Interstellar intruder long gone but still offering surprises

‘Oumuamua, the mysterious space object that rocked the astronomy world last fall after it was identified as a visitor from another star system, is now roughly 600 million miles away from the Earth and getting more distant by the second.

Will we ever see it again?

“Never,” says Karen Meech, an astronomer at the University of Hawaii’s Institute of Astronomy, who helped lead an international team of scientists studying the interstellar intruder first seen from Hawaii. “It was a one-way trip. It came in and it’s gone out. It’s now 5 billion times fainter than the naked eye can see, and it’ll never get any brighter.”

Even though it was a quick pass through our solar system, ‘Oumuamua’s legacy is secure as the first confirmed object from a distant galaxy to visit our solar system.

It also continues to offer a few surprises, according to a new study, co-authored by Meech and her European and UH colleagues. The researchers discovered that ‘Oumuamua experienced an unexpected boost in speed and shift in trajectory as it passed through the inner solar system.

The finding, outlined in the latest edition of the journal Nature, led the team to conclude that the object is a comet rather than the asteroid it was originally classified as.

The speed boost and trajectory shift are consistent with the behavior of a typical icy and dusty comet that has jets of gaseous material expelled from its surface, according to the paper.

The problem, according to Meech, is that there were no outward signs of such “outgassing” from ‘Oumuamua. The object didn’t display any signs of an atmosphere or tail like a comet.

The researchers estimated that ‘Oumuamua’s outgassing may have generated only a small amount of dust — enough to give a speed boost but not enough to be detected.

Meech suggested that the small dust particles found on the surface of most comets previously eroded away during ‘Oumuamua’s long journey through interstellar space.

The mysterious object was spotted Oct. 19 by UH researcher Rob Weryk using the university’s Pan-STARRS 1 telescope at the summit of Haleakala. Weryk wasn’t sure about the find at first, but the highly unusual orbit suggested it was something from outside the solar system.

After Weryk’s suspicion was confirmed, the discovery set off a flurry of scientific research, with telescopes around the world locked in on the strange object, which by then was zipping away from the sun and on its way out.

The object, wobbling like a top and possibly reddish in color, was described as being a half-mile long and narrow — possibly cigar- or flattened-oval shaped — with an axis ratio of 10 to 1.

“There’s nothing in the solar system that looks like this,” Meech said. “Only a handful of objects have an axis ratio of 5 to 1.”

Because it was discovered in Hawaii, scientists consulted with UH-Hilo Hawaiian language experts Ka‘iu Kimura and Larry Kimura, who named it ‘Oumuamua, which means leader or scout.

The name “reflects the way this object is like a scout or messenger sent from the distant past to reach out to us,” according to an announcement by the Small Planet Center, the International Astronomical Union outfit charged with naming things in space.

When news of the strange visitor came out, there were more than a few folks who wondered if it could be an alien spaceship or satellite.

Meech said she and the other scientists who studied the object strongly believe it is natural, probably some type of debris created during the messy birth of a planet or violent death of a star. It may well have been tossed out of its own solar system to wander through interstellar space like “celestial driftwood,” she said.

But Meech conceded that scientists were unable to prove the object wasn’t artificial. The reddish color, odd shape and tumbling motion could all have different explanations, she said.

For what it’s worth, however, the Breakthrough Listen initiative deployed West Virginia’s Green Bank Telescope in an effort to detect any radio signals beaming from the object. Nothing was heard.

With ‘Oumuamua long gone, scientists are now left to sift through the accumulated data. Meech said she still plans to look at images collected from NASA’s Hubble Space Telescope showing ‘Oumuamua’s path going back in time. The idea is to figure out which star system it may have originated from.

Unfortunately, the findings of the Nature study mean that it’s going to be harder to figure out, she said. ‘Oumuamua’s nongravitational motion — or shifting trajectory and speed — adds a greater degree of uncertainty to the calculating of its place of origin.

“We may never know where it came from,” she said.

But Meech said she’s confident there will be more interstellar objects to be seen as upgrades to survey instruments and new technology increase opportunities for viewing vast sections of the sky.

The Pan-STARRS 2 telescope just started its survey from Hawaii, she said, while Chile’s Large Synoptic Survey Telescope, under construction and nearing completion, is going to be an even larger survey telescope.

“We would have missed it had it not come so close,” Meech said of ‘Oumuamua, adding that there are undoubtedly more interstellar objects out there.