Near-Earth object

Since ordinary chondrites account for —80% of all meteorite falls (Table 1), it was once believed that their parent bodies were common in the main asteroid belt. However, spectral studies show that most asteroids are dark and featureless (C and related types), and most of the brighter S type differ from ordinary chondrites. H group chondrites probably come from one or more S-type asteroids, possibly 6 Hebe (Burbine et al, 2002). Ordinary chondrites are probably rare in the main part of the asteroid belt (Meibom and Clark, 1999), though they may account for —20% of the near-Earth objects (Binzel et al, 2002). A few ordinary chondrites including Tieschitz (Figure 1(a)) do not fit comfortably into the H, L, and LL groups and may be derived from separate bodies. 

Advanced by Massachusetts Institute of Technology Professor Richard P. Binzel in 1995, the Torino scale is a revision of the Near-Earth Object Hazard Index. In 1999, the International Conference on Near-Earth objects adopted the scale at a meeting in Turino (Turin), Italy (from which the name of the scale is derived). The Torino scale is used to portray the threat to Earth of an impact with a particular comet or asteroid. The measurement scale is based upon agreement between scholars as a means to categorize potential hazards. 

As of March 2003, with approximately a third of Near-Earth objects identified, no object rating more than a 1 on the Torino scale has yet been detected. For example, during February 2002, an asteroid designated 2002 CUl 1 was classified as a 1 on the Torino scale (a green code). Extrapolations of the orbital dynamics of the asteroid and the Earth indicated a low probabilify (approximately 1 in 9,000) of a potential collision in 2049. 

Other Near-Earth objects may be manmade. In 2003 astronomers armounced the tracking of an object designated J002E3 (first discovered in 2002). The object was thought to be either a small asteroid captured by the Earth s gravity, or a discarded rocket casing. 

Lewis, John S. Comet and Asteroid Impact Hazards on a Populated Earth Computer Modeling. Academic Press, 1999. Remo, John L., ed. Near-Earth Objects The United Nations Conference on Near-Earth Objects (Annals of the New York Academy of Sciences V. 822). New York New York Academy of Sciences, 1997. 

NASA Jet Propulsion Laboratory, California Institute of Technology. Near-Earth Objects [cited March 10, 2003]. . 

Near-Earth Object Comet or asteroid that follows orbits that cross the path of the Earth and is a candidate for a possible impact event. 

Near-Earth Object (NEO) Asteroid or comet whose orbit comes near or crosses the orbit of the Earth. 

Missions to the planets of onr solar system and their satellites will increasingly require the greatest possible productivity and scientific return on the large investments already made in the development and lannch of these sophisticated spacecraft. Particular destinations, such as the seas of Emopa, will place great demands on autonomous systems, which will have to conduct independent explorations in environments where communication with Earth is difficult or impossible. Proposed missions to near-Earth objects (NEOs) will entail autonomous rendezvous and proximity operations, and possibly contact with or sample retrieval from the object. 

Near-Earth Objects (NEOs) are comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth s neighborhood. Composed mostly of water ice with embedded dust particles, comets originally formed in the cold outer planetary system while most of the rocky asteroids formed in the warmer inner solar system between the orbits of Mars and Jupiter. 

Empedocles s theory of the four elements was to dominate Western thought for nearly two and a half millennia. It wasn t until the eighteenth century that it was overthrown, because it was endorsed by Aristotle, whose authority was so great that his dogmas often impeded scientific progress. Aristotle added a fifth element, of which the heavenly bodies were supposedly composed. But he agreed with Empedocles that all earthly objects were made of earth, air, fire, and water. 

Salts seem to be nearly as widespread as ice (though not as abundant) in the Solar System, being present on nearly every object where ice has also been observed and where indications of a watery past are in evidence (Enceladus is the key exception so far). There are very few instances (Venus is the most notable one) where salts occur on worlds where H2O is absent or nearly absent. This is a striking correlation, given the terrestrial situation of most evaporites, which are mostly associated with hot and arid areas of Earth. Even so, notable instances of ice-associated evaporites also occur on Earth. In detail, each world and the paragenesis of its salts tells a different story. The key point here is that in this Solar System, salts commonly are associated directly with ice. Hence, phase equilibria generally are described by FREZCHEM, even if on Earth some of the most important evaporite deposits were not formed in the presence of ice or icy-cold conditions. 

