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FIGURE 4.1 Asteroids and comet nuclei visited by spacecraft as of 2010. SOURCE: Montage by Emily Lakdawalla. Ida, Braille, Annefrank, Gaspra, Borrelly: NASA/JPL/Ted Stryk. Steins: European Space Agency/OSIRIS team. Eros: NASA/Johns Hopkins University Applied Physics Laboratory. Itokawa: Institute of Space and Astronautical Science/Japan Aerospace Exploration Agency/Emily Lakdawalla. Mathilde: NASA/Johns Hopkins University Applied Physics Laboratory/Ted Stryk. Lutetia: ESA/OSIRIS team/Emily Lakdawalla. Halley: Russian Academy of Sciences/Ted Stryk. Tempel 1, Hartley 2: NASA/JPL/University of Maryland. Wild 2: NASA/JPL.

returned to Earth by spacecraft missions or obtained as a result of the vagaries of celestial mechanics. The least-processed of these samples contain small amounts of tiny presolar grains, whose properties and compositions constrain astrophysical processes that predate the solar system.

These processes encompass the inner workings of stars and the formation and modification of materials in the cold reaches of interstellar space.

Specific objectives for continued advancement of studies of primitive bodies in the coming decade include the following:

• Understand presolar processes recorded in the materials of primitive bodies;

• Study condensation, accretion, and other formative processes in the solar nebula;

• Determine the effects and timing of secondary processes on the evolution of primitive bodies; and

• Assess the nature and chronology of planetesimal differentiation.



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