The Moon’s long-lost sister may have been discovered – hiding 34 million miles away behind Mars.

After analysis, astronomers say the asteroid – around 1,000 yards across – appears to be made of the same material as our own Moon.

The asteroid occupies a so-called Lagrange Point near Mars, where the gravitational pulls of the planet and the Sun are in perfect balance.

The current best theory about the Moon’s formation is that around 4.5 billion years ago a planet roughly the size of Mars slammed into the Earth. The ancient planet, called Theia, was completely destroyed in the titanic collision and some of the debris later came together to form the Moon.

The object, an asteroid about a kilometre wide, was first spotted 22 years ago

The asteroid known as (101429) 1998 VF31 appears to have been created in the same collision – or at least soon afterwards.

Spectrographic analysis reveals that the mysterious body is made of the same material as the Moon.

"In a nutshell, it has the same colour as the moon," Apostolos Christou, an astronomer at the Armagh Observatory and Planetarium, told The Times.

"We looked at how it reflects light from the sun and what's interesting is that the colour is more similar to the colour of the moon than the colour of all other asteroids. Among asteroids, it's unique.”

Phobos is in a slowly decaying orbit and is expected to one day collide with Mars

A second possibility explaining the unique asteroid’s origin is that it was formed by an object colliding with Mars.

In the early days of the Solar System, the space around the Sun was a veritable pinball table of colliding objects.

Dr Christou explains: "Large asteroids — we call these planetesimals — were hitting the moon and the other planets.

“A shard from such a collision could have reached the orbit of Mars when the planet was still forming and was trapped in its Trojan clouds."

The asteroid is a trojan – sharing an orbit with Mars

Mars has two moons – Phobos and Deimos – which have long baffled astronomers.

Their small size and unusual shape suggests that they are asteroids that were "captured" by the Red Planet's gravity billions of years ago, but their orbits are inconsistent with that origin story.

Even more mysteriously Phobos has a "monolith" on its surface that sticks up like a skyscraper from the tiny moon. A future NASA probe is planned to land near the monolith and investigate its geology.

Theia, which is estimated to have been around 3,800 miles in diameter, not only helped create our Moon when it smashed into the Earth – it is also thought to have delivered much of our planet’s water and contributed to Earth’s unusually massive core – protecting early life from solar radiation.