Nasa's mission to the edge of the solar system, and beyond

Buzz Lightyear wanted to go to infinity and beyond, now the US National Aeronautics and Space Administration (Nasa) wants to venture almost as far with a survey of the edge of the solar system.

Buzz Lightyear wanted to go to infinity and beyond, now the US National Aeronautics and Space Administration (Nasa) wants to venture almost as far with a survey of the edge of the solar system.

The mission will involve launching a space laboratory and could answer some basic questions about the nature of interstellar space, as well as laying the groundwork for the first journey of exploration beyond our solar system to the stars and their planets.

Nasa has given the go-ahead for the Interstellar Boundary Explorer - or Ibex - to be built. It will be launched in 2008 from a Pegasus rocket, which will be dropped from the underbelly of a high-altitude aircraft.

It will be the first time that a spacecraft will be launched that has the ability to take images of the boundary at the very limits of the solar system, said David McComas, the mission's principal investigator.

"Ibex will make the first images of the interstellar boundaries beyond our solar system, thereby providing a first step to exploring the galactic frontier," Dr McComas said.

"This mission will provide a much deeper understanding of the Sun's interaction with the galaxy and will also address a serious challenge facing manned exploration by studying the region that shields us from the majority of galactic cosmic ray radiation," he added.

Scientists call the edge of the solar system the "termination shock" boundary because of the sudden drop in velocity of the solar wind - a blizzard of subatomic particles that stream out from the Sun - as it slows from supersonic to subsonic speeds. "It's a mission of discovery. It's going to tell us a lot about the interstellar medium," Dr McComas said.

Only the Voyager 1 spacecraft, launched in 1977, and its sister ship Voyager 2 have ventured through or close to this outer boundary. But neither was designed to take the sort of images that could be captured by the atomic detectors on board Ibex.

The solar wind is caused by the outer atmosphere of the Sun evaporating into space. It travels at a million miles per hour, creating a protective envelope around the entire solar system that extends far beyond the most distant planets. Ibex will capture images of the solar system's previously invisible outer boundaries to discover how the solar wind interacts with the galactic medium, said Dr McComas.

"In addition to revealing many of the interstellar boundary's unknown properties, Ibex will explore how the solar wind regulates the radiation from the galaxy. This radiation is a major hazard to human space exploration and may have affected the formation and evolution of life on Earth," he said.

Ibex is expected to cost about £75m, relatively cheap for space exploration. It will be launched in a wide, elliptical orbit to avoid the magnetic field of the Earth, which could interfere with the spacecraft's instruments.