Hawai‘i Astronomer: First Interstellar Visitor is ʻVery Strange’

Artistʻs impression of `Oumuamua, the first interstellar object ever detected in our Solar System. This unique object was discovered on October 19, 2017 by the Pan-STARRS 1 telescope in Hawai`i. Subsequent observations from Gemini, ESO’s Very Large Telescope in Chile, CFHT, UKIRT, and other observatories around the world show that it was on a path which must have been traveling through interstellar space for millions of years before its chance encounter with our star system. Credit: ESO/M, Kornmesser.

Astronomers at the University of Hawai‘i at Mānoa’s Institute for Astronomy (IfA) made a stunning discovery in October 2017. Using the Pan-STARRS1 telescope on Haleakalā, researchers observed the first interstellar object seen passing through our Solar System.

“This thing is very strange,” said IfA Astronomer Karen Meech, who led an international team that made detailed measurements of the object.

Originally referred to as A/2017 U1 (with the “A” for asteroid and the “I” for interstellar), the oblong object was officially named ‘Oumuamua with guidance from UH Hilo Hawaiian language experts Kaʻiu Kimura and Larry Kimura. The name characterizes the object as a scout or messenger reaching out to us from the distant past (ʻou means “reach out for” and mua means “first, in advance of”).

‘Oumuamua appears to be a dark red, elongated metallic or rocky object, measuring about 400 meters long. It is unlike anything normally found in the Solar System.

Currently, ‘Oumuamua is speeding away from the Earth and Sun and fading from view. Following its discovery, astronomers scrambled to acquire as many observations as possible in a short amount of time. Fortunately, the IfA team was already prepared to rapidly follow up solar system discoveries using the Pan-STARRS telescope, which is operated by IfA and funded by NASA.

“We were able to rapidly develop a follow-up strategy on a very short timescale,” said Meech. “It is exciting to think that the brief visit by ʻOumuamua gave us the opportunity to do the first characterization of a sample from another solar system.

As a result, the team is the first to publish their results—“A brief visit from a red and extremely elongated interstellar asteroid”—appearing in the online issue of the journal Nature on Nov. 20, 2017.