The first-ever detection of an asteroid from beyond the solar system revealed a remarkable object. About 400 meters long and only 40 meters wide, 'Oumuamua's axis ratio of 10:1 makes it the most elongated asteroid ever discovered. The highest axis ratio we see for asteroids in the solar system is only about 3:1. The odd shape is perhaps a clue about when the asteroid was flung from its own star during the formation of that solar system, or perhaps it can tell us something about what happens to space rocks when they fly through interstellar space for millions of years.
And of course there is another remote possibility. Perhaps, just maybe, the object is elongated because it is artificial, the equivalent of a rocket booster or a probe from an advanced extraterrestrial species. Fortunately for the believers, Yuri Milner and Breakthrough Listen are going to point the largest fully-steerable radio telescope in the world, the 100-meter Green Bank Telescope, at the object, which is currently about twice as far away from Earth as the sun.
Avi Loeb, a professor of the Harvard-Smithsonian Center for Astrophysics (CfA) who has written multiple papers on the search for extraterrestrial life, first brought the unique properties of the object to Yuri Milner's attention, suggesting the object could be artificial.
"This is the first interstellar object to be discovered and its axis ratio is so extreme. Therefore when I first learned about it I started wondering whether it might be an artificially-made probe which was sent by an alien civilization," Loeb wrote in notes about the early observation of 'Oumuamua provided to Seniorhelpline. He goes on to point out that the "Keplerian orbit" of the object, meaning its trajectory can be explained with just the gravitational encounter of the sun, makes it unlikely that the object is a controlled space probe. "Most likely, this is just a large rock, but it is worth checking for any radio signal to be sure."
The GBT observations of 'Oumuamua, which is Hawaiian for "scout," will be valuable to astronomers even if the object turns out to be nothing more than an asteroid. In the first observations, the interstellar rock did not appear to have a cloud of debris following it known as a coma, which suggests it does not have any water ice. The GBT radio observations should be able to determine more accurately whether or not the object has any ice or surrounding debris.
"Thus far, observations have focused on natural emission (looking for water, led by the Jet Propulsion Lab) or been restricted to engineering tests to establish our ability to target the object," Andrew Siemion, director of the SETI Research Center at the University of California Berkeley, said in an email to Seniorhelpline. "The upcoming observations will be more sensitive and more complete, allowing us to search for a wide variety of signals over more than 10 GHz of the radio spectrum."
Based on the changing brightness of the light reflected by 'Oumuamua, astronomers have determined that it rotates around its axis about every eight hours. The Breakthrough Listen observations will capture each side of the interstellar object to give us the best idea of what it's made of, and perhaps a clue as to where it came from, be it mothership or neighbor star.