Scientists have found an alien asteroid that is sharing Jupiter's orbit, but travelling in the opposite direction around the sun.
The minor planet, which was sucked into our solar system 4.5 billion years ago, measures around two miles across.
Known as 2015 BZ509, it has been in a backward orbit ever since, scientists writing in the Royal Astronomical Society journal said.
Recently, asteroids have been spotted relatively frequently.
A "surprise" asteroid that NASA detected on Christmas Day missed Earth by only 140,000 miles (224,000km), travelling at approximately 21,000mph (34,000kph).
Last November, scientists revealed that a lost interstellar asteroid had entered the solar system after wandering between the stars for hundreds of millions of years.
The dark red, cigar-shaped object, named Oumuamua, is about 400 metres (1,312 ft) long, scientists reported in the journal Nature.
And in October, an asteroid the size of a large house passed by Earth at a distance of about 27,000 miles (44,000km).
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There are said to be millions of asteroids in our solar system, the large majority of which are between the orbits of Mars and Jupiter.
While their size can very widely, the largest is said to be about 1,000km (625 miles) across.
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