1I/2017 U1 ‘Oumuamua, the first asteroid of extrasolar origin identified in the Solar System, likely came from a binary star system, according to new research published in the Monthly Notices of the Royal Astronomical Society.
This artist’s impression shows ‘Oumuamua. Image credit: Joy Pollard / Gemini Observatory / AURA / NSF.
‘Oumuamua was first spotted by University of Hawaii astronomer Robert Weryk using the Pan-STARRS telescope at Haleakala Observatory in October 2017.
Although originally classified as a comet, further observations revealed no signs of cometary activity after it passed closest to the Sun in September 2017. The object was reclassified as an interstellar asteroid and named 1I/2017 U1.
With a length of at least 1,300 feet (400 m), a diameter of 335 feet (100 m), and traveling at a blistering speed of 67,100 mph (30 km per second), at its closest it was about 20.5 million miles (33 million km) from Earth.
Astronomers were fairly sure the object was from outside our Solar System, based on its trajectory and speed. An eccentricity of 1.2 — which classifies its path as an open-ended hyperbolic orbit — and such a high speed meant it was not bound by the gravity of the Sun.
“It’s remarkable that we’ve now seen for the first time a physical object from outside our Solar System,” said study lead author Dr. Alan Jackson, a postdoc at the Centre for Planetary Sciences at the University of Toronto Scarborough in Canada.
For the study, Dr. Jackson and colleagues set about testing how efficient binary star systems are at ejecting objects.
The astronomers also looked at how common these star systems are in our Milky Way Galaxy.
They found that rocky objects like ‘Oumuamua are far more likely to come from binary than single star systems.
They were also able to determine that rocky objects are ejected from binary systems in comparable numbers to icy objects.
“It’s really odd that the first object we would see from outside our system would be an asteroid, because a comet would be a lot easier to spot and the Solar System ejects many more comets than asteroids,” Dr. Jackson said.
Once they determined that binary systems are very efficient at ejecting rocky objects, and that a sufficient number of them exist, the researchers were satisfied that ‘Oumuamua very likely came from a binary system.
They also concluded that it probably came from a system with a relatively hot, high mass star since such a system would have a greater number of rocky objects closer in.
“‘Oumuamua was very likely to have been ejected from its binary system sometime during the formation of planets,” Dr. Jackson and co-authors said.
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Alan P. Jackson et al. Ejection of rocky and icy material from binary star systems: Implications for the origin and composition of 1I/‘Oumuamua. MNRAS, published online March 19, 2018; doi: 10.1093/mnrasl/sly033
