Further observations of ‘Oumuamua revealed it carried no traces of water ice, which suggests the asteroid is made of rock or perhaps metal. Whatever it is, the material is certainly sturdy. ‘Oumuamua rotates about every seven hours, a rate that would likely cause some rocky objects, nicknamed “rubble piles,” to crumble. ‘Oumuamua even survived a close pass with the sun in September, before it was detected, without breaking apart.
Thanks to its nonspherical shape, the asteroid is tumbling uncontrollably. “If you take an object that isn’t round and you throw it up in the air, it’ll make this complicated spinning motion,” said Jason Wright, an astronomer at Penn State University. “It just doesn’t just spin nicely along one axis.” Wright said a long journey across the cosmos can slow an object’s tumbling, but ‘Oumuamua has shown no signs of stopping its spinning.
“I’m not saying that any of that is necessarily a smoking gun or super exciting,” Milner said of ‘Oumuamua’s unusual properties. “But I think it warrants thorough investigation from a SETI standpoint.”
Karen Meech, an astronomer at the University of Hawaii Institute for Astronomy whose team discovered ‘Oumuamua, has said their observations are “entirely consistent with it being a natural object.” Analysis of the light reflected by the asteroid shows ‘Oumuamua is red, a color that would be expected for rocky bodies exposed to the cosmic radiation of interstellar space for long periods of time.
There are indeed some natural explanations for some of ‘Oumuamua’s weird properties. Some astronomers say ‘Oumuamua could be a contact binary—two objects that drift closer until they touch and fuse at one end—like our solar system’s Kleopatra, a metallic, dog-bone-shaped asteroid.
They suggest any ice on the asteroid’s surface was zapped away by high-energy particles on its journey between stars. Perhaps the asteroid is so hardy because it formed in the inner regions of a solar system, where rock and metal are more commonly found than ice. This would be tricky, since most exoplanets discovered so far orbit extremely close to their parent star, preventing them from flinging debris beyond the star’s pull. But they may have siblings, like our Jupiter and Neptune, lurking in the darkness, doing the work for them.
If ‘Oumuamua has anything exciting to tell us, it’s that our understanding of planet formation needs some work, said Gregory Laughlin, an astronomer who studies exoplanets at Yale University.“We know that planetary systems are extremely common, but the way that their process unfolds seems to be richer than anticipated,” he said.
* * *
The thought of a spaceship being dropped into planetary systems like a reconnaissance mission may sound like the stuff of science fiction. But for Milner, it’s the future. Milner is spending $100 million over 10 years to develop spacecraft technology capable of sending a tiny probe hurtling at one-fifth the speed of light toward Alpha Centauri, the nearest star system to Earth. If Milner succeeds, the 25-trillion-mile trip would be cut from tens of thousands of years, based on our current technology, to a breezy 20 years. Hundreds of these miniature probes would be deployed into the darkness in the hopes that at least one might complete the journey. Perhaps another civilization already had the same idea.