I can see the advantages either way. The final arbiter would be cost and the technological problems in returning a sample consisting of a glob of ice. I also do not know how you would 'land' on the surface to obtain a pristine sample which is what you want for the effort, and not a sample of processed material in the coma.
The NASA Stardust Mission was launched on February 7, 1999 and will rendezvous with Comet Wild-2 (pronounced "Vilt-2" on January 2, 2004. The spacecraft will gather particles flying off the nucleus of the comet. In addition, Stardust will attempt to gather samples from a stream of interstellar dust that flows through the solar system. Captured in a glass foam called aerogel, the comet and interstellar dust samples will be enclosed in a clamshell-like capsule that will be dropped off for reentry into Earth's atmosphere in January 2006. Equipped with parachutes, the capsule will float to a pre-selected spot in the Utah desert, where it will be retrieved and its contents delivered to scientists for detailed analysis.
The spacecraft has also made some discoveries enroute that are quite surprising! According to a JPL Press Release.
Preliminary measurements of interstellar dust particles encountered by NASA's Stardust spacecraft indicate the surprising presence of large tar-like molecules that scientists said could have played an important role in sparking life here on Earth. The finding, if confirmed, could imply that interstellar particles constituted an important delivery system for the molecules necessary for life to begin on Earth billions of years ago. "When they got in contact with liquid water on the young Earth, they could have triggered the type of chemical reactions which are prerequisite for the origin of life," said Jochen Kissel, of the Max Planck Institut fur extraterrestrische Physik, in Garsching, Germany, writing in the latest issue of Sterne und Weltraum, a German-language astronomy magazine.
Don Brownlee, the mission's principal investigator, called the announcement intriguing, but cautioned that the results were preliminary. "There is always the worry there is some unknown about the response of the instrument, but if that is the composition of interstellar particles, it's very exciting," Brownlee said. Kissel and other German scientists working on Stardust's Cometary and Interstellar Dust Analyzer (CIDA) report that five of the macromolecules hit their instrument between February and December 1999. Whenever particles, traveling at speeds of 18 miles (30 kilometers) per second, strike the instrument's impact plate, they are vaporized. An electric field in the front of the plate then draws the positively charged fragments down into the detector. The time the particles take to travel the 5 feet (1.5 meters) to the detector depends on their mass, with the heavier ions taking longer.
In a minute fraction of a second, the instrument measures the pulses and generates a mass spectrum. "It is the size of these molecular fragments with nuclear masses of up to 2,000 (water, for example, has 18 such units) which surprised us as much as the seemingly absence of any mineral constituents," Kissel said. "Only organic molecules can reach that size." The cosmic particles consist mainly of three-dimensionally cross-linked organic macromolecules that resemble tar or coal. As such, the particles could represent one way in which prebiotic molecules arrived on Earth.
Other theories suggest they were delivered via impacts by asteroids or comets or simply formed here, and then went on to play a vital role in the dawn of life. "Many people believe these particles may have been a major component of the primordial soup," Brownlee said.
NASA's $155 million Stardust was launched in February 1999. It will visit the comet Wild-2 in 2004, and return samples of cometary and interstellar dust to Earth two years later.
Copyright 1997 Dr. Sten Odenwald
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