Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Primitive Bodies and the Origin of Life n its earliest youth the solar system I was inhabited by a huge swarm of small rocky and icy bodies called planetesimals, orbiting the Sun in a giant disk. And, although the full details are still being debated (see the section, Formation of the Giant Planets), it is clear that collisions between planetesimals led to the for- mation of increasingly larger objects, with the end result being the planets we know today. Many of the diverse Above: Cometary material bombarding early Earth, as illustrated in this artistâs concept, may have carried organic mate- rials from which life arose. Right: A wide-angle view of the twin tails of Comet Hale-Bopp on the night of March 10, 1997. small bodies now seen in the solar sys- radiation, micrometeorite impacts, found in living systems. Radiation on tem are directly related to the primor- and other processes. By studying the surfaces of planets and their satel- dial population of planetesimals. these changes in a cometâs surface lites can also create and destroy com- Beyond the orbit of Pluto, for material, scientists glean a significant plex organic molecules, but the details example, many small icy objects amount of information about the his- of the required conditions and the bal- remain in their archaic forms. For the tory of the Sun and the solar system, ance between destruction and creation most part these so-called Kuiper Belt much as reading the rings of a tree are not known. Studying the differ- objects and their relatives remain in can teach us about the history of cli- ences between cometary and planetary their orbits far from the Sun. But mate changes on Earth. organic molecules can help scientists every so often, one gets flung into a One change of particular interest to understand this balance by showing new path taking it into the inner solar researchers results from the discovery which molecules are likely to have systemâwe call these objects comets. that complex carbon compounds are come from comets and which have As comets travel through the solar created when a cometâs surface ices been formed by other processes. This system, their surfaces undergo a num- (water, ammonia, carbon dioxide, understanding will provide important ber of changes. The most obvious methane, and so on) are irradiated by insights into the origin and evolution example is the development of the ultraviolet light, high-energy particles of life on Earth. cometâs characteristic tail as the Sun from the Sun, or cosmic rays. Labora- The Comet Surface Sample Return warms the surface ices and causes tory simulations indicate that, when mission emphasizes the return to them to turn from a solid into a exposed to liquid water, such radiation- Earth of a sample of cometary surface vapor. Other physical and chemical processed material produces amino material that will provide the first changes occur owing to the effects of acids and other organic molecules direct set of data on cometary 20 New Frontiers in Solar System Exploration
Comet Surface Sample Return Profile Comet Surface Sample Return Mission Type: Sample Return Cost Class: Medium Priority Measurements: ⢠Characterize the target comet. ⢠Select, document, and return mate- rial collected at one or more sites, preferably in or near an active vent. processes and answer whether the water in comets is very close to the surface. Such a sample will also show if the organic materials we believe to exist there actually do. If they do, then the sample will also give us our first look at ancient organic mole- cules similar to those first brought to our planet by cometary impacts 4 bil- lion years ago. Knowing the nature of these molecules should provide exciting new insights into the origin of life on Earth. The Comet Surface Sample Return (CSSR) mission would address other scientific interests as well. It would provide the first direct data on the dif- ference between a cometâs nucleus and Artistâs impression of the lander portion of the Comet Surface Sample Return space- the relatively well studied material in craft just after it has deployed its twin solar arrays. the cometary tail. In addition, data from this mission would enable scien- Guiding Themes Addressed Important Planetary Science Questions Addressed tists to resolve questions about the wealth of large-mass molecules and The First Billion What processes marked the initial stages of planet and fragments seen by spacecraft in the Years of Solar satellite formation? cloud of gas and dust around Halleyâs System History Are comets near-pristine relics of the early solar system? comet during its last visit to the inner solar system in 1986. Finally, the CSSR mission concept Volatiles and What is the history of volatile compounds, especially water, across the solar system? would give scientists their first look Organics at how a comet is actually put What is the nature of organic material in the solar system, The Stuff of Life and how has this matter evolved? together. Is it really a dirty snowball, as conceived in popular and scientif- What is the chemical composition of materials on a ic imagination? Is a comet a homo- cometâs surface? genous mixture of dust and ices, or What changes the surface of asteroids and comets as they are there pockets of differing materi- travel through the solar system? als scattered throughout its body? If the latter is true, what holds these different pieces together? Studying Processes How do the processes that shape the contemporary character of planetary bodies operate and interact? the structure of the material returned How Planetary What is below the surface on the nuclues of a comet, and by CSSR should answer many of Systems Work how does it relate to what is on the surface and in the tail? these questions. 21