Meet asteroid 2002 AA29: or Earth's 'little brother'

Astronomers have identified Earth's "little brother" – an asteroid the size of a football pitch that follows an almost identical orbit around the Sun.

Asteroid 2002 AA29, a 100-metre-wide lump of space rock, was discovered by a team of astronomers led by Martin Connors of the Centre for Science at Athabasca University in Canada. Some experts believe it may one day be mined for its minerals.

In a research paper published in the journal Meteoritics and Planetary Science, the scientists calculate that the asteroid does not pose a direct threat to Earth for at least the next several thousand years. Then, its orbit may change enough to cross that of our own planet.

Its shortest distance to Earth will remain more than 4.5 million kilometres (2.8 million miles) – about 12 times the distance between the Moon and the Earth – for the foreseeable future, they say.

Duncan Steele, an expert on asteroids at Salford University, said the asteroid's orbit is similar to the circular path that Earth follows once each year around the Sun.

"It seems to have been trapped in this particular orbit and it oscillates back and forth in relation to the orbit of the Earth. It gets ahead of us and then gets behind, it's called resonance," Dr Steele said.

"There are many oddities like this in the solar system, such as the so-called Trojan satellites which are in the same orbit as Jupiter. We've been searching for Trojans of Earth for many, many years," he said.

The astronomers discovered asteroid 2002 AA29 earlier this year when it made its closest approach to Earth. It is the "first true co-orbital object of Earth" according to the team.

Dr Steele said that if the asteroid were composed of iron and nickel it could prove invaluable for future space missions, who could use the mineral deposits. "In order to exploit space you need raw materials up there," he said.