An asteroid big enough to wipe out a city will pass harmlessly between Earth and the moon’s orbit this weekend, missing both, while providing scientists a chance to study the object close up. Asteroid flybys are common but Nasa said it was rare for one so big to come so close and that events like this occurred only about once a decade. Scientists estimate its size to be somewhere between 40 and 90 metres in diameter. Discovered a month ago, the asteroid known as 2023 DZ2 will pass within 515,000km of the moon on Saturday US time and, several hours later, fly past the Earth at about 28,000km/h. The close encounter will provide astronomers the chance to study a space rock from just over 68,000km away. At less than half the distance from here to the moon, the asteroid will be visible through binoculars and small telescopes. “There is no chance of this ‘city killer’ striking Earth, but its close approach offers a great opportunity for observations,” the European Space Agency’s planetary defence chief, Richard Moissl, said in a statement. Astronomers with the International Asteroid Warning Network see it as good practice for planetary defence if and when a dangerous asteroid is discovered that could hit Earth, according to Nasa. The Virtual Telescope Project will provide a live webcast of the close approach. The asteroid won’t be back our way again until 2026. Initially there seemed to be a slight chance it might strike Earth when it returned, but scientists have since ruled that out.