Following a speedy yet far-reaching analysis, University of Hawaii astronomers Monday unveiled a description of their discovery last month of the first interstellar object seen passing through our solar system.
“This thing is quite strange,” said Karen Meech of UH’s Institute for Astronomy and lead author of the study, which appeared Monday in the journal Nature.
The rapidly rotating interstellar asteroid — or more than eight football fields in length — is a highly elongated shape rarely, if ever, seen in our solar system.
At the same time, the dark red to muddy brown color and other characteristics suggest it shares similarities to space objects occurring in our solar system naturally.
After consulting with UH-Hilo Hawaiian language experts Ka‘iu Kimura and Larry Kimura, the UH team named the interstellar visitor ‘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.
In anticipation of similar discoveries, the center adopted a new designation for such objects. An “I” for interstellar will be included in the identifying scientific code name. Correct forms for referring to this object are 1I, 1I/2017 U1 and 1I/‘Oumuamua.
The mysterious object was discovered Oct. 19 by UH researcher Rob Weryk using the university’s Pan-STARRS telescope at the summit of Haleakala.
Weryk wasn’t sure about the find at first, but the highly unusual orbit suggested this was something out of this world.
By the time its exaggerated orbit was confirmed, however, ‘Oumuamua was already rapidly traveling away from the sun and Earth and heading out of the solar system. That left researchers scrambling to conduct their observations.
“I was sleeping in my office, working 17-hour days and writing proposals for telescope time,” said Meech, who specializes in small bodies and their connection to solar system formation.
Officials said the UH team was already prepared to leap into action for discoveries that might come from Pan-STARRS, a panoramic survey telescope operated by the university and funded by NASA. Now they are the first to publish their results.
The team gathered data from telescopes around the world, including the Canada-France-Hawaii Telescope, the United Kingdom Infrared Telescope and the Keck Telescope on Mauna Kea, as well as the Gemini South telescope and the European Southern Observatory’s Very Large Telescope in Chile.
Combining the power of all of the telescopes, astronomers said they were better able to recognize ‘Oumuamua’s peculiar personality.
One thing that stood out was the dramatic and even “bizarre” change in brightness as the object traversed the sky, Meech said.
“When I first saw the light curve, I said, ‘Wow, you never see light changing this big,’” she said.
The changing brightness suggested that the object was rotating and catching reflective light. With the object spinning every 7.3 hours, the researchers calculated the object at more than 10 times longer than it is wide, something never seen in our solar system, Meech said.
According to the paper, the object is inert, without a hint of dust around it. ‘Oumuamua is likely to be dense, possibly rocky or with high metal content. It is unlikely to have any water or ice, and its surface may be dark and reddened due to the effects of irradiation from cosmic rays over millions of years.
Meech said ‘Oumuamua’s surface is consistent with comets or organic-rich asteroid surfaces found in our own solar system. Its surface resembles the dark-bodied and reddish Trojan asteroids, which share Jupiter’s orbit around the sun, and Saturn’s Iapetus moon and its slightly reddish-brown coloring.
Where did the visitor come from?
Preliminary calculations suggest that it was traveling from the direction of the star Vega, in the northern constellation of Lyra. However, according to the paper, even with ‘Oumuamua traveling at nearly 60,000 mph, Vega wasn’t even near its current position when the asteroid was there about 300,000 years ago.
It’s possible, astronomers said, ‘Oumuamua may have been traveling through the Milky Way as a free agent, unattached to any star system for hundreds of millions of years, before it just happened to make an appearance in our neighborhood.
The paper estimates that an interstellar asteroid similar to ‘Oumuamua passes inside the orbit of Earth several times a year.
The problem is they are faint and hard to spot, astronomers said, and it is only recently that survey telescopes, such as Pan-STARRS, are powerful enough to have an opportunity to find them.
Help is on the way, however. Upgrades to survey instruments and new technology mean more interstellar objects could be spotted in the coming years.
Chile’s Large Synoptic Survey Telescope, under construction and nearing completion, is expected to be the largest survey telescope in the world.
“With any luck, we should eventually find more,” Weryk said.
Olivier Hainaut of the European Southern Observatory in Garching, Germany, said astronomers will continue to track and observe ‘Oumuamua.
“We hope to more accurately pin down where it came from and where it is going next on its tour of the galaxy,” Hainaut said in a release. “And now that we have found the first interstellar rock, we are getting ready for the next ones.”