In a first, NASA scientists have discovered an “interstellar object” – a small asteroid or comet that appears to have originated from outside the solar system, coming from somewhere else in our galaxy. The object – designated A/2017 U1 – is less than a 400 metres in diameter and is moving remarkably fast. Astronomers are urgently working to point telescopes around the world and in space at this notable object. Once these data are obtained and analysed, astronomers may know more about the origin and possibly composition of the object. A/2017 U1 was discovered by the University of Hawaii’s Pan-STARRS 1 telescope during the course of its nightly search for near-Earth objects for NASA. Rob Weryk, a postdoctoral researcher at the University of Hawaii Institute for Astronomy (IfA), was first to identify the moving object and submit it to the Minor Planet Center. “Its motion could not be explained using either a normal solar system asteroid or comet orbit,” Weryk said. “This is the most extreme orbit I have ever seen,” said Davide Farnocchia, a scientist at NASA’s Center for Near-Earth Object Studies (CNEOS) at the agency’s Jet Propulsion Laboratory in the US. “It is going extremely fast and on such a trajectory that we can say with confidence that this object is on its way out of the solar system and not coming back,” said Farnocchia.
The CNEOS team plotted the object’s current trajectory and even looked into its future. A/2017 U1 came from the direction of the constellation Lyra, cruising through interstellar space at a brisk clip of 25.5 kilometres per second. It is most likely of interstellar origin. Approaching from above, it was closest to the Sun on September 9. Travelling at 44 kilometres per second, the comet is headed away from the Earth and Sun on its way out of the solar system. The object approached our solar system from almost directly “above” the ecliptic, the approximate plane in space where the planets and most asteroids orbit the Sun, so it did not have any close encounters with the eight major planets during its plunge toward the Sun.
On September 2, the body crossed under the ecliptic plane just inside of Mercury’s orbit and then made its closest approach to the Sun. Pulled by the Sun’s gravity, the object made a hairpin turn under our solar system, passing under Earth’s orbit on October 14 at a distance of about 24 million kilometres – about 60 times the distance to the Moon. It has now shot back up above the plane of the planets and, travelling at 44 kilometres per second with respect to the Sun, the object is speeding toward the constellation Pegasus.
“We have long suspected that these objects should exist, because during the process of planet formation a lot of material should be ejected from planetary systems,” said Karen Meech, an astronomer at the IfA. Since this is the first object of its type ever discovered, rules for naming this type of object will need to be established by the International Astronomical Union.