Pan-STARRS telescope spots interstellar object
The first interstellar object observed in the solar system, first spotted by the Pan-STARRS telescope atop Haleakala in October, has a severe elongated shape to the extent never seen before in space objects, according to a University of Hawaii astronomer.
The object, named ‘Oumuamua, has a “triaxial ellipsoid” shape based on light-curve data and is viewed as an ellipse from any direction, Karen Meech, of the UH Institute of Astronomy, said last week.
“Most small things in the solar system have approximately this shape,” she said in an email. “What is really unusual is how elongated this is.”
In the light-curve database of asteroids, which contains about 20,000 light curves, there are only five indicating the objects are “quite elongated,” she said. Those have a ratio of length to width of 6-to-1 at most, “but there is nothing in our solar system that we have seen with a 10-to-1 axis ratio” like ‘Oumuamua, she said.
Astronomers don’t understand how an object the shape of ‘Oumuamua was created, Meech said. But once that is understood, it may be possible to determine where the object came from, though that question is premature now, she emphasized.
‘Oumuamua was too faint to determine its composition and whether it contains materials unknown to the solar system, Meech said. Its surface reflected red, which means it reflected red light more efficiently than blue light. Many objects have that characteristic, including some organic material, minerals and iron particles, and many objects in the solar system have that trait, such as comets, outer solar system asteroids and iron meteorites.
“So all we can say is it appears similar to things in our solar system, but this does not preclude it being dissimilar,” she said.
‘Oumuamua was more than 167 million miles away from Earth early last week and very difficult to track from the ground, said Meech. Its distance from the Earth is increasing 3.7 million miles a day. Observations of the interstellar object by the Hubble Space Telescope are planned this month.
She said ‘Oumuamua is relatively small and moving very fast through the inner solar system, “where it was bright enough to see.” The object passed under the Earth’s orbit Oct. 14 at a distance of 15 million miles, about 60 times the distance to the moon. It is currently headed out of the solar system.
To find these interstellar objects, astronomers need big telescopes, like Pan-STARRS, doing all-sky surveys and “looking at the right place in the sky at the right time and be able to see faint things,” she said.
Several surveys currently are dedicated to doing that, Meech said. The search will be aided by the Large Synoptic Survey Telescope with an 8-meter diameter telescope being built in Chile. The telescope, expected to be operational in 2022, has a larger mirror to see fainter objects.
“I suspect we will be seeing a lot more of these things,” interstellar objects, in the future, she said. Interstellar objects have been predicted to exist for a long time, but Pan-STARRS was the first to see one.
Rob Weryk, a postdoctoral researcher at UH, noticed the unusual object in images taken by Pan-STARRS on Oct. 19 during the course of its nightly search for near-Earth objects for NASA. The object’s orbit could not be explained as a solar system asteroid or comet.
Originally named A/2017 U1 (with the “A” for asteroid), the object is the first to receive an “I” (for interstellar) designation from the International Astronomical Union, which created the new category after the discovery.
The interstellar object also has been officially named ‘Oumuamua, which was chosen in consultation with UH-Hilo Hawaiian language experts Ka’iu Kimura and Larry Kimura, a UH news release said. The name reflects the way the object is like a scout or messenger sent from the distant past to reach out to humankind. ‘Ou means “reach out for” and mua, with the second mua placing emphasis, means “first, in advance of.”
The object’s full official name is 1I/2017 U1 (‘Oumuamua) and can also be correctly referred to as 1I, 1I/2017 U1 and 1I/’Oumuamua.
“It is exciting to think that the brief visit by ‘Oumuamua gave us the opportunity to do the first characterization of a sample from another solar system,” said Meech.
An international team led by Meech has made detailed measurements of the object’s properties. Her team was the first to publish its results in an article in the Nov. 20 edition of the journal Nature titled, “A brief visit from a red and extremely elongated interstellar asteroid.”
* Lee Imada can be reached at firstname.lastname@example.org.