Astrophysicists have discovered planets outside our galaxy for the first time ever.

Previously, planets have only been detected within the Milky Way – the galaxy in which Earth is located.

However, by measuring an astronomical phenomenon called microlensing, scientists were able to identify a group of distant worlds using data from Nasa’s Chandra X-ray Observatory.

The newly discovered planets ranged from the size of the moon to the size of Jupiter, and their galaxy is 3.8 billion light years away from our own.

"We are very excited about this discovery. This is the first time anyone has discovered planets outside our galaxy," said Professor Xinyu Dai, an astrophysicist at the University of Oklahoma.

The findings were published by Professor Dai and his colleague Dr Eduardo Guerras in The Astrophysical Journal.

Analysis of microlensing, which makes use of the brightness of distant celestial objects such as stars and quasars, is the only known method capable of identifying planets at such distances.

"This is an example of how powerful the techniques of analysis of extragalactic microlensing can be,” said Dr Guerras.

“This galaxy is located 3.8 billion light years away, and there is not the slightest chance of observing these planets directly, not even with the best telescope one can imagine in a science fiction scenario.