ANSWERS: 4
  • Link: http://www.aerospaceguide.net/whatisanasteroid.html Copy and Paste: Asteroid: A relatively small, inactive body, composed of rock, carbon or metal, which is orbiting the Sun. Comet: A relatively small, sometimes active object, which is composed of dirt and ices. Comets are characterized by dust and gas tails when in proximity to the Sun. Far from the Sun it is difficult to distinguish an asteroid from a comet. Meteoroid: A small particle from an asteroid or comet orbiting he Sun. Meteor: A meteoroid that is observed as it burns up in the Earth's atmosphere - a shooting star. Meteorite: A meteoroid that survives its passage through the Earth's atmosphere and impacts the Earth's surface.
  • 1) "A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's (or another body's) atmosphere is called a meteor, or commonly a "shooting star" or "falling star." If a meteoroid reaches the ground, it is then called a meteorite. Many meteors are part of a meteor shower. The root word meteor comes from the Greek meteōros, meaning "high in the air." " "- Meteoroid: The current official definition of a meteoroid from the International Astronomical Union is "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom." The Royal Astronomical Society has proposed a new definition where a meteoroid is between 100 µm and 10 m across. The NEO definition includes larger objects, up to 50 m in diameter, in this category. Very small meteoroids are known as micrometeoroids (see also interplanetary dust). The composition of meteoroids can be determined as they pass through Earth's atmosphere from their trajectory and the light spectra of the resulting meteor. Their effects on radio signals also yield information, especially useful for daytime meteors which are otherwise very difficult to observe. From these trajectory measurements, meteoroids have been found to have many different orbits, some clustering in streams (see Meteor showers) often associated with a parent comet, others apparently sporadic. The light spectra, combined with trajectory and light curve measurements, have yielded various compositions and densities, ranging from fragile snowball-like objects with density about a quarter that of ice, to nickel-iron rich dense rocks. A relatively small percentage of meteoroids hit the Earth's atmosphere and then pass out again: these are termed Earth-grazing fireballs. Millions of meteors occur in the Earth's atmosphere every day. Most meteoroids that cause meteors are about the size of a pebble. They become visible between about 40 and 75 miles (65 and 120 kilometers) above the earth. They disintegrate at altitudes of 30 to 60 miles (50 to 95 kilometers). Meteoroids travel around the sun in a variety of orbits and at various velocities. The fastest ones move at about 26 miles per second (42 kilometers per second). The earth travels at about 18 miles per second (29 kilometers per second). Thus, when meteoroids meet the Earth's atmosphere head-on, the combined speed may reach about 44 miles per second (71 kilometers per second). - Meteor: A meteor is the visible streak of light that occurs when a meteoroid enters the Earth's atmosphere. Meteors typically occur in the mesosphere, and most range in altitude from 75 km to 100 km. For bodies with a size scale larger than the atmospheric mean free path (10 cm to several metres) the visibility is due to the air friction that heats the meteoroid so that it glows and creates a shining trail of gases and melted meteoroid particles. The gases include vaporized meteoroid material and atmospheric gases that heat up when the meteoroid passes through the atmosphere. Most meteors glow for about a second. Meteors may occur in showers, which arise when the Earth passes through a trail of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific single cause." Source and further information: http://en.wikipedia.org/wiki/Meteoroid 2) "Meteor showers, some of which are known as "meteor storms" , or "meteor outbursts" are celestial events in which a number of meteors are observed to radiate from one point in the sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speed on parallel trajectories. Most are smaller than a grain of sand, so almost all meteoroids disintegrate and never hit the earth's surface. Fragments which do contact Earth's surface are called meteorites." Source and further information: http://en.wikipedia.org/wiki/Meteor_showers 3) "A comet is a Small Solar System Body that orbits the Sun. When close enough to the Sun, a comet exhibits a visible coma (fuzzy "atmosphere"), and sometimes a tail, both because of the effects of solar radiation upon the comet's nucleus. Comet nuclei are themselves loose collections of ice, dust and small rocky particles, ranging from a few kilometers to tens of kilometers across." Source and further information: