Astronomers find the Moon’s ‘long-lost twin

The long-lost twin of the moon has been spotted trailing behind Mars, according to a new study.

The 3,280-foot-wide asteroid called (101429) 1998 VF31 was first spotted 22 years ago, and new analysis reveals it is ‘strikingly similar’ to the moon.

Scientists from the Armagh Observatory and Planetarium (AOP) in Northern Ireland used the European Southern Observatory’s (ESO) and the Very Large Telescope (VLT) to study the space rock.

The lead author of the study, Dr Apostolos Christou from the AOP, believes it is possibly a chunk of moon that was dislodged by an enormous impact during the Solar System’s formative years, around four billion years ago.

However, while the origin of this rock may be lunar, the research team say it is also possible it could have stemmed from the Martian surface.

The asteroid is a Mars Trojan which orbits the Sun while trailing behind the red planet at an angle of about 60 degrees relative to the Sun, in a so-called Lagrange point. These are locations in a planet’s orbit where the gravity of the Sun and the planet balances out, allowing a rock to remain in a static location.

The asteroid is a Mars Trojan which orbits the Sun while trailing behind the red planet at an angle of about 60 degrees relative to the Sun, in a so-called Lagrange point. These are locations in a planet’s orbit where the gravity of the Sun and the planet balances out, allowing a rock to remain in a static location. L4 is ahead of Mars and L5, where VF31 is, sits behind Mars

Dr Christou studied the space rock with a technique called spectral matching.

‘It’s similar to the photo-IDing done by the police when chasing crooks, you try to match your data – the spectral profile – against the same type of data taken from other objects, for example other asteroids or meteorites,’ he told.

‘None of these matches were particularly satisfactory until we included spectra of the Moon in our analysis. The similarity to parts of the lunar surface was striking.’

The asteroid is part of a group known as Mars Trojans, and their origin is a long-standing astronomical mystery.

They orbit the Sun while either trailing behind the red planet at an angle of about 60 degrees relative to the Sun, L5, or 60° in front of Mars, L4.

For example, if Mars reaches a point in its orbit deemed to be the same as 12 o’clock on a clock face, the Trojans will be at two o’clock.

They stay in this location because they are trapped at a Lagrange Point, a patch of space where the gravitational pull of various celestial bodies balances out.

As a result, they never go around Mars and always lurk behind it, following in the planet’s wake.

The study, which was funded by the UK Science and Technology Facilities Council (STFC), reveals that VF31 is very different in composition to all the other Mars Trojans.

This, Dr Chrisotu told MailOnline, was surprising. None of the other Trojans had any resemblance to the moon, making this object unique.

The research team speculates that the moon may have been struck by an asteroid, called a planetesimal, causing VF31 to chip off the surface.

‘The early solar system was very different from the place we see today,’ Dr Christou says.

‘The space between the newly-formed planets was full of debris and collisions were commonplace.

‘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.’