A quick visit from ‘Oumuamua

The first known interstellar object to visit our solar system came and went in a hurry, and didn’t give astronomers much time for observations. The strange ’Oumuamua was first discovered when it zipped past Earth in October, and by December it was already way too faint to see. Gregory Laughlin, astronomy professor from Yale, gave a plenary talk about ‘Oumuamua at the recent meeting of the American Astronomical Society held in Seattle.

Gregory Laughlin

Gregory Laughlin, astronomy professor at Yale, gave a talk about ‘Oumuamua Jan. 7 at the 233rd meeting of the American Astronomical Association, held in Seattle. Photo: Drew Dettweiler.

About a half dozen observatories collected data about ‘Oumuamua as it sped through the inner solar system at 26 km/sec. Laughlin said they computed a highly eccentric path that indicated that the object came from beyond our solar system. Spectra of ‘Oumuamua found it to be red and featureless. Much of the other stuff in the outer solar system, such as trojan asteroids, Kuiper Belt objects, and moons of other planets also are reddish.

“The immediate inference is that ‘Oumuamua is some kind of reddish, icy, volatile-rich body from another planetary system,” Laughlin said, “something that’s been ejected and which has traveled through space for a long time, and which has happened to encounter the solar system.”

Laughlin noted that there are a number of strange attributes of ‘Oumuamua. Even though it passed close to the Sun, there was no sign of coma, so there was no or very little fine dust on ‘Oumuamua. It has an odd period light curve that varies in magnitude by three in the space of hours, and that’s a lot. It suggests that ‘Oumuamua is monolithic. It was accelerating as it headed out of the solar system, a fact discerned because its path wasn’t a good match for a Keplerian orbit. The acceleration indicates there must be some sort of outgassing, but ‘Oumuamua didn’t exhibit the chaotic sort of tumbling usually associated with that. Instead, the object’s jet may swing it back and forth like a pendulum.

“We think that the acceleration, the rotation, and the chaotic light curve are all reasonably in match,” Laughlin noted. “There’s lots of mysteries with ‘Oumuamua, but it doesn’t appear that there’s anything completely crazy.”

Laughlin looks forward to a time when our observing tools are more sensitive and we can hunt down other such objects in interstellar space.

“‘Oumuamua’s presence is signaling a vast population of unseen planets,” Laughlin said. He figures there may be about 1026 such objects in the galaxy. For ‘Oumuamua, he said the likelihood of getting close to another star is about once every 1014 to 1015 years.

“Those brief, exciting moments in September and October were wonderful for us, but they were really the time of ‘Oumuamua’s life,” he said.

Hawaiian names for astronomical objects

The relationship between astronomy and Hawaii has not always been a happy one. Witness the legal squabble about the construction of the Thirty Meter Telescope at Mauna Kea, which was just settled in court last fall. But there’s been a thaw in this cold war according to Ka’iu Kimura, executive director of the ‘Imiloa Astronomy Center in Hilo, Hawaii.

“I participated in ‘Imiloa from its very inception in an attempt to bring about collaboration between the indigenous and scientific communities,” Kimura said before Laughlin’s lecture. She recalled that the effort was hardly a collaboration at first, but sharing a space helped, and now they’ve arrived at an agreement that respects both sides.

“Major astronomical discoveries from both Haleakala and Mauna Kea are being given Hawaiian names, honoring Hawaii as a place of discovery and of profound knowledge,” Kimura said, adding that a name isn’t just what something or someone is called.

“A name represents the identity and gives insight to that someone or something’s origins and connections to others, and for Hawaiians this ancient practice affirms Hawaii’s ongoing contribution to global astronomical advancement.”

The name of our recent visitor was largely created by Larry Kimura, Ka’iu’s uncle and a professor of Hawaiian language and Hawaiian studies at the University of Hawaii, Hilo.

“We loosely translate ‘Oumuamua to mean a scout or messenger from the deep, distant past,” Ka’iu said. Future objects will be named by a working group that includes astronomers, indigenous Hawaiians, educators, and community leaders. Kimura believes that the collaboration builds deeper appreciation and creates a shared sense of ownership in the outcomes.

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Further reading: Our article about ‘Imiloa (PDF) in the December 2007 issue of the Seattle Astronomical Society newsletter.

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