When interstellar object 1I/ ‘Oumuamua was first spotted tumbling through the solar system in 2017, we’d by no means seen something prefer it. Among many unexplained oddities was its form: With a side ratio of 6:6:1, it’s principally an otherworldly pancake — not like something we’d seen in the solar system.
But it may not be in a category all by itself in any case. At the Division for Planetary Sciences assembly in October, Ari Heinze (now at University of Washington) reported preliminary outcomes for an asteroid, 2016 AK193, that behaves remarkably like ‘Oumuamua: It tumbles like the interstellar object did, and it seems to be just as elongated to boot.
But unlike ‘Oumuamua, this asteroid is not a new arrival; it has probably been going around the Sun for billions of years. Time will tell if its origins shed light on ‘Oumuamua’s mysteries.
A Shape Analog
Astronomers noticed ‘Oumuamua as it was speeding out of the solar system (it had already swung around the Sun when they spotted it), and its wildly varying brightness immediately indicated two strange things: First, it was tumbling, rather than spinning around an axis. Second, its shape was surprisingly stretched out.
The shape was a puzzle because until that point, the most elongated asteroid that astronomers had observed was 216 Kleopatra, which has the shape of a dog bone (it’s in all probability a contact binary), with a side ratio of three:1.
However, when Heinze added measurements of 2016 AK193, taken utilizing the Gemini Observatory in 2020, to some days of observations taken again in 2016, he realized that what he had discovered was a tumbling object roughly the identical dimension as ‘Oumuamua, and possibly as elongated, too.
“‘Oumuamua was a huge mystery because there has literally never been anything like that seen before,” says Darryl Seligman (University of Chicago), who was not involved in the observations. “So if there’s anything that’s close to that in the solar system, just from that standpoint, it’s worth following up.”
Follow-up will take some patience, though — 2016 AK193 is a near-Earth object, but that doesn’t imply it’s close to Earth always. It gained’t come shut sufficient to watch once more till 2029, Heinze says. When it does, it’ll method inside 0.05 astronomical unit of Earth, showing at about 18th magnitude.
“Hopefully there will be some detailed studies then (e.g., radar imaging plus lots more photometry),” Heinze says, “but there is very little prospect for additional useful measurements in the intervening seven years.”
Same Shape, Different Age
Still, the asteroid’s mere existence is intriguing, as a result of it is from interstellar — it has in all probability been in the solar system for billions of years. ‘Oumuamua, on the other hand, is more likely young, less than 100 million years old based on its incoming trajectory.
“’Oumuamua’s age is subtly the weirdest factor,” Seligman says. Objects in the galaxy orbit its heart, and the older an object is, the extra seemingly it’s to have gravitationally ricocheted off one other object, out of the galactic plane. ‘Oumuamua, though, came in almost exactly along the galactic plane, which means that any theories on its nature and origin have to also explain its youth.
That’s partly why many explanations of ‘Oumuamua have focused on exotic ices: Seligman has himself speculated it was made of hydrogen ice, recently tossed out of an interstellar cloud. Others have suggested it was made of nitrogen ice, chipped off a Pluto-like body. Harsh sunlight would ablate such ices like a bar of soap in the shower, Seligman says, reshaping the body into a mere sliver of its former self.
It’s additionally attainable the object comprises extra mundane carbon monoxide ice, like distant solar system objects and like 2I/Borisov, the second interstellar object. Observations didn’t catch a coma round ‘Oumuamua, but as Seligman points out, “Comets turn on and off all the time.” But carbon monoxide ice doesn’t ablate as rapidly, so this state of affairs doesn’t clarify the form as effectively, he provides.
Future observations of 2016 AK193 will assist put such concepts to the check. Its present near-Earth orbit is unstable, Heinze notes, and can solely final some 100 million years. It’s attainable this object used to belong to the principal belt earlier than a gravitational encounter redirected it, and that nudge would possibly even have precipitated its reshaping. More and higher observations will assist us perceive its previous.
While 2029 could seem a very long time to attend for follow-up, it’s higher than what we’ll get from ‘Oumuamua. It’s already effectively on its way out of the solar system, and it’ll move Neptune’s orbit subsequent year. As of but, no single principle explains all our observations of this object. A solar system analog could be the closest we are able to get.