Trojan asteroids

Spotted by WISE, 2010 TK7 was confirmed as Earth’s first-known Trojan asteroid in July 2011.

Asteroids are the debris of the Solar System – small chunks of rock that never came together to form larger planets. Today, they mostly orbit in the Asteroid Belt between Mars and Jupiter, though some occasionally fall into the inner Solar System and may become near-Earth objects (NEOs).

But there’s another class of asteroids – the Trojans – that dice with death by sharing Jupiter’s own orbit. They do this by clustering together in swarms that lie 60 degrees ahead of, and 60 degrees behind, the giant planet itself, occupying ‘sweet spots’ called Trojan points, or Lagrange points, where the gravitational pulls of the Sun and Jupiter are balanced.

In fact, the Trojans orbit the centre of mass, or barycentre, of the Jupiter-Sun system (which is well inside the Sun). Jovian Trojans were first spotted in the early-1900s, but in recent years we have found Neptune, Uranus, Mars and even Earth have Trojan asteroids of their own.