Interstellar Interloper 1I/’Oumuamua Gone Forever

1IP/’Ououaoua, also known as 1I/2017 U1, was spotted whizzing through the solar system in images taken with the WIYN telescope. The faint streaks are background stars. In these images U1 is about 10 million times fainter than the faintest stars visible with the naked eye. Credit: R. Kotulla (University of Wisconsin) & WIYN/NOAO/AURA/NSF

Back in October, astronomers discovered the first known interstellar object passing through our solar system. Interstellar meaning that it came from another planet around another star and was somehow ejected into space.Here in our neck of the woods that likely happened when Jupiter and Saturn migrated across the solar system some half-billion years after its formation, scattering smaller objects helter-skelter either into outer space or smack into other planets to blast out millions of craters.

The object was originally thought to be a comet but showed no activity like a fuzzy coma or tail (caused by vaporization of ice) and so is now believed to be an asteroid. In a sequence of images taken over 5 nights with the 3.5-meter WIYN telescope at Kitt Peak National Observatory and with the 2.5-m Nordic Optical Telescope on La Palma in the Canary Islands, the object was found to be small, slightly red and varying brightness with an 8 hour period. Both properties are similar to those of asteroids in the inner solar system.

The WIYN telescope and building, shown against the sunset sky, is being used to study the new object in detail to determine its makeup, rotation rate and more. Credit: M. Hanna & NOAO/AURA/NSF

The name, 1I/’Oumuamua, was chosen by the team who discovered it using Hawaii’s Pan-STARRS telescope. The “1” means first and the capital letter “I” stands for interstellar. The name is of Hawaiian origin and reflects the way this object is like a scout or messenger sent from the distant past to reach out to us: ‘Ou means reach out for, and mua means first or in advance of. The second mua emphasizes the meaning of the first.

One thing’s for sure: the object’s hyperbolic orbit ensures we’ll never see it again. A classic one-hit wonder, the asteroid zoomed in, grabbed a couple of popcorn shrimp and zoomed out, never to return.

The tipoff that 1I/’Oumuamua was from outside the solar system was its hyperbolic orbit. Hyperbolas are open ended and don’t circle back like a circle or an ellipse, only in and then out. Credit: NASA/JPL

From the changing brightness observed as it rotated, the team inferred that 1I is really stretched out with rough dimensions of 100 feet x 100 feet x 590 feet (30m x 30m x 180m). About twice the height of the Statue of Liberty, the asteroid is “similar to the proportions of a fire extinguisher — although not as red as that,” says David Jewitt (UCLA), the first author of a study of the unique object. In fact, except for its shape, it’s not particularly remarkable. This neatly confirms what we know already, that the ingredients our solar system works with to produce the wonderful assortment of planets we love, operates elsewhere. That may also include life.

Five separate images of the interstellar asteroid captured by the WIYN telescope. Credit: R. Kotulla (University of Wisconsin) & WIYN/NOAO/AURA/NSF

If planets form around other stars the same way they did in our solar system, many objects the size of 1I are predicted to be ejected in the process. With over 3,700 planets known — and we’ve only just begun — ejected comets and asteroids should be as common in the galaxy as fidget spinners.  The authors of a recently submitted paper on the new object estimate that based on the properties of 1I, there are about 10,000 similar interstellar objects its size closer to the Sun than Neptune at any given time.

“Each one whizzes through the solar system in about 10 years,” says Jewitt, “and every 10 years or so, we have a completely new bunch of these objects, a few of which we can hope to see.”

Future surveys designed to detect moving objects, such as the wide, fast, deep survey to be carried out with the Large Synoptic Survey Telescope are likely to discover more of these one-timers, giving us further opportunities to study the little stuff from beyond the solar system.