After a year of analysis, the SETI Institute has concluded that 'Oumuamua, the first interstellar object known to have visited our Solar System, isn't trying to make radio contact with us. Using the Allen Telescope Array (ATA), a team of scientists led by Gerry Harp monitored the visitor between November 23 and December 5, 2017 when it was about 170 million mi (274 million km) away. Later analysis showed that it's not the source of any artificial radio signals.

When something like 'Oumuamua appeared in our neighborhood, it was bound to spark a kind of interest different from any previously discovered object. First seen on October 19, 2017 by the University of Hawaii's Pan-STARRS 1 telescope, 'Oumuamua was soon discovered to be on an open-ended hyperbolic trajectory that had already brought it to within 0.25 AU (23 million mi, 37 million km) of the Sun in September.

In other words, 'Oumuamua came from outside of the Solar System and was speeding back into deep space at 59,000 mph (95,000 km/h).

Even on the blandest scientific level, 'Oumuamua raised all sorts of questions. What was it? How big was it? Was it an asteroid or a comet? What did it consist of? Where did it come from? Where was it going?

But there was one outlier of a question that 'Oumuamua posed, which scientists took very seriously. Did it come here accidentally, or was it deliberately aimed at our system? In other words, was it an artificial probe deliberately sent from another star?

It may sound like science fiction, but there were good reasons for considering the possibility. The mere fact that it was passing through the inner Solar System indicated that it could be on some sort of flyby mission. Also, it had a long spindle shape and was devoid of the typical comet's coma. In addition, the pressure from the sunlight hitting it was causing slight changes in its orbit. This caused some Harvard scientist to speculate that it might be equipped with a solar sail.

The SETI Institute and the Breakthrough Listen initiative reasoned that if 'Oumuamua was some sort of artificial probe, it would very likely be transmitting radio signals that were either directed at us, broadcast in every direction, or were simply emitted as part of the hypothetical spacecraft's general operations.

SETI's 12-day observations while 'Oumuamua was still relatively close to Earth were made using ATA's wide-band correlator at frequencies between 1 and 10 GHz and with a frequency resolution of 100 kHz. ATA is capable of detecting an omnidirectional transmitter onboard the object, at powers as low as 30 to 300 milliwatts. According to the Institute, this is very low, with artificial satellites normally transmitting at up to 10 watts.

SETI says that ATA detected no signals from 'Oumuamua, but this negative result is still useful because it not only limits the possibilities of what the object is, but can also act as a guide for studying future interstellar visitors or even objects inside the Solar System.

"We were looking for a signal that would prove that this object incorporates some technology – that it was of artificial origin," says Harp. "We didn't find any such emissions, despite a quite sensitive search. While our observations don't conclusively rule out a non-natural origin for 'Oumuamua, they constitute important data in accessing its likely makeup."

The research was published in the journal Acta Astronomica.