Only the beginning
Since the last Hubble observations in January 2018, ‘Oumuamua has been beyond astronomers’ reach. According to Meech, ‘Oumuamua should reach the Kuiper Belt in about 2024 and pass its edge in late 2025. ‘Oumuamua will pass the most distant location the Voyagers have reached in about 2038. By 2196, it will again be 1,000 AU from the Sun, although our Oort Cloud is projected to extend beyond 100,000 AU. So, when ‘Oumuamua truly passes the “edge” of the solar system, she says, depends on where you define that edge.
Although it is gone from sight, it is not out of mind. Astronomers worldwide continue to speculate on the mysteries that remain. “We really wanted to know what [‘Oumuamua] was made of. We wanted to know its chemistry. And that experiment couldn’t be done well,” Meech says. “But finally, for ‘Oumuamua, it had that very strange elongated shape. And to me, that was one of the biggest puzzles that we couldn’t solve.”
Now it appears ‘Oumuamua is not alone. On August 30, 2019, amateur astronomer Gennady Borisov at the MARGO observatory in Nauchnij, Crimea, spotted a new comet moving through the sky. Designated 2I/Borisov, it was moving at 93,000 mph (150,000 km/h), faster than expected for an object at its distance of roughly 2.8 AU from the Sun. Based on its blazing speed and its trajectory, which shows it delving into the inner solar system at an angle of 40° relative to the ecliptic plane on an orbit with a staggering eccentricity of 3.7, it too did not originate in our own solar system.
Unlike ‘Oumuamua, Borisov has a clear tail, marking it immediately as a comet. And it is still on its way toward the Sun, estimated to swing around perihelion December 8, 2019, at a distance of about 2 AU from our star. That means it’s going to get brighter before it gets fainter again, potentially reaching magnitude 15 by the time it passes closest to Earth on December 28. That’s a magnitude amateur scopes larger than 10 inches can achieve under excellent viewing conditions. Even after it fades from amateurs’ sight, professional observatories will be able to track Borisov through October 2020.
Meech’s team has already observed the object and estimates its size between 1.2 and 10 miles (2 and 16 km). They’ve already spotted CN gas coming off its surface, although the comet was still too faint in October 2019 to detect other gases, she says. But “with 2I, we have a really long observing period of a year,” Meech says. That will allow astronomers to explore its chemistry — unlike ‘Oumuamua — even if, she says, the comet’s gas and dust may hinder attempts to get a good handle on the shape and size of its nucleus. But ultimately, “[2I] looks like a comet, and it’s red, and it’s got CN.”
That means it looks very much like a typical solar system comet — and paints a very different picture of an interstellar traveler than ‘Oumuamua. But those differences are valuable for astronomers trying to learn more about how other solar systems form, whether they are like or unlike our own.
Regardless of how many interlopers we eventually see skimming through our solar system, ‘Oumuamua will always be the first. And although it’s left astronomers with outstanding questions, it also represents the beginning of an era in which we may finally unlock many of the mysteries behind how stars form their planets, and what happens to the pieces they lose along the way.