spaceSpace and Physics

Asteroid Coming From Another Star Could Be One Of Thousands


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockNov 17 2017, 16:01 UTC

An image of A/2017 U1. Queens University Belfast

A few weeks ago, researchers announced the discovery of an asteroid coming from beyond the Solar System. More observations of the object, known as A/2017 U1, were taken and researchers have now disclosed what they have learned so far.

The new information is available on arXiv and has been submitted for publication in the Astrophysical Journal Letters.


The most remarkable find is just how unremarkable this object is. It looks similar to other asteroids in our own Solar System. The object is around 200 meters by 30 meters (650 feet by 100 feet) and only emits a tiny bit of material, suggesting the object is indeed rocky.

“That’s one of the questions we’re trying to answer,” co-author Ralf Kotulla, from the University of Wisconsin-Madison, said in a statement. “Comet or asteroid?”

The team confirmed that the object’s orbit is very high compared to the plane of the Solar System, where most planets are, and that it moves at around 20 kilometers per second (over 40,000 miles per hour) – too high to be caused by perturbations within the Solar System. These observations strengthen the claim that A/2017 U1 is a visitor from another star.

This animation shows the path of A/2017 U1. NASA/JPL-Caltech

“It’s a really rare object. This object has considerable speed. It is not bound to the Sun," added Kotulla. "Its orbit doesn’t take it anywhere near the major planets.”

Both the elongated shape of the object and its color reminded astronomers of some of the Trojan asteroids, a large family of objects that follow and precede Jupiter in its orbit around the Sun. The team point out how it differs from the more remote objects in the Solar System, as these objects tend to be redder.

The team also point out that the asteroid was only spotted because it came so close to Earth. This allowed them to uncover some interesting statistics. It could be possible to find other objects like U1, at a rate of between one per year to one every two years. And given the large volume of space in the Solar System, there could be a lot more of these objects than we expect. The team estimate that there are around 10,000 of them within the orbit of Neptune, about 10 times more than previous estimates (before the detection) suggested.  

Images of an interloper from beyond the Solar System. Wiyn Observatory/Ralf Kotulla

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