The Genesis mission was launched in August 2001 and returned to Earth in September 2004. The spacecraft was sent to a special orbit 1 million km from Earth where it was well away from any contamination and exposed ultra-pure collectors of silicon, diamond and germanium to the solar wind. The aim of the mission was to return solar wind atoms for analysis by instruments on Earth so that the elemental and isotopic abundances of atoms in the solar wind, and by extension the sun, could be determined. The sun contains nearly all the matter in the solar system and is little changed since its formation. Precise analysis of the solar wind therefore gives us the starting composition for material from which the rest of the solar system has been constructed. Knowing the starting composition allows scientists to understand how the material we see in the solar system has evolved and developed over the lifetime of the solar system. The mission also exposed different collectors during different solar wind regimes (slow, fast or coronal mass ejection) so that the present day sun could be studied too.
Although the mission was a success with solar wind atoms implanted into the collectors, the return to Earth was ‘non-optimal’ with the parachutes failing to open.
The collectors were shattered into tens of thousands of pieces and contaminated by Utah desert mud and water – but the pieces were at least back on Earth! Much of the time since the crash landing has been spent learning how to clean the pieces without destroying the implanted solar wind atoms.
We are using the RELAX and instruments to measure the abundances and isotopic compositions of Xe, Kr, Mg, Fe, Al, Na and trace elements implanted into the ultra-pure collectors.
The xenon isotopic composition matches solar wind implanted into illmenite from the moon. Knowledge of the solar xenon isotopic composition allows us to improve models of how and when the Earth’s atmosphere formed. Further work with new samples is now underway.
The Time-of-Flight Secondary Ion Mass Spectrometer is used to depth profile through the outer layers of the collectors and detect the solar wind implanted atoms.
The characteristic lower abundances of these elements at the surface (left hand side of the graph), rising to a peak and then falling again is the expected profile for implanted solar wind. Al abundance is only just above background and we are working at present to reduce background contaminating signals to improve our range of analysed elements.
The values obtained for the isotopic abundances of solar wind Mg are δ25Mg = +7±43‰, δ26Mg = -19±39‰. Although these have quite large error bars due to the low abundance of implanted solar wind, they may be compared to in-situ measurements obtained from the Ulysses and SOHO spacecraft which have error bars typically twice as large as these. We will be reducing the uncertainty on these isotopic ratios in the near future and studying the Mg isotopic composition from different solar wind regimes.
Further information can be found at the Genesis Mission website and details of our team can be found here.