A mosaic of four images of the near-Earth asteroid Eros, taken by the NEAR probe on 14 February 2000. Image: NASA / Johns Hopkins University / Applied Physics Laboratory Amateur astronomers in the United States watched on the morning of 3 July as a mountain-sized asteroid raced past the Earth.

The unnamed object, catalogued as 2004 XP14, passed just 430000 km away at 0444 GMT (0544 BST or local time in the UK). This is a little further than the distance from the Earth to the Moon and a small step on the scale of the Solar system.

2004 XP14 is between 400 and 900 m across or about the size of a small mountain. It is classed as a Potentially Hazardous Asteroid (PHA) meaning that it could collide with the Earth at some point in the future. Fortunately, astronomers have ruled this out for at least a century, but this event reinforces the argument for finding and keeping a close watch on the hundreds of PHAs that regularly pass near our home planet.