The Stardust Mission

Hypervelocity Particle Capture 32.2.1. Initial on Orbit Studies 

After conducting many ground-based experiments on the feasibility of using aerogels 

The Stardust Mission was designed around the fact that low-density aerogel had been demonstrated to be an excellent hypervelocity particle capture medium [17]. The mission plan was to transport a grid of aerogel cells into space, rendezvous with a comet, capture material from the comet in the aerogel, and return the collected samples to the earth [20]. The primary science requirement of the mission was that 1,000 cometary particles, 15 pm or larger in diameter, be captured and returned to Earth. 

The Stardust spacecraft was launched successfully in February of 1999 from Kennedy Space Center on a Delta launch vehicle. During the cruise phase prior to the comet encounter. 

Gradient density silica aerogel was developed and produced for the Stardust particle capture grids, since it was considered to have superior captiue properties. When high-velocity particles begin to penetrate the gradient density aerogel, they first encounter 

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It is reasonable to consider the assumption that life began, somehow, among one of the mixtures of small organic molecules that are produced by abiotic processes. The only natural examples in hand today are the components of meteorites that have fallen to Earth (see Section 5.2.1) and particles returned by the Stardust mission. Spectroscopy has also yielded partial lists of the organic molecules in interstellar space and interplanetary dust clouds. 

The Stardust mission succeeded in bringing solid particles from the Wild 2 comet to the Earth. Comets are the intriguing celestial bodies that are believed the last witnesses of the formation of the solar system. They are considered to be aggregates of primordial interstellar dust particles, the last reminders of protosolar nebula. Even simple spectroscopic observation indicates that comets are rich in simple organic species, which may undergo further photochemical transformations during their life within the solar system [35, 36], Hundreds of organic molecules... 

With the success of the Stardust mission, tests of our models for solar nebula, and thus protoplanetary disk evolution, are no longer limited to asteroidal bodies (meteorites), but now can be applied to cometary bodies as well. Stardust returned dust grains that were ejected from the surface of comet Wild 2, a Jupiter-family cometthatis thought to have formed at distances of >20 AU from the Sun (Brownlee et al. 2006). Thus, we now have samples of materials from the outer solar nebula that can be studied in detail. 

Among the goals for the Stardust mission was identifying the origin of the crystalline silicates in comets, whose presence in comets had been known from observations of comets Halley and Hale-Bopp (as reviewed in Bockelee-Morvan... 

Figure 5.5 Winds in the solar nebula might be one of the possible processes responsible for the mixing of hot and cold components found in both meteorites and comets. Meteorites contain calcium-aluminum-rich inclusions (CAIs, formed at about 2000 K) and chondrules (formed at about 1650K), which may have been created near the proto-Sun and then blown (gray arrows) several astronomical units away, into the region of the asteroids between Mars and Jupiter, where they were embedded in a matrix of temperature-sensitive, carbon-based cold components. The hot component in comets, tiny grains of annealed silicate dust (olivine) is vaporized at about 1600 K, suggesting that it never reached the innermost region of the disk before it was transported (white arrows) out beyond the orbit of Pluto, where it was mixed with ices and some unheated silicate dust ( cold components). Vigorous convection in the accretion disk may have contributed to the transport of many materials and has been dramatically confirmed by the Stardust mission (Nuth 2001).

In order to consider the processes of dust coagulation in the early Solar System, we first review the characteristics of this material. Of considerable importance is the fact that these samples - represented principally by chondritic meteorites, but also by IDPs and by samples from Comet Wild 2 collected by the Stardust mission - all come from parent bodies of different kinds. As a result, even the most primitive of these materials has been processed, both physically and chemically, to different degrees. The processes that affected Solar System dust may have occurred in different environments such as the solar nebula (e.g. evaporation/condensation, annealing) and asteroidal parent bodies (aqueous alteration and/or thermal processing, mild compaction to extensive lithihcation). A major challenge is to understand the effects of this secondary processing. 

Thus, it is necessary to consider the role of the dust in the ISM. Dust comprises about 1% ofthe mass ofthe material in the ISM and can act as a surface upon which chemistry can occur (Fig. 4). Although we have yet to actually examine a piece of interstellar dust we believe it is similar to that found in the Solar System and recently collected by the Stardust mission. The dust is either carbonaceous or silicate in nature, comprising of small particles, typically sub-microns in size, probably with an irregular (fractal ) structure. Being so cold (around 10 K) the dust grains act as a depository for any gaseous molecules which "stick" to the surface. Hence H atoms may collide with the surface, and subsequent reaction between such H ... 

Finally, let us recall the attempts to measure the 244Pu content in the local ISM, which may have some interesting astrophysical implications. At present, this can be done through the analysis of dust grains of identified interstellar origin recovered in deep-sea sediments (e.g. [52]). In a near future, the determination of elemental and isotopic composition of the ISM grains will be a major goal of research with their recovery to Earth by the Stardust mission [53],... 

The study of the comet particles returned by the Stardust Mission could have been made easier and more comprehensive if aerogels other than silicon dioxide had been used. This is due to the fact that since silicon was the major element in the capture medium and most of the Wild 2 particles fragmented and mixed at the microscopic scale with the aerogel, it was not possible to determine elemental ratios using silicon as the standard, for example, iron to silicon ratio and nickel to silicon ratio. Silicon is typically used as the standard for the determination of elemental abundances in geochemistry and cosmochemis-try, since it is found throughout our planet and the solar system. Since silicon could not be used and iron was used as the standard element for the Stardust geochemical analyses. 

Space science During the Stardust mission (1999-2006), an aerogel array was used to capture cometary and interstellar particles. The particles stayed largely intact when they were smoothly slowed down by the small filaments of the gel network and could be returned to earth for analysis (Jones, 2006). 

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