Genesis (spacecraft) - Objective

Objective

The mission’s primary science objectives, as paraphrased from the original proposal fact sheet, were:

• To obtain precise solar isotopic abundances of ions in the solar wind, as essentially no data having a precision sufficient for solving planetary science problems are available;
• To obtain greatly improved solar elemental abundances by factor of 3-10 in accuracy over what is in the literature;
• To provide a reservoir of solar matter for 21st century science to be archived similarly as the lunar samples.

Note that the mission's science objectives refer to the composition of the sun, not that of the solar wind. Scientists desire a sample of the sun because evidence suggests that the outer layer of the sun preserves the composition of our early solar nebula. Therefore, knowing the elemental and isotopic composition of the outer layer of our sun is effectively the same as knowing the elemental and isotopic composition of our nebula. We could then use that data to model how planets and other solar-system objects formed and then extend those results to understanding stellar evolution and the formation of solar systems elsewhere in the universe.

Clearly the ideal scientific option would be to send a spacecraft to the sun and grab some solar plasma; however, obtaining solar matter is not that straightforward because of the intense heat (millions of degrees) of the Sun’s superheated gases as well as the dynamic electromagnetic environment of the corona, whose flares regularly interfere with the electronics of distant spacecraft. Luckily, the sun continuously sheds some of its outer layer in the form of solar wind. Even more fortunately, data collected prior to the Genesis mission suggests that the rock-forming elements are thought to maintain their relative proportions throughout the process of solar wind formation.

Accordingly, in order to meet the mission science objectives, the Genesis spacecraft was designed to collect solar wind ions and return them to Earth for analysis. Genesis carried several different solar-wind collectors, all of which passively collected solar wind; that is, the collectors sat in space facing the sun, while the ions in the solar-wind crashed into them at speeds over 200 km/s and, on impact, buried themselves in the surface of the collectors. This passive collection is a process similar to that used by the semi-conductor industry to make certain types of devices, and a simulation of the process is given by the free-access program SRIM.

Most of the Genesis collectors continuously sampled all of the solar wind which the spacecraft encountered (the ‘bulk solar wind’). However, the spacecraft also carried three arrays of collectors which were deployed when specific “regimes” (fast, slow, coronal mass ejections) of solar wind were encountered, as determined by the electron- and ion- monitors on board. These deployable collector arrays were designed to provide data to test the hypothesis that the rock-forming elements keep their relative proportions throughout the processes forming solar wind.

There was a third, important type of collector on Genesis: the concentrator, which collected bulk solar wind, but was discriminating in that it electrostatically repelled hydrogen and had enough voltage that it focused the light solar wind elements (e.g., C, O, N, S) onto a small target, concentrating those ions by a factor of ~20. This concentrator was the electrostatic equivalent of using a parabolic mirror from a telescope to cook a hot dog, and somewhat like using a magnifying glass to start a fire. The objective of the concentrator was to bring back a sample with enhanced amounts of solar wind ions to make it possible for analysts to precisely measure the isotopes of the light elements.