NASA's Genesis probe was the first attempt to collect samples of the solar wind and return them to Earth. The spacecraft was launched on 8 August 2001 and placed 1.5 million km from the Earth, where it collected samples for over two years. On its return to Earth in 2004, the capsule parachute failed and it crash-landed in the Utah desert. Despite this setback, scientists were able to recover and analyse most of the sample.

Mission objective

The Genesis spacecraft as it was deployed in orbit around L1, collecting the solar wind. (Image: JPL / LMA) The solar wind is a flow of charged particles from the Sun into space. While the centre of the Sun has been modified by nuclear reactions, researchers believe that the surface, where the solar wind originates, has preserved the composition of the original solar nebula from which the planets were formed.

It is hoped that the sample will be able to provide information on the beginning of our solar system and supply clues to the evolutionary process that has led to the amazing diversity of environments on planets and moons in our solar system.

Planned route

Genesis was placed into orbit around the first Lagrangian point (L1), a place between Earth and the Sun where the gravity of both bodies is balanced. Once there, Genesis unfolded its collector arrays and began collecting the solar wind. After two years, the sample collectors were re-stowed and the spacecraft returned to Earth.

Structure of the spacecraft

The spacecraft carried sample collection arrays designed to entrap some of the invisible charged particles expelled by the Sun. They were made of materials such as silicon, sapphire, gold and diamond.

An ion is an atom or molecule that has a net electrical charge from gaining or losing electrons. The solar wind is made up of ions of different elements such as hydrogen and helium, as well as some heavier elements. On the Genesis spacecraft, an ion concentrator separated out and focussed oxygen and similar mass ions from the solar wind onto a special collector tile; an ion monitor recorded the speed, density and approximate composition of the solar wind and an electron monitor made similar measurements of electrons present.

The sample

A successful trial run for the mid-air helicopter capture of the Genesis sample. Image: JPL Genesis probably captured between 10 and 20 micrograms (where 1 microgram is a millionth of a gram) of the solar wind, equivalent to the mass of a few grains of salt. The samples have now been stored and catalogued under ultra-pure cleanroom conditions and are available for study by the world scientific community over the next few decades.

The solar wind

The solar corona is the outermost part of the Sun's atmosphere. Coronal holes occur where a region is more tenuous than the surrounding corona and are thought to be the primary source of high-speed streams of charged particles from the Sun.

During the period that Genesis collected matter, the Sun was at a high level of activity and relatively small coronal holes occured at different solar latitudes. This means that satellites near Earth, such as Genesis, encountered coronal hole wind more frequently. This is a bonus for the mission – the Genesis science team is most interested in this wind because it is thought to be the closest in composition to the surface of the Sun.

Return to Earth

The Genesis capsule following its crash landing in the Utah desert. Image: NASA / USAF 388th Range Sqd The matter collected was set for return to Earth in September 2004 in a spectacular helicopter capture. As the return capsule descended towards the ground, specially trained pilots aimed to catch it in mid-air to prevent the delicate samples from being disturbed by the impact of a landing. Unfortunately the parachute failed to open, the result of a wrongly oriented sensor and the capsule crashed into the desert at more than 300 km per hour.

Fortunately the capsule hit relatively soft ground and although the collecting wafers were shattered, the remaining large pieces could still be analysed. No water seems to have contaminated the sample and scientists were later able to remove or compensate for the relatively dry dust.

In March 2005 the Genesis team announced the identification of solar wind ions in one of the wafer fragments. As a result they are upbeat about the analysis they can carry out over the next few years – a better outcome than anyone expected.