TABLE 4.1 Major Accomplishments by Telescopes and Space-Based Studies of Primitive Bodies in the Past Decade
|Major Accomplishment||Mission and/or Technique|
|Detailed orbital characterization of an asteroid, including successful landing||Near-Earth Asteroid Rendezvous|
|Sampling of a near-Earth asteroid and return of the sample to Earth; determination that small asteroids can be rubble piles||Hayabusa|
|Determination of the density of a comet nucleus via the first controlled cratering experiment on a primitive body||Deep Impact|
|Return of comet dust for analysis in terrestrial laboratories||Stardust|
|First reconnaissance of a possible former trans-Neptune object in the form of Saturn’s distant satellite, Phoebe||Cassini|
|Discovery that binary objects are common among near-Earth and main belt asteroids and Kuiper belt objects, and that comets occur within the main asteroid belt||Ground- and space-based telescopes and radar studies|
system formation and the nature of the interstellar matter that was incorporated? is largely a question that can be answered only by the study of primitive bodies. The planetary habitats theme also includes the question, What were the primordial sources of organic matter, and where does organic synthesis continue today?—which is also relevant to the study of primitive bodies, because comets are believed to be a primary source of primordial organic materials. In the workings of solar systems theme, two of the questions, in particular, directly involve the primitive bodies: First, primitive bodies are central to the question, What solar system bodies endanger Earth’s biosphere, and what mechanisms shield it? because of the role that asteroid and comet impacts on Earth have played in mass extinction events, and because such impacts still pose a hazard today. How have the myriad chemical and physical properties that shaped the solar system operated, interacted, and evolved over time? is a question that is directly addressed by the study of their role in accretion and subsequent bombardment through time, in particular because the primitive bodies are believed to have served an important role in delivering organic materials and water to the inner planets, particularly Earth.
The goals for research on primitive bodies for the next decade are twofold:
• Decipher the record in primitive bodies of epochs and processes not obtainable elsewhere, and
• Understand the role of primitive bodies as building blocks for planets and life.
Primitive bodies, be they asteroids, comets, KBOs, possibly the martian moons, meteorites, or interplanetary dust particles—are thought to have formed earlier than the planets in the hierarchical assembly of solar system bodies. Because they witnessed, or participated in, many of the formative processes in the early solar nebula, they can provide unique constraints on physical conditions and cosmochemical abundances. Such constraints come, in part, from observations and remote-sensing measurements made from nearby spacecraft. Because it is possible to visit only a small number of the myriad, highly diverse primitive bodies, researchers must also observe them using Earth-based telescopes (Figure 4.1). Constraints on nebular processes, as well as absolute dating of events in the early solar system, also come from laboratory analyses of samples of these bodies, whether collected and