By Helen Briggs BBC News Online science reporter

A new golden age of space exploration is set to begin next month with the launch of the first in a series of missions to explore comets.

On 1 July the American space agency (Nasa) will send up a probe destined to fly past two of the icy bodies.

The Comet Nucleus Tour (Contour) will be followed next January by the launch of a daring European Space Agency (Esa) mission.

Rosetta will chase a speeding comet and then, for the first time ever, try to land on it.

There are two more Nasa comet missions in the pipeline. One of them - Deep Impact - will blast a crater the size of a football field out of a comet to study its core. It is due to take off early next year.

The other - Stardust - is designed to snatch a sample of dust from around a comet. The probe was launched in 1999 and is already on its way.

'Time capsules'

Scientists are interested in comets because they represent the primitive building blocks of the Solar System.

"If you want to study the early history of the Solar System it's no good looking at planets like the Earth and Moon," says Dr John Davies, an astronomer at the Royal Observatory, Edinburgh.

Rosetta really is the jewel in the crown of cometary exploration in the next few years

Dr Andrew Coates, University College London

"Comets are time capsules of what was in the Solar System 4.5 billion years ago."

There are other driving forces behind the new endeavours.

Manoeuvring a spacecraft around a comet and then landing on it represents a leap in technology that has only just become possible.

Space agencies are also looking for destinations other than planets, many of which have already been explored.

Golden age

Dr Andrew Coates, of University College London's Mullard Space Science Laboratory, says the new missions are exciting because they will use several techniques and look at different comets.

"These ranges of missions with different types of techniques are leading on to what's going to be a golden age of comet exploration in the next 10 years or so," he told BBC News Online.

Comets

Balls of ice and dust that did not get incorporated into planets when the Solar System was formed. Analysis could reveal more about the Solar System and perhaps life on Earth

Dr Coates is co-investigator for one of the scientific instruments on Rosetta.

He also worked on Esa's Giotto mission, which flew by Comet Halley in March 1986.

He sees the latest Esa mission as a natural progression.

"Rosetta really is the jewel in the crown of cometary exploration in the next few years," says Dr Coates.

"It's the logical next step after Giotto, which flew past a comet at high speed.

"This really takes the science on one step further."