to believe, and we’ll probably have to wait for more data.” If it is an interstellar comet, suggests that it is heading toward us at about 30 kilometres per second and will pass Earth in December at a distance less than twice that of Earth’s distance from the sun.
This comet was caught much earlier in its journey through the solar system than ‘Oumuamua, which will make it easier to observe in detail as it passes Earth. If it turns out to be truly interstellar, it will present a unique opportunity to study a rock from around another star and perhaps learn about what other solar systems are like.