http://en.wikipedia.org/wiki/Comet 4) "Small Solar System Body (SSSB) is a term defined in 2006 by the International Astronomical Union to describe objects in the Solar System that are neither planets or dwarf planets: All other objects orbiting the Sun shall be referred to collectively as "Small Solar System Bodies" ... These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies. This encompasses all minor planets other than those reclassified as dwarf planets, i.e.: the classical asteroids, with the exception of Ceres; the centaurs and Neptune trojans; the trans-Neptunian objects, with the exception of Pluto, Haumea, Makemake and Eris; all comets." "It is not presently clear whether a lower size bound will be established as part of the definition of Small Solar System Bodies in the future, or if it will encompass all material down to the level of meteoroids, the smallest macroscopic bodies in orbit around the Sun. (On a microscopic level there are even smaller objects such as interplanetary dust, particles of solar wind and free particles of hydrogen.) Except for the largest which are in hydrostatic equilibrium, moons differ from Small Solar System Bodies not in size, but in their orbits. Moons' orbits are not centered around the Sun but around other Solar System objects such as a planets, dwarf planets, and even Small Solar System Bodies themselves. Some of the larger Small Solar System Bodies may be reclassified in future as dwarf planets, pending further examination to determine whether or not they are in hydrostatic equilibrium. The orbits of the vast majority of Small Solar System Bodies are located in two distinct areas, namely the asteroid belt and the Kuiper belt. These two belts possess some internal structure related to perturbations by the major planets (particularly Jupiter and Neptune, respectively), and have fairly loosely defined boundaries. Other areas of the solar system also encompass small bodies in smaller concentrations. These include the near-earth asteroids, centaurs, comets, and scattered disc objects." Source and further information: http://en.wikipedia.org/wiki/Small_Solar_System_body
  • I posted this further answer because of the comment thread to this answer: http://www.answerbag.com/a_view/6684689 It illustrates that some definitions could still be unclear... "From Asteroids to Meteoroids to Meteors to Meteorites Guess what? The International Astronomical Union (IAU) has formally-approved the word "meteor" to be used as BOTH the term for the solid object, as well as, the light-phenoma that it produces. For years I've been told that the term "meteor" only applies to the light phenomenon that we see high in the night sky, but not to the physical object that is falling from space. I was told that the International Astronomical Union (IAU) convened a committee titled "Commission 22" to officially define terms for meteoric objects such as these. This Commission also defined all of the other meteoric and meteoritic "m-words", such as, "meteoroid". Now in this particular case, we have the term "meteoroid" being applied to the very same physical object that could produce a meteor, (were this piece of debris to fall through the Earth's atmosphere). The explanation for this apparent dual usage is that, as long as the solid object is orbiting in interplanetary space, it can be called a "meteoroid". Hence, the word "meteoroid" could not be used for that same object while it is moving through the atmosphere. But this restrictive definition for the terms "meteor" and "meteoroid" resulted in there being no officially-approved word for the solid particle that produces the light phenomenon. At least, that appeared to be the case to me. That is, until recently, when I read on-line the IAU definition for "meteor". It appears that, either there was a recent change in the IAU definition, or that Commission 22 had originally intended that there be a more general usage for the term "meteor" that included the physical object that produces the light phenomenon. See below: Definition of terms by the IAU Commission 22, 1961. - A. meteor: in particular, the light phenomenon which results from the entry into the Earth's atmosphere of a solid particle from space; more generally, as a noun or an adjective, any physical object or phenomenon associated with such an event. - B. meteoroid: a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom or molecule. - C. meteorite: any object defined under B which has reached the surface of the Earth without being completely vaporized. - D. meteoric: the adjectival form pertaining to definitions A and B. - E. meteoritic: the adjectival form pertaining to definition C. - F. fireball: a bright meteor with luminosity which equals or exceeds that of the brightest planets. - G. micrometeorite: a very small meteorite or meteoritic