1I/2017 U1 ‘Oumuamua, the first asteroid of extrasolar origin identified in our Solar System, has had a violent past which is causing it to tumble around chaotically, according to an international team of astronomers led by Queen’s University Belfast.
This artist’s impression shows the first interstellar asteroid — 1I/2017 U1 ‘Oumuamua. Image credit: M. Kornmesser / ESO.
In October 2017, the Pan-STARRS 1 telescope in Hawai’i picked up a faint point of light moving across the sky. It initially looked like a typical small asteroid, but additional observations over the next couple of days allowed its orbit to be computed fairly accurately.
The orbit calculations revealed beyond any doubt that this body did not originate from inside our Solar System, like all other asteroids or comets ever observed, but instead had come from interstellar space.
Although originally classified as a comet, additional observations revealed no signs of cometary activity after it passed closest to the Sun in September 2017. ‘Oumuamua was reclassified as an interstellar asteroid.
Since October, Queen’s University Belfast researcher Wesley Fraser and co-authors have been analyzing the brightness measurements of the object.
The astronomers discovered that ‘Oumuamua wasn’t spinning periodically like most of the small asteroids and bodies that we see in our Solar System.
Instead, it is tumbling, or spinning chaotically, and could have been for many billions of years.
While it is difficult to pinpoint the exact reason for this, it is thought that ‘Oumuamua impacted with another asteroid before it was fiercely thrown out of its system and into interstellar space.
“Our modeling of this body suggests the tumbling will last for many billions of years to hundreds of billions of years before internal stresses cause it to rotate normally again,” Dr. Fraser said.
“While we don’t know the cause of the tumbling, we predict that it was most likely sent tumbling by an impact with another planetesimal in its system, before it was ejected into interstellar space.”
Until now, astronomers had been puzzled that ‘Oumuamua’s color varied between measurements.
However, the team’s research has now revealed that its surface is spotty and that when the long face of the cucumber-shaped object was facing telescopes on Earth it was largely red but the rest of the body was neutral colored, like dirty snow.
“Most of the surface reflects neutrally but one of its long faces has a large red region,” Dr. Fraser said.
“This argues for broad compositional variations, which is unusual for such a small body.”
“We now know that beyond its unusual elongated shape, this space cucumber had origins around another star, has had a violent past, and tumbles chaotically because of it,” he said.
“Our results are really helping to paint a more complete picture of this strange interstellar interloper.”
“It is quite unusual compared to most asteroids and comets we see in our own Solar System.”
The findings are published in the journal Nature Astronomy.
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Wesley C. Fraser et al. The tumbling rotational state of 1I/‘Oumuamua. Nature Astronomy, published online February 9, 2018; doi: 10.1038/s41550-018-0398-z
