Scientists have discovered a previously undetected element in the atmosphere of a planet almost 500 light years from Earth.

Using a cutting-edge technique on one of the most powerful telescopes in the world, the international research team led by the University of Exeter identified potassium in the atmosphere of the planet XO-2b, located in the Lynx constellation.

This comes at the same time as another research team, led by the University of Florida, has announced finding potassium on another distant planet – HD80606b – 190 light years from Earth.

Both the planets are known as hot-Jupiters, meaning they are similar in size to the gas giant in our solar system but are much hotter because they have a much closer orbit to their sun. Temperatures can reach 1,000C (1,832F) or more.

This extreme heat means potassium, which is locked in a solid state on Earth, should be in a gaseous form within the planet's atmosphere. However, until now no one has been able to detect it, though it has long been theorised to be an important part of hot-Jupiter atmospheres.

Dr David Sing, from the University of Exeter's School of Physics and leader of the research, said: "We've finally found an element we've been long expecting, and hoping to find. It's a large step forward as it supports many theories about hot-Jupiter planets. The detection has been made using a new technique which we will be able to apply on many other planets, leading to a far broader understanding of hot-Jupiters and other kinds of planets as we compare their atmospheres."

The find was made using a method known as narrowband transit spectrophotometry — which involves measuring light that has passed through the upper atmospheres of a planet and using highly sensitive equipment to analyse the data.

Dr Eric Ford, from the University of Florida, said: "The new technique opens the door to comparing the abundances of multiple atoms and molecules in several more planets.

"While both planets in the Florida and Exeter studies have potassium, there are interesting differences in the details that provide information about the structure of the planets' atmospheres."

Both studies were carried out using the Gran Telescopio Canarias, which has a huge mirror more than 10 metres wide located more than 7,000 ft above sea-level on a volcanic peak on the Canary Island of La Palma.

Alongside this is the OSIRIS instrument, which precisely measures light received through the telescope within a small range of colours. This minimises the distorting effects of the Earth's atmosphere and allows detailed readings to be taken.

When a planet becomes backlit as it passes in front of its star, the light that has passed through its atmosphere is measured by OSIRIS. Because atoms and molecules absorb light at different wavelengths, scientists can analyse the light readings and determine which molecules are present – in this case, potassium.

The two groups' findings are available online and have been submitted to the journals Astronomy & Astrophysics and the Monthly Notices of the Royal Astronomical Society.

Dr Sing from the University of Exeter and Knicole Colón from the University of Florida will present their findings at the ExoClimes 2010 conference, which starts at the University of Exeter today and runs until Friday.

Some of the world's leading experts in Earth, Solar System and Exoplanet climatology will be attending the event to discuss recent results in this rapidly moving area of research.

Anyone wanting more information about the event can go to www.exoclimes.org.