Astronomers using Chile-based Very Large Telescope have estimated that the first-ever object to visit the Solar System from outside is a dark-reddish rock 40 metres wide and 400 metres long. Earlier considered a comet, it was reclassified as an asteroid and named 'Oumuamua. After slingshotting past the Sun at 3,14,280 kmph, 'Oumuamua is heading back into interstellar space, said astronomers.