First it was an asteroid, then a comet and now a group of Harvard researchers suggest the enigmatic ‘Oumuaua could be an alien-built light sail. The half-mile-long flying whatever-it-is was discovered on October 2017 with the Panstarrs-1 telescope on Mt. Haleakala in Maui. Like similar discoveries, the object was too small to appear any larger than a point of light like every other asteroid. And that’s exactly what astronomers though it was — at first. Then it began exhibiting weird, comet-like behavior. Let’s examine what makes ‘Oumuamua so unusual:
- It came from outside the solar system because of its extremely high speed of 196,000 mph (87.3 km/sec). Objects bound to the solar system don’t travel that fast except for a brief time when they’re very close to the sun. Mercury, the fastest moving, races along at a comparatively leisurely 48 km/sec. Some asteroids and comets get much closer to the sun than that and travel at faster speeds but only for a short time.
- Its orbit was hyperbolic. In other words, it wasn’t a closed loop but completely open-ended. Instead of following an elliptical path and returning to the sun time and time again, ‘Oumuamua’s orbit was a hyperbola — inbound, outbound and gone!
- Its dramatic variations in brightness over time suggested it was highly elongated, possibly up to 10 times as long as wide. The object also tumbles in two different ways: end over end and around another axis, making one complete rotation every 7.3 hours.
- It doesn’t look like a comet but behaves like one. Heat from the sun vaporizes comet ice to form jets made of gas and dust. As the material shoots away from the comet, it kicks back against it, changing the object’s speed. As ‘Oumuamua left the vicinity of the sun, instead of slowing down, something made it speed up yet no jets, dust or gas were detected.
Shmuel Bialy and Abraham Loeb, with the Harvard Center for Astrophysics, took a broad look at the problems posed by the object and concluded it was possible that the observed increase in speed is the result of solar radiation accelerating a large, thin sheet of material through space. Their calculations show that such an object could survive even after traveling more than 16,000 light years even after getting pinged by dust grains and twisted about by gravitational stresses along the way.
In other words, they consider possibility that it might be a light sail of artificial origin, propelled by the light of the sun on a potential reconnaissance mission of the our solar system. Did I just write that? They admit it’s speculative but are at a loss to find a better explanation.
A solar or light sail is a large, thin sheet of reflective material that’s propelled by nothing more than the pressure of light from the sun or a nearby star. When first unfurled, it moves very slowly but gradually accelerates as the “push” of light accumulates over time. Light sails might be a routine way for an advanced civilization to explore their galactic neighborhood. To improve the chances one would pass close enough to a star with planets, many such sails would have to be deployed for one or two to hit the mark. Like a thousand dandelion seeds scattered by the wind, only a few fall on fertile ground.
Not only does sunlight on a sail neatly explain the peculiar acceleration we see, but the light from a sail would vary depending on how it tumbled along with changes in our viewing angle, mimicking the ups and downs in ‘Oumuamua’s brightness. If it were a mission by another civilization, we might expect to pick up an electrical signal or some sort of radio transmission from the object. Then again, maybe the batteries have failed.
Today, the object is nearly 3 billion miles from Earth and too faint to see anymore. As it slips ever further into darkness, it’s important to remember that extraordinary claims require extraordinary evidence. While the light sail concept may be plausible, we know so little about the object that it could be something else entirely or something familiar acting in an unfamiliar way. Consider that the less you know about a thing, the more ways there are to imagine it.
While it’s a valuable exercise to consider an artificial origin, we need to be cautious in assuming complete knowledge of common objects like asteroids and comets before we discount a natural explanation. Even if ‘Ourmuamua isn’t artificial, the fact that it’s “not from around here” is remarkable enough. Its discovery has opened our eyes and will inspire searches for more of its kind.
For more information, take a look at the original research paper.