Dr Robin Catchpole casts doubt on NASA's claims

Dr Robin Catchpole believes a lot more work needs to be done before such conclusions are drawn.

The new object, in the constellation of Taurus, was found by the Hubble space telescope.

Nasa believes it may be a planet two or three times the mass of Jupiter, the largest planet in our solar system.

Alternatively it could be a brown dwarf star, one that was too small to sustain the nuclear reactions in its core that normal stars need to shine.

But although Dr Catchpole admits that the brown dwarf explanation is feasible, he says more work is needed before further conclusions can be drawn.

"I really don't think there's any evidence to say that what we are seeing here is a planet", he told BBC World Service, adding that scientists needed to use another instrument to determine what sort of light the object was giving out.

A spectrum of the object would tell researchers whether it was hot and luminous like a star or cool and reflective like a planet.

"This one looks far too bright to be reflecting the light of the stars nearby," he said

Although he accepted the discovery had potential, he said: "A lot more work has to be done before it's right to go out and tell everybody you've found a planet."

This could be done with the biggest telescope in the world which this week produced its first pictures of space.

The new instrument built by eight European nations in northern Chile would be able to gather the light, analyse it and tell us exactly what it is made of.

Dr Catchpole believes Nasa's release of the story was symptomatic of an increasing tendency for scientists "to grab the headlines as soon as possible."

He said this was driven by the need to get funding for research and searching for life in other worlds was an area where there was a lot of competition.