The First-Known Interstellar Asteroid is Like a Giant Tumbling Torpedo

Artist’s impression of the 400-meter-long interstellar asteroid 1I/2017 U1 `Oumuamua. Credit: ESO/M. Kornmesser.

Remember that comet-no-wait-asteroid astronomers discovered in October on a high-velocity hyperbolic orbit around the Sun? It has been determined that the object must be of interstellar origin and, based on follow-up observations over the past several weeks, it’s shaped like nothing that’s ever been seen before.

First designated C/2017 U1 PanSTARRS (due to its discovery with the Pan-STARRS 1 telescope in Hawaii) the object’s name was shortly afterward changed to A/2017 U1 and now it’s been given the designation 1I/2017 U1 `Oumuamua — “I” indicating an interstellar origin and `Oumuamua being from the Hawaiian words for “first outreach,” in this instance to us from another star system!

Animation of the hyperbolic path of the interstellar asteroid `Oumuamua. It made its closest approach to the Sun on Sept. 19, 2017. (NASA)

`Oumuamua is also the first object to receive an interstellar designation by the IAU.

Spectral and light-curve observations have revealed that `Oumuamua is reddish in color—similar to Kuiper Belt Objects and the trojan asteroids that orbit the Sun along with Jupiter—indicating an ancient surface turned dark through long exposure to UV radiation, a rocky or metallic composition and a long, narrow shape like a torpedo. `Oumuamua is about 50 meters wide and at least 400 meters (1300 feet) long—about the length of our largest container ships (or about 300 feet longer than a modern aircraft carrier.) It rotates once every 7 1/2 hours or so.

Animation of Oumuamua’s motion (ESO/M. Kornmesser)

While astronomers have long suspected that objects like this do and have passed through our Solar System on a cosmically regular basis this was the first time ever one has been observed and identified. According to ESO “`Oumuamua may well have been wandering through the Milky Way, unattached to any star system, for hundreds of millions of years before its chance encounter with the Solar System.”

VLT and Gemini South Telescope observation of ‘Oumuamua (center) surrounded by streaks of background stars. ESO/K. Meech et al.

“U1 is a 100m-scale solid object ejected from orbit around another star,” wrote astronomer David Jewitt. “It could be billions of years older than the Sun.”

It would have been great to be able to have a spacecraft rendezvous with `Oumuamua and study it up close or even collect a sample of its surface…imagine, the first material from an entirely extrasolar origin! Unfortunately that is now impossible as `Oumuamua is rapidly heading away from the Sun in the direction of the constellation Pegasus at a speedy 44 km/second…almost 99,000 mph. But now that astronomers know more about what to look for, they are hopeful that more such visitors will be found…it was just unexpected that the first one ended up passing so close to us – just a “mere” 15 million miles on Oct. 14, 2017.

“Pan-STARRS found it very close to Earth, which was surprising to me,” said SwRI’s Alan Stern. “Close-range flybys of Earth should be much rarer than more distant objects. It might mean that there are a lot more of these.”

Source/read more from ESO here and learn more about `Oumuamua from Astronomy Magazine here.

UPDATE 1-24-18: Although this is the first such interstellar asteroid that has been observed, ‘Oumuamua is certainly not unique—the latest analysis by astronomers estimate there are 10^27 objects like this flying around the Milky Way. That’s mass equal to about two Earths for every star in the galaxy! Read more from the American Astronomical Society here.


  1. It’s an impressive discovery. Interstellar intruder the size of a container ship? Should have been called Rama.


  2. voenixrising says:

    see: RENDEZVOUS WITH RAMA, Arthur C. Clarke, 1973


  3. Ramarama says:

    We should be ready to rendezvous when the next one arrives!!


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