In a new study, scientists have explained how a planet-sized version of an electric toaster heats up some exoplanets to puff up to gigantic size.

More than 150 planets have been found orbiting closer to their host stars than Mercury is to the sun.

Many of these star-hugging gas giants - known as "hot Jupiters" because they can have surface temperatures of 2000 degree Celsius or more - have a similar mass to Jupiter but can have up to six times the volume.

Something must be heating the interior of these planets to make them puff up in this way, but scientists have been puzzled regarding it.

The ever-changing gravitational tug of the host star on the orbiting planet would create friction by flexing its interior, possibly generating enough heat to cause the expansion we see.

But this mechanism can't explain how some planets with a circular orbit - such as TrES-4, which is less massive than Jupiter but 1.8 times as wide - get to be so large.

According to a report in New Scientist, Konstantin Batygin and David Stevenson of the California Institute of Technology in Pasadena now suggest that the missing energy could originate in a wind of charged particles circling the planet.

The temperature in the atmospheres of hot Jupiters is high enough to knock large numbers of electrons off atoms like sodium and potassium.

These electrons could then be whipped around by the planet's winds and interact with its magnetic field, generating a current that can extend deep into the planet, heating up its interior like the element of an electric toaster.

Electrons whipped around by winds interact with the planet's magnetic field, generating a current.

"The little power that you're depositing there may be enough to inflate the planet," said Adam Burrows of Princeton University, who models the properties of exoplanets but was not associated with the study.

Burrows added that more detailed modelling is needed to determine whether currents generated this way reach far enough into the interiors of hot Jupiters to puff them up.

"It might only work at some times in some planets," he said.

If the theory proves correct, it could "kill two birds with one stone", said Burrows, because a similar mechanism could play a part in maintaining the speed of wind bands that whip around upiter and Saturn. (ANI)