Scientists from Britain and Spain believe there could be at least two planets the size of Earth hiding at the edge of the Solar System.

They've observed small, icy objects that orbit the Sun beyond Neptune and Pluto with orbits consistent with objects being influenced by the gravitational pull of planets.

"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," said Carlos de la Fuente Marcos, an astrophysicist at Complutense University of Madrid.

The researchers also looked at the orbit of the dwarf planet 2012 VP113, which is the farthest known object to orbit the sun. It is roughly twice as far from the sun as Pluto. They believe its orbit could also be influenced by a "dark and icy super-Earth" that could be 10 times the size of Earth.

The research is published in the journal Monthly Notices of the Royal Astronomical Society Letters.