|
''Genesis'' was a NASA sample return probe that collected a sample of solar wind and returned it to Earth for analysis. It was the first NASA sample return mission to return material since the Apollo Program, and the first to return material from beyond the orbit of the Moon.〔The NASA ''Stardust'' mission launched two years before ''Genesis'', but did not return to Earth until two years after Genesis's return.〕 ''Genesis'' was launched on August 8, 2001, and crash-landed in Utah on September 8, 2004, after a design flaw prevented the deployment of its drogue parachute. The crash contaminated many of the sample collectors, and although most were damaged, many of the collectors were successfully recovered.〔(【引用サイトリンク】publisher=NASA )〕 The ''Genesis'' science team demonstrated that some of the contamination could be removed or avoided, and that the solar wind could be analyzed using a variety of approaches.〔(【引用サイトリンク】publisher=NASA )〕 It is relatively easy to detect the solar wind, but the precision measurements are difficult and techniques are still being refined in laboratories worldwide. Nonetheless, in March 2008 scientists stated that they believed that all of the mission's major science objectives would be achieved successfully. ==Objectives== The mission’s primary science objectives, as paraphrased from the original proposal fact sheet, were:〔(【引用サイトリンク】publisher=NASA JPL )〕 : * 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 the 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 itself and collect some solar plasma; however, obtaining solar matter is difficult because of the intense heat of the Sun’s superheated gases, as well as the dynamic electromagnetic environment of the solar corona, whose flares regularly interfere with the electronics of distant spacecraft. Fortunately, the Sun continuously sheds some of its outer layer in the form of solar wind, and 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.〔(【引用サイトリンク】first=James F )〕 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 which form the solar wind. There was a third 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 to focus the lighter solar wind elements onto a small target, concentrating those ions by a factor of ~20. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Genesis (spacecraft)」の詳細全文を読む スポンサード リンク
|