An international team of astronomers, including two from Hertfordshire, has discovered the youngest planet outside the solar system.

The planet, named BD+20 1790b, is only 35 million years old, making it approximately three times younger than the next youngest planet, at 100 million years old.

It is also six-times the mass of Jupiter - which is about 4.5 billion years old.

Discoverers Dr John Barnes and Dr Maria Cruz Gálvez-Ortiz, from the University of Hertfordshire, along with others from Spain and the USA, have been working together for the past five years.

The planet orbits a young star, at a distance closer than Mercury's orbit of our Sun, taking around eight days to complete the trip.

Astronomers usually ignore young stars when searching for planets, because their intense magnetic field makes it very difficult to pick up the signals of planets.

Older stars, with ages in excess of a billion years, are usually targeted. This means there is a lack of knowledge about early life of a planet, and its evolution.

Dr Gálvez-Ortiz said the planet was detected by using an array of large telescopes, looking for the effect of the planet's gravity as it orbits its star, known as the “Doppler-wobble technique”.

The discovery has just been published in the Astronomy & Astrophysics journal.