Astronomers have detected an asteroid not far from Earth, moving in the same orbit around the Sun. The 200-300m-wide rock sits in front of our planet at a gravitational “sweet spot”, and poses no danger. Its position in the sky makes it a so-called Trojan asteroid – a type previously detected only at Jupiter, Neptune and Mars. 2010 TK7, as it is known, was found by Nasa's Wise telescope. The discovery is reported in this week's Nature Journal.