The Moon s repertoire of geochemical processes may seem limited, but it represents a key link between the sampled asteroids (see Chapters 1.05 and 1.11) and the terrestrial planets. Four billion years ago, at a time when aU but monocrystalline bits of Earth s dynamic crust were fated for destruction, most of the Moon s crust had already achieved its final configuration. The Moon thus represents a unique window into the early thermal and geochemical state of a moderately large object that underwent igneous differentiation in the inner solar system, and into the cratering history of near-Earth space. 

The attractive force of gravity for objects near Earth s surface increases as you move toward Earth s center. Suppose you are transported from a deep mine to the top of a tall mountain. 

Echoes from 37 main-belt asteroids (MBAs) and 58 near-Earth asteroids (NEAs) have provided a wealth of new information about these objects sizes, shapes, spin vectors, and surface characteristics such as decimeter-scale morphology, topographic relief, regolith porosity, and metal concentration. During the past decade, radar has been established as the most powerful Earth-based technique for determining the physical properties of asteroids that come close enough to yield strong echoes. 

In Earth s upper atmosphere (and, in planetary probe missions, the atmospheres of other planets), atmospheric composition can be measured in situ with mass spectrometers and related instrumentation. However, UV measurements provide a capability for remote sensing of atmospheric composition and its variation with altitude, geographic location, and time, which supplements and extends in situ measurements where available, and can be applied to many objects not yet visited by spacecraft (e.g., in observations of other planets by spacecraft in near-Earth orbit). In addition to atmospheric composition, UV measurements can remotely sense the atmospheric temperature structure and its spatial and temporal variations. Also, information on the fluxes, energies, and spatial distributions of incoming energetic particles (such as those that produce Earth s polar auroras) can be obtained. 

Orbital debris is classified as man-made debris in near Earth orbit v nth a mass typically greater than several grams. The orbital altitude for the majority of these objects ranges between 700 km and 2000 km, but it is possible for the debris to be in orbits higher and lower than those altitudes. Figure 10-14 is an example of the altitude dependence of the flux data. 

Basically, a lever is a solid object with an axis about which it rotates (fulcrum). As the lever rotates about its fulcrum, a point on the lever farther from the fulcrum moves a greater distance. The conservation of energy applied to the lever results in the fact that the output force times its distance from the fulcrum equals the input force times its distance from the fulcrum. A little experience lifting heavy loads with a lever soon teaches one that to maximize the output force, the load should be placed as close to the fulcrum as possible and the input force as far from the fulcrum as possible. To dramatize the nearly infinite possibility of the lever to magnify force, Aixhimcdcs said that if he had a lever long enough and somewhere to stand, he could move Earth. 

There are several factors to consider when using a LGS. First, beacons are formed within the earth s atmosphere, near the telescope aperture. As a result, they don t sample the full telescope aperture when focused on object at infin-... 

The mass of an object is directly associated with its weight. The weight of a body is the pull on the body by the nearest celestial body. On earth, the weight of a body is the pull of the earth on the body, but on the moon, the weight corresponds to the pull of the moon on the body. The weight of a body is directly proportional to its mass and also depends on the distance of the body from the center of the earth or moon or whatever celestial body the object is near. In contrast, the mass of an object is independent of its position. At any given location, for example on the surface of the earth, the weight of an object is directly proportional to its mass. 

This the reverse of the process occurring in Equation 6.1, the decay of 14C, and results in a nearly constant concentration of 14C in the atmosphere. Any living organic synthesis on Earth, such as photosynthesis, will then capture the 14C and produce a 12C/14C ratio in living things to be fixed. When a tree is used for wood in an object such as a museum artefact then the 12C/14C ratio changes and the age of the sample can be calculated using Equation 6.5 as before. 

Sedimentary Rocks,— No sooner does the solidified igneous rock find itself at or near the earth s surface than it becomes the object of the group of processes known as Veathering." This is a subject that has been nearly at a standstill since the publication of Merrill s Rocks, rock... 

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