Page last updated at 10:51 GMT, Monday, 20 October 2008 11:51 UK

Probe studies Solar System's edge

Ibex under construction (SWRI)
The Ibex probe will chart particle interactions at the edge of deep space

Nasa's Interstellar Boundary Explorer (Ibex) spacecraft has been launched into Earth orbit to study the edge of our Solar System.

Ibex was launched on Sunday aboard a Pegasus rocket that was dropped from a jet flying over the Pacific Ocean.

It is the first probe to study particle interactions at the boundary where our Solar System meets interstellar space.

The two-year mission should shed light on the decline of the solar wind, which is at its lowest pressure in 50 years.

The interstellar boundary is the point in space at which the particles emitted from the Sun begin to compete with those from elsewhere in the galaxy.

This region serves as a buffer that protects the Solar System's interior from 90% of the cosmic rays heading towards it.


Ibex launches on a Pegasus rocket over the Pacific Ocean

Recent observations have seen a reduction in the solar wind that propels particles towards the boundary. The level has dropped by 25% in the last decade, reaching a 50-year low.

The two Voyager spacecraft, launched in 1977, are currently in the "termination shock" zone, where the particles from the Sun crash into those from interstellar space.

"The Voyager spacecraft are making fascinating observations of the local conditions at two points beyond the termination shock that show totally unexpected results and challenge many of our notions about this important region," said David McComas, the mission's lead scientist, who is based at the Southwest Research Institute in San Antonio, Texas.

The 50cm-wide octagonal spacecraft will use two cameras to take images of the boundary region.

It will study both the outbound solar particles and the incoming cosmic rays, providing more insight into the particle interactions that occur there.

The probe was developed at the Southwest Research Institute and is part of a new generation of small-scale, directed projects in the US space agency's Small Explorers programme.

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