Returned comet samples

Brownlee, D. and 181 coauthors ( ) (2006) Comet 81 P/Wild2 under a microscope. Science 314, 1711-1716. This fascinating article, plus the more focused articles that follow it in the same issue, provide the first characterization of comet dust samples collected and returned by the Stardust spacecraft. 

Spacecraft simultaneously in the Jovian system. Additionally, the decadal survey recommended that NASA should select its fourth mission in the New Frontiers program from among the following mission concepts Comet Surface Sample Return, Lunar South Pole Aiken Basin Sample Return, Saturn probe, Trojan Tour and Rendezvous, and Venus In Situ Explorer. 

Stardust February 7, 1999, saw the start of NASA s Stardust mission the cometary probe, the first mission to collect cosmic dust and return the sample to Earth, has a time-of-flight mass spectrometer (CIDA, Cometary and Interstellar Dust Analyser) on board. This analyses the ions which are formed when cosmic dust particles hit the instrument s surface. In June 2004, the probe reached its goal, the comet 8 IPAVild 2, getting as close as 236 km The CIDA instrument, which was developed at the Max Planck Institute for Extraterrestrial Physics in Garching (near Munich), studied both cometary dust and interstellar star dust. 

Star formation and the formation of star systems with planets around them, constantly takes place in dense interstellar clouds. The material present in these clouds is incorporated into the objects that are formed during this process. Pristine or slightly altered organic matter from the cloud from which our solar-system was formed is therefore present in the most primitive objects in the solar system comets, asteroids, and outer solar-system satellites. Pieces of asteroids (and perhaps comets) can be investigated with regards to these components through the analyses of meteorites (and eventually in samples returned from these bodies by spacecraft) in laboratories on Earth. The infall of asteroid and comet material from space may have contributed to the inventory of organic compounds on primordial Earth. 

Cosmochemistry is the study of the chemical composition of the universe and the processes that produced those compositions. This is a tall order, to be sure. Understandably, cosmochemistry focuses primarily on the objects in our own solar system, because that is where we have direct access to the most chemical information. That part of cosmochemistry encompasses the compositions of the Sun, its retinue of planets and their satellites, the almost innumerable asteroids and comets, and the smaller samples (meteorites, interplanetary dust particles or IDPs, returned lunar samples) derived from them. From their chemistry, determined by laboratory measurements of samples or by various remote-sensing techniques, cosmochemists try to unravel the processes that formed or affected them and to fix the chronology of these events. Meteorites offer a unique window on the solar nebula - the disk-shaped cocoon of gas and dust that enveloped the early Sun some 4.57 billion years ago, and from which planetesimals and planets accreted (Fig. 1.1). 

We will now describe each of the various kinds of meteoritic samples available for cosmochemical investigation, progressing from primitive materials to samples from differentiated bodies. Presolar grains extracted from meteorites have already been described in Chapter 5, and interplanetary dust particles (IDPs) and returned comet samples will be described in Chapter 12. 

Figure 8.12 (a) Photograph of Wild 2 comet taken by the Stardust spaceship and (b) a close-up view of a cometary particle captured into aerogel and brought back to Earth in the Stardust Sample Return Canister. (Pictures by courtesy of NASA)... 

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. 

Sample returns from additional comets, outer main belt and Trojan asteroids, and Kuiper Belt objects representing distinct regions of the early Solar System. 

Fortunately, and perhaps surprisingly, the Universe provides a means to address these important questions. Today we are witnessing as the answers emerge to these age-old questions. We now know that asteroids and comets of the Solar System have preserved a detailed record of the dramatic events that four billion years ago gave birth to our planetary system in only a few million years. Gravity and radiation pressure conspire to deliver almost pristine samples of the early Solar System to Earth in the form of meteorites and interplanetary dust particles. We have also taken this process one step further with the successful return of particles from the coma of comet Wild 2 by NASA s Stardust mission. Detailed chemical and mineralogical analyses of these materials allow for the reconstruction of the history of our planetary system. 

The obvious source of comet samples is by direct collection at a comet with Earth return. Stardust, the first comet sample mission (Brownlee et al., 2000), will collect the positively identified particulate samples from a comet and return them to Earth. Stardust, a NASA Discovery mission, will collect thousands of particles from the coma of SP comet Wild 2 and return them in 2006. Hopefully future sample return missions will, in addition, recover subsurface samples of ice and dust and return them to Earth with cryogenic preservation. 

Brownlee D. E. (1996) STARDUST comet and interstellar dust sample return mission. In Physics, Chemistry, and Dynamics of Interplanetary Dust (eds. B. A. S. Gustafson and M. S. Manner). Am. Inst. Phys., New York, pp. 223-226. 

To date, there exists very little quantitative information concerning oxygen isotope compositions in major solar system reservoirs that is obtained by remote (spectroscopic) observation or spacecraft measurements. A measurement of water ice from comet P/Halley, made by the Giotto mission, yields = 12 75 %o (Balsiger et al. 1995 Eberhardt et al. 1995) but no measurement of is available. Precise data are obtained for the Moon, of course, from returned Apollo samples, and the oxygen isotope composition of Mars and the largest asteroid, Vesta, may be inferred from laboratory... 

Origin of solar system water Assessment of the degree of the isotopic variability of water on various solar system bodies is essential to understanding the origin of water in our solar system. Remote isotopic analysis of water (and other species) from more comets, as well as the analysis of returned, pristine cometary samples is required. Further analysis of meteorite samples with modern analytical techniques is also crucial. Specifically, H isotopic variability of water over micron scales in primitive meteorites must be confirmed by further analysis, because it is this observation that is driving the direction of models of water evolution in the solar system. 

Of course, it must be underlined here that appUcarimis in space are not at aU Umited to thermal insulation. Indeed, silica aerogels can be applied to collect aerosol particles [129], to protect space mirrors, or to design tank trifles [130, 131]. The appUcarimis in space were reviewed by Jones [132] (Part XI). The most recent project. Stardust, successfully returned to earth in January 2006. This mission provided samples of a recently deflected comet named Wild-2, which are being examined in various laboratories all over the world. 

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. 

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