A brief history of spacecraft missions to asteroids and protoplanets

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There are hundreds of thousands of known asteroids, yet only 14 have been visited by spacecraft thus far, and 9 of those were targets of opportunity. The remaining five asteroids (Braille, Eros, Itokawa, Vesta, and Ceres) were visited by four missions dedicated to asteroid research (Deep Space 1, NEAR-Shoemaker, Hayabusa, and Dawn, respectively). In fact, of these five asteroids, Vesta and Ceres are perhaps better defined as protoplanets because of their sizes and the emerging evidence for their physical and chemical evolution. Two more near-Earth asteroids will be visited in 2018, followed by even more visits in 2023 and 2030. This asteroid mission chronology is listed in Table 1.1. This chapter will tell the story of these asteroid missions and visit each of them in turn to briefly review some of the exciting science results. The story begins with asteroid 951 Gaspra and continues down the list in Table 1.1, according to the target asteroid name presented in chronological order.

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Primitive Meteorites and Asteroids: Physical, Chemical, and Spectroscopic Observations Paving the Way to Exploration

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