If their theory proves true, it could 'revolutionise' solar system models

can be explained by presence of dwarf planets

Astronomers believe there are at least two unknown planets waiting to be discovered well beyond Pluto.

They claim these planets are changing the position of objects away from Neptune, causing them to behave in strange ways.

If their theory proves true, scientists say it could 'revolutionise' solar system models.

Scientists say at least two planets could exist in our solar system beyond Pluto (artist's impression pictured)

Astronomers have spent decades debating whether hidden Plutonian planet remains to be discovered within the solar system.

Scientists at the Complutense University of Madrid and the University of Cambridge say there must be at least two planets to explain the orbital behaviour of extreme trans-Neptunian objects.

These objects, known as ETNOs, describe minor worlds such as Pluto that orbit the sun at a greater average distance than Neptune.

The most accepted theory says that the orbits of these objects, which travel beyond Neptune, should be distributed randomly.

They should also fulfil a series of characteristics such as have an inclination of almost 0° and an or angle of perihelion – which is their closest point of the orbit to our sun - close to 0° or 180°.

Last year two researchers from the US discovered a dwarf planet called 2012 VP113 in the Oort cloud, just beyond our solar system. Each one of these images was taken about two hours apart

A trans-Neptunian object is any minor planet in the solar system that orbits the sun at a greater distance on average than Neptune. The largest known trans-Neptunian objects are Pluto and Eris. These are followed by Makemake and Haumea

Yet what is observed in a dozen of these bodies is quite different: the average inclination of their orbit is around 20° and angle of perihelion –31°.

'This excess of objects with unexpected orbital parameters makes us believe that some invisible forces are altering the distribution of the orbital elements of the ETNO,' said Carlos de la Fuente Marcos, a scientist at the UCM and co-author of the study.

WHAT ARE TRANS-NEPTUNIAN OBJECTS? A trans-Neptunian object is any minor planet in the solar system that orbits the sun at a greater distance on average than Neptune. Pluto was the first trans-Neptunian object to be discovered in 1930. Then, more than 60 years later, astronomers found a second trans-Neptunian object, (15760) 1992 QB1. Since then however, over 1,000 trans-Neptunian objects have been discovered. The largest known trans-Neptunian objects are Pluto and Eris. These are followed by Makemake and Haumea. Advertisement

'We consider that the most probable explanation is that other unknown planets exist beyond Neptune and Pluto.'

'The exact number is uncertain, given that the data that we have is limited, but our calculations suggest that there are at least two planets, and probably more, within the confines of our solar system,' adds the astrophysicist.

Their theory goes against the predictions of current models on the formation of the solar system, which state that there are no other planets moving in circular orbits beyond Neptune.

But, the recent discovery by the Alma radio telescope of a planet-forming disk more than 100 astronomical units from the star HL Tauri, suggests that planets can form several hundred astronomical units away from the centre of the system.

Last year two researchers from the US discovered a dwarf planet called 2012 VP113 in the Oort cloud, just beyond our solar system.

They believe that its orbit is influenced by the possible presence of a dark and icy super-Earth, up to ten times larger than our planet.