UNTIL the 1990s there was no evidence for the existence of planets beyond our solar system. But in recent years techniques for detecting planets orbiting stars many light years away have been discovered, While the light from 'extra solar planets' is drowned out by their parent stars there are two methods of detecting them indirectly, and pupils at a Widnes school have just become the first to try their hand with one of the techniques. ADRIAN SHORT reports.

ONE of the most fascinating topics in astronomy came under the spotlight when a professional scientist delivered a workshop on planets which exist elsewhere in the galaxy.

Dr Chris Leigh, an astronomer at Liverpool John Moores University, was joined by physics teacher Andrea Fesmer, of Saints Peter and Paul City Learning Centre (CLC), in leading a workshop which involved pupils looking at real information from space to find out more about the planets which orbit stars other than our own star, the Sun.

The pupils heard that planets out-side of our Sun and its planets (like the Earth and Mars) are called exoplanets.

Exoplanets were unknown until about 15 years ago and, as of July 2005, 161 planets have now been discovered revolving around stars many light years away from the Sun.

The pupils were shown an artist's impression of what an exoplanet may look like and saw real images from the Hubble

Space Telescope of stars surrounded by disks of materials believed to be a collection of dust, chemicals and boulders - from which planets could form in the future.

Dr Leigh said that our own solar system would have looked like that in the distant past.

The pupils learned that the first exo-planet was discovered in 1995 around a star called 51 Pegasi.

Astronomers noticed that 51 Pegasi was wobbling every three-and-a-half days.

Dr Leigh explained that when two objects are stuck together, or are relatively close together, they move around a common centre of mass which causes a wobble in the bigger object's path.

This can be compared to the wobble of a hammer thrower as he swings the hammer around him in athletics.

They realised that the planet must be very close to its parent star if it was able to orbit in three days - unlike the earth which takes 365 days to orbit the Sun. Even the closest planet to the Sun, Mercury, takes 88 days to orbit.

Dr Leigh said the object was so incredibly close to 51 Pegasi that it would have a surface temperature of 1,200ºC, far too hot for life, as we know it, to exist there.

He said that astronomers cannot detect exoplanets visually, as no planet produces any light of its own and, as they are such a long way away, they become lost against the blinding glare of the star they orbit.

Typically an exoplanet would be 20,000 times fainter than the star it orbits, as it merely reflects a small part of the light from that star.

Another way of detecting an exo-planet, apart from looking at its star's wobble, is to look at how much light it blocks off from its star as it passes in front of it. If there is a planet there, then observers can detect a periodic reduction in the brightness of a star.

The pupils at Sts Peter and Paul CLC used computer programs to analyse images taken with the Liverpool Telescope in the Canary Islands of a possible exoplanet star.

The star they looked at was TrES-1-b which is thought to be orbited by a gas giant planet similar to Jupiter - our Sun's largest planet.

Six out of the 161 known exoplanets have been discovered by measuring the fall in light caused as by the exoplanet passes in front of its Sun.

The rest were detected by wobble - even Jupiter causes our own Sun to wobble by a velocity up to 12.5 metres per second in its year (which takes 12 Earth years).

Nine pictures of the TrES-1 star were taken at 10-15 minute intervals, before being looked at by the pupils.

The pupils then used a computer program, which calculated the changes in brightness of the star.

The time taken for known exoplanets to travel once around their stars has been found to range from an incredibly quick year of 2.5 days to a year of more than 5,000 days.

Hopefully, one day, scientists will be able to capture light directly from a distant exoplanet which would let them pinpoint which chemicals are present, and then we'll know exactly what the exoplanets are made of.