Scientists have long expected that we would eventually find an object in our solar system that started out orbiting another star. However, no one expected it to be so weird. The alien comet ‘Oumuamua appeared in the sky last year as it tumbled past the sun. From our limited observation time, astronomers have determined ‘Oumuamua is a small cigar-shaped object, but we didn’t know exactly how small until now. When attempting a follow-up observation with the Spitzer Space Telescope, ‘Oumuamua was nowhere to be found. So, it’s either an alien ship that engaged its warp engines or ‘Oumuamua is smaller than we thought.
Sky-watchers first detected ‘Oumuamua in the fall of 2017 using the University of Hawaii’s Pan-STARRS 1 telescope. At that point, it had already curved around the sun on its way out of the solar system. Analysis of ‘Oumuamua’s speed and trajectory confirmed it could not have originated in this solar system. Scientists have pointed to several possible home systems for the object, but we may never know where it started out.
In late 2017, NASA pointed the Spitzer telescope at ‘Oumuamua — or rather, where it should have been. That was about two months after its closest approach to Earth when it should have still been visible to the telescope. The team hoped that Spitzer’s infrared instruments would shed more light on the nature of the probable comet. However, Spitzer couldn’t spot ‘Oumuamua at all.
Previously, astronomers figured ‘Oumuamua could be as long as 2,600 feet (800 meters) along its longest dimension. However, Spitzer should have been able to spot something in that range. So, the non-detection tells us a lot about ‘Oumuamua’s actual size. Using three different models, NASA now projects the object could be as much as 1,440 feet (440 meters) in length. It could also be much smaller — just 320 feet (100 meters). The wide range comes from our uncertainty about ‘Oumuamua’s composition.
This new stat for ‘Oumuamua jives with the presumption that it’s a natural object. It’s certainly interesting to speculate that it could be an alien spaceship, but that was always an outside chance. NASA believes it’s essentially a small, low-activity comet. The perturbations in its movement are the result of gases leaking from the surface, and the newly established size supports that hypothesis.
If ‘Oumuamua holds any more secrets, they’re likely to remain that way. It will pass out of the solar system in a few years, and it’s already too far away for any telescope to see.