Planets bigger than earth may exist ‘at edge of space’

PLANETS as large, or bigger, than the Earth are waiting to be discovered at the edge of the solar system, scientists believe.

Some of them may contain warm oceans in their interiors, opening up the possibility of hidden havens for life trillions of miles from the sun.

The objects are thought to exist in the Oort Cloud, a vast region swarming with comets that marks the outer boundary of the solar system.

The Oort Cloud extends to almost a quarter of the distance between the sun and its nearest neighbouring star, Proxima Centauri.

It is believed to contain as many as a trillion comets, and perhaps 1,000 small planetary bodies.

But computer models and astronomical evidence suggest there may be much bigger objects lurking in the Oort Cloud, some the size of the Earth and Mars, or larger.

Because so little sunlight penetrates the region they inhabit, they would be invisible to ordinary telescopes.

Only highly sensitive instruments capable of detecting the faintest infrared signals would stand a chance of finding them.

Dr Alan Stern, an expert in the outer Solar System from the American space agency Nasa, said: “The problem is it’s like looking for needles in a haystack.

“We have to search very, very hard and very thoroughly for very faint signals.

“A reasonable analogy might be that we have just begun the exploration of North America and we are on the eastern seaboard, and our view doesn’t extend beyond the first 100 kilometres. We’re preparing to explore all the way westward, and we don’t know what we’ll find.”

There was “forensic evidence” pointing to the existence of large undiscovered planets, he told the annual meeting of the American Association for the Advancement of Science in Boston.

One clue was the fact that the planet Uranus, an object 20 times the mass of the Earth, was lying on its side. Scientists had worked out that some time in its history Uranus must have been struck by an object three to five times more massive than the Earth.

The Oort Cloud planets are thought to have formed in a zone between the terrestrial planets, such as the Earth and Mars, and the gas giants which include Jupiter and Saturn. They were then swept up by the powerful gravity of the gas giants and thrown out to the edge of the solar system.