STUDY OF THE METEORITES: THE IMPLEMENTATION OF G–SEO (GIGA. SCAN. ELECTRON OBSERVATORY)
One of the original projects developed as part of the IEMS research is the implementation of a new method of investigation of meteoritic materials, based on analyses effectuated through G-SEO (Gigantic Scanning Electron Observatory), an innovative instrument which results from the evolution of the traditional SEM (Scanning Electron Microscope).
The SEM figures nowadays among the equipment of many laboratories, both scientific and non-scientific. The research and collection of meteorites draws the attention of an increasingly big number of people from both the academic and the industrial worlds. This growing interest leads to a progress in the study of meteorites and to an improvement in the comprehension of the mechanisms that led to the formation of the Solar System.
When used to distinguish terrestrial rocks from non-terrestrial ones, the SEM is a quick and efficient device. However, the SEM is not able to provide an exact and complete analysis for many reasons listed below. The SEM proves, thus, to be an inappropriate device if one considers the aims of the IEMS mission and the necessity to guarantee the absolute accuracy of the analyses of all the findings. For this reason, the IEMS researchers implementedG-SEO, a very powerful device, equipped with an unparalleled degree of accuracy, both on the microscopic and the macroscopic levels, and infallible even in the face of heterogeneous materials.
METEORITES BELONG TO THREE CATEGORIES
[1] SIDEROLITES (meteorites whose metallic and silicate components are comparable. They constitute circa 1 pct. of the total).
[2] SIDERITI (ferrous meteorites, they constitute circa 8 pct. of the total).
[3] AEROLITES (stony meteorites, the most common). In turn, the aerolites are divided into three subcategories: the ANCODRITES, the SNC of Martial provenience, and the HED, which come from planet Vesta. The condrites are characterized by the presence, inside a silicate core, of small glass spheres (condrules) of millimetric dimensions, composed of Iron and Magnesium silicates produced by the fusion of primordial proto-planetary material. In many cases, grains of even older materials rich in metallic oxides formed at least 2 million years before the condrules are present.
HOW DOES THE SEM WORKS
The founding/fundamental principle of the SEM (Scanning Electron Microscope) is that it can construct an image step by step, thanks to an electron beam which is projected on the sample and scans itby sectioning it into different sections. The SEMs of the latest generation have a power of 10 nm, with zooms that range from 20 to 100000x. The electron beam is produced, as a result of ion-thermal, by a filament of esaborurus of Lanthanium and brought into focus bymagnetic lenses. The electrons are accelerated through a potential difference which varies between 0.3 and 30 KV. Thescansion of the surface is rendered possible by the fact that the electrons are deflected by going through a system of special magnets. For the SEM’s scansions it is necessary to cut a thin section of the sample (1-2 mm), dip it in a fixing resin (araldite), and eventually shift to a lapping process (a polishing carried out by using abrasive wheels), in order to smooth the surface.
LIMITS OF THE SEM
[1] The thickness of the sample has to be thin in order to allow some of the electron to cross it. It also has to be homogeneous, in order for such electron not to be absorbed or diverted and, thus, dispersed. The SEM is thus inappropriate for the analysis of heterogeneous rocks.
[2] The SEM provides information on the appearance, the nature and the proprieties of the surfaces and the inferior strata of solid samples, but it does not provide information on the internal structure of the sample analysed. For instance, this makes it unusable for thestudy of condrites.
[3] In the SEM, the impact of the electron from the source on the surface to be analysed produces a series of physical side effects that the device is not able to neutralize, thus interfering in the analysis of data. Moreover, the SEM is not powerful enough to interact with particle such as neutrino, which do not react to the electromagnetic interaction produced by the SEM.
HOW G-SEO WORKS
The functioning of G-SEO (Gigantic Scanning Electron Observatory) is based on the high-energy back-reflection (from 5000eV to the energy of the incident beam) of electron from the primary beam, due to the collision of the electron of the same primary beam with the atomic nuclei of the meteoritic finding. This collision generates peculiar traces of light that are registered and provide information about every incident atom, making it possible to determine its composition with absolute accuracy.
In order to let the interaction take place without any external interference, it is necessary that this latter takes place in a completely neutral space. G-SEO is constituted by a storage of 50000 tons of ultra-pure water, surrounded by 13.146 photomultiplier tubes. The structure measures 61,3 m in lenght and 48,3 m in height.
ADVANTAGES OF G-SEO
[1] The main characteristic of G-SEO is its ability to analyse the entire volume of the finding, and not only a sample. Through an X-ray energy detector, G-SEO maps the energy radiated by a specific element and subsequently maps the global distribution of this element in the total volume of the finding. This possibility is of enormous analytical importance.
[2] G-SEO’s working method refines substantially the outputs of analysis, allowing for the realisation of experiments with unprecedented statistics. The so- called new track selector has a very good reproducibility in position (±1μm) and angle (±3mrad), with the possibility to reconstruct all the tracks in a view of 150×150μm2 and 1mm of thickness. This allows a complete scanning of a full spectrum of rocks both in size and composition.
[3] G-SEO data outputs are 100% safe and secured. An online monitor computer located in the control room reads data from the DAQ host computer and it provides shift operators with a flexible tool for selecting event display features, makes online and recent-history histograms to monitor detector performance, and performs a variety of additional tasks needed to efficiently monitor status and diagnose detector and DAQ problems. Events in the data stream can be skimmed off and elementary analysis tools can be applied to check data quality during calibrations or after changes in hardware or online software.
DISADVANTAGES OF G-SEO, FUTURE STEPS AND CONCLUSIONS
As demonstrated in this essay, G-SEO’s potentialities are extremely vast. Nevertheless, the device presents some disadvantages that are linked mainly to the cutting-edge newness of its technology.
[1] G-SEO is expensive, large and must be housed in an area free of any possible electric, magnetic or vibration interference. Maintenance involves keeping a steady voltage, currents to electromagnetic coils and circula- tion of cool water.
[2] Special training is required to operate a G-SEO, as well as to read its outputs.
[3] G-SEO carries a risk of radiation exposure associated with the electrons that scatter from beneath the sample surface. Even though it is designed to prevent any electrical and magnetic interference, which should eliminate the chance of radiation escaping the chamber. G-SEO operators and researchers are advised to observe safety precautions.
The resolution of these problems is one of the future steps that scientists at IEMS are called to meet. G-SEO has already proved to be a unique and irreplaceable tool within the IEMS’ research frame,but there are no reasons to doubt that by further exploration of G-SEO,the whole field of Comparative Planetology could be expanded.
To conclude, the immeasurable wealth of knowledge which could be gained through a further exploration of meteoritic matter is one of the better reasons to keep on investing on the implementation of G-SEO. Moreover, we must not forget that almost every new technology used in commercial or military aircraft has been pioneered by the space industry. Many sophisticated new technologies would not have been successful and would have been abandoned if spacecraft had not given them a profitable application in space research and exploration.
In order to let the interaction take place with-out any external interference, it is necessary that this latter takes place in a neutral space. G-SEO is constituted by a storage of 50000 tons of ultra-pure water, surrounded by 13.146photomultiplier tubes. The structure measures 61,3 m in length and 48,3 m in height.
Author: John Fergusson
Authoritativeness: IEMS G–SEO engineer
Title: Study of the meteorites: the implementation of G–SEO (Gigantic Scan. Electron Observatory)
Editorial assistant: Loredana Alicante
Year: 1995
Field of research: Engineering, research
Previously publication: IEMS, How G–SEO works
The essay was written for the book Ferox, The Forgotten Files: A Journey to the Hidden Moon of Mars 1976–2010 co-published by Skinnerboox and Ciao Press.
The book retraces the story of the International Exploration for the Mars Surrounding (IEMS) – a united program responsible for the civilian space program as well as aeronautics research for the surface of Ferox, the third moon of Mars. Between 1976 and 2010, scientists around Europe worked for IEMS in order to determine the presence of water on Ferox. After their third failure, the mission disappeared.
Read more about IEMS at iems-ferox.com.
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