New observations of the Solar System’s first known interstellar asteroid, A/2017 U1, has revealed new and unusual information regarding our visitor from afar, including its size, color — and that it is shaped like a cigar.
Using the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile, astronomers have found that the asteroid, now named ‘Oumuamua, is a dark red color, much like other Kuiper belt objects that orbit on the extreme fringes of the solar system.
‘Oumuamua’s visual magnitude changes by a factor of ten every time it rotates, implying that it has an extremely elongated shape, with a length that is a minimum of five times its diameter, and probably closer to ten times, making it a 400-meter (1,300-foot) cigar-shaped object with a diameter of only 40 meters (130 feet). This shape is completely unheard of amongst all of the known asteroids in our system, and as ‘Oumuamua is rocketing away from the Sun at 137,900 km/h (85,700 mph), astronomers have only a small window to complete their observations.
"This unusually large variation in brightness means that the object is highly elongated: about 10 times as long as it is wide, with a complex, convoluted shape," explains astronomer Karen Meech, of the Institute for Astronomy in Hawaii. "We also found that it has a dark red color, similar to objects in the outer solar system, and confirmed that it is completely inert, without the faintest hint of dust around it." ‘Oumuamua was originally assumed to be a comet, due to its extremely elliptical orbit, but it was quickly found to lack a cometary coma, indicating that it was an asteroid.
"’Oumuamua" is a Hawaiian word meaning "scout", referring to the object’s status of being the first known natural object that has made such a long journey through the cosmos to meet us. The asteroid’s last encounter is estimated to have been 1.3 million years ago with the nearby star system of TYC4742-1027-1, when it would have come close to a half-light year of that system’s star. ‘Oumuamua’s high speed at the time, 103 km/s (64 miles/s), means that it did not originate from that system, but that that was simply one encounter in a much longer journey through the stars.