The unexpected guest showed up in our solar system about a year ago. Astronomers didn’t know much about it, but they could tell the drifting object came from beyond our solar system, making it the first such object ever discovered. They named the asteroid ’Oumuamua, and although it has long since left our solar system, scientists are still unraveling its mystery.
For instance, here’s a fact that continues to perplex astronomers: As ’Oumuamua left the solar system, it sped up a bit. This isn’t that unusual. Comets do this all the time, propelled by evaporating gases from their surface. But recent research found that ’Oumuamua isn’t a comet. So what’s pushing it to go faster?
A recent paper provides one possible answer: sunlight. A group of Harvard astronomers ran the numbers and found it was possible that the asteroid could be thin and wide enough to act like a solar sail, which raised the admittedly slim possibility that ’Oumuamua could have been manufactured that way. As in, by an alien intelligence.
(Spoiler alert: It’s not aliens. But it’s interesting to consider the possibility.)
While solar sails are an old concept, humans are just now experimenting with the basic concept. Einstein’s theory of relativity showed that light has momentum, which means satellites could use a sail to capture that momentum in much the same way as a sailboat’s sail captures the wind. Some scientists have even proposed using a solar sail to send a lightweight probe to another star.
So could ’Oumuamua be a solar sail? The Harvard researchers think it’s possible, although the asteroid would need to be extremely wide and thin. According to the paper, ’Oumuamua would need to be less than a millimeter thick in order to achieve the acceleration astronomers saw. Our solar system’s guest probably wasn’t that remarkably thin, but we actually don’t know for sure—it was spinning so fast we couldn’t get a good look at it.
As such, much of the new study is a thought experiment dedicated to proving that an asteroid hundreds of yards across and less than a millimeter thick is even capable of surviving in interstellar space. According to the paper, such an object could survive, at least for a few years. If the Harvard researchers are correct, that means ’Oumuamua is probably relatively young, and it must have come from a nearby star.
Another possibility raised in the paper is that ’Oumuamua’s solar sail is artificial, made by some alien species. The researchers admit this is highly unlikely, and it’s more reasonable to assume the asteroid formed in some strange interstellar process we haven’t discovered yet. But either way, the results from this paper mean we have a better shot at our own interstellar probes, once we finally get around to launching those.