This illustration shows one of the darkest known exoplanets — WASP-12b — orbiting a star like our Sun. NASA/ESA/G. Bacon

Nasa's Hubble Space Telescope has revealed details of a strange planet that looks entirely black –because it traps at least 94% of the visible light that falls onto it.

The exoplanet, called WASP-12b, resides outside our solar system 1,400 light years from Earth. It belongs to a class of planets called 'hot Jupiters' – gaseous giants that orbit in close proximity to their host star and are heated to extreme temperatures.

As a result, most molecules on the day side of the planet – where the temperature is over 2,500 degrees Celsius – are unable to survive. This means that clouds – which reflect light into space – probably cannot form and so any light penetrates deep into the planet, where it is absorbed by hydrogen atoms and converted to energy.

"We did not expect to find such a dark exoplanet," said Taylor Bell from McGill University and lead researcher of the Hubble study. "Most hot Jupiters reflect about 40% of starlight."

"There are other hot Jupiters that have been found to be remarkably black, but they are much cooler than WASP-12b. For those planets, it is suggested that things like clouds and alkali metals are the reason for the absorption of light, but those don't work for WASP-12b because it is so incredibly hot,"

WASP-12b is tidally locked – meaning one side always experiences day while on the other, it's always night. This occurs because it is very close to its parent star, in a region where the effect of gravity is so strong that the planet has been squashed into an egg shape. Meanwhile the temperature differences between the two sides are vast – the night time side is more than 1,000 degrees cooler than the daytime side.

"This new Hubble research further demonstrates the vast diversity among the strange population of hot Jupiters," Bell said. "You can have planets like WASP-12b that are 4,600 degrees Fahrenheit and some that are 2,200 degrees Fahrenheit, and they're both called hot Jupiters."

WASP-12b was first spotted in 2008 and has been studied by a variety of telescopes, but its light-eating abilities are only now becoming clear. To calculate the scale of this phenomenon, astronomers used Hubble to observe the planet as it passed directly behind the star. The amount of dimming detected by the telescope tells astronomers how much reflected light is given off by the planet. But Hubble could not detect any reflected light, meaning the daytime side absorbed everything falling onto it.