The first known object to come from outside our Solar System is giving up clues as to where it came from. New research led by Dr Alan Jackson at the Centre for Planetary Sciences at the University of Toronto Scarborough indicate there's a high probability that interstellar asteroid 'Oumuamua (1I/2017 U1) came from a binary star system containing at least one hot, massive star.
First detected on October 19, 2017 by the University of Hawaii's Pan-STARRS 1 telescope on Haleakala and plotted as part of a NASA survey to identify near-Earth objects, 'Oumuamua (Hawaiian for "Scout") was initially thought to be a comet. However, its lack of comet-like activity and later analysis of its orbit and light curve indicated that it was an asteroid that had been flying through interstellar space for hundreds of million of years before briefly passing through our system.
After weeks of intense scrutiny, it was determined that 'Oumumua is a rocky spindle measuring about 230 × 35 × 35 m (800 × 100 × 100 ft) with an average diameter of about 110 m (360 ft) and is rotating in such a manner that it likely had a violent origin. Its trajectory had it traveling in an open-ended hyperbolic arc with an eccentricity of 1.2 and at an extreme angle to the ecliptic as it traveled at a velocity of 26 km/s (59,000 mph, 95,000 km/h). Observations established that it's of natural origin and has been drifting through interstellar space for millions of years as it was bombarded by cosmic rays, reducing its surface to a layer of dense organic compounds.
But the real mystery is, where did it come from? Backtracking its trajectory to the constellation of Lyra indicates that it's been circling the galaxy several times since it was ejected from its home system, with our Solar System being the first it has encountered. Exactly which system it came from may never be determined, but according to Jackson, the most probable one is a binary star system.
The Sun is a single star system, but there are many systems made up of two or more stars orbiting one another about a common focus. Jackson's team examined how efficient a binary star is at ejecting objects and correlated this with the number of binaries in the Galaxy. What they discovered was that objects are more likely to be ejected from binary stars as the mass of each companion yanks any planets or other objects out of their proper orbits – much in the way that Jupiter's gravity dislodges asteroids and comets and sends them hurtling into the inner Solar System.
"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," says Jackson.
In addition, the team determined that at least one of the binary companions is a hot, high-mass star because these have more rocky objects orbiting close in. They also believe that 'Oumuamua was probably erected during a time when planets were forming around the stars. The hope is that continuing analysis of the data gleaned from the interstellar wanderer will give new insight into other systems.
"The same way we use comets to better understand planet formation in our own Solar System, maybe this curious object can tell us more about how planets form in other systems," says Jackson.
The study as published in the Monthly Notices of the Royal Astronomical Society.
Source: Royal Astronomical Society
