Scientists have mapped the temperatures at different layers of a fiery exoplanet's atmosphere and traced the amount and distribution of water vapour using Nasa's Hubble Space Telescope (HST).

Studying the glow from the turbulent planet WASP-43b, located 260 light-years away, using spectroscopy and by observing its rotation, they have been able to show exactly where and how much of water is present in its atmosphere.

They found the same amount of water as was expected for an object with the same chemical composition as our sun, throwing light on the planet's formation.

The observations show the exoplanet is a place of extremes, where winds move at the speed of sound and the day is as hot as 3,000°F (1,649°C) and night temperatures below 1,000°F (538°C).

The planet which is very close to its orange dwarf star is so hot that all the water in its atmosphere is vaporised, says a Nasa release.

The steam planet

"Water is thought to play an important role in the formation of giant planets, since comet-like bodies bombard young planets, delivering most of the water and other molecules that we can observe," said Jonathan Fortney, a member of the team from the University of California, Santa Cruz.

Being a hot ball of predominantly hydrogen gas, there are no surface features on the planet, such as oceans or continents to track its rotation. What can be measured is the severe temperature difference between the day and night sides.

"These measurements have opened the door for new kinds of ways to compare the properties of different types of planets," said team leader Jacob Bean of the University of Chicago.

The planet is the same size as Jupiter – 11 times the size of Earth – but is nearly twice as dense. The planet being close to its star completes an orbit in just 19 hours.

The team next aims to make water-abundance measurements for different planets.

The results have been presented in two papers, one published online in Science Express and the other in The Astrophysical Journal Letters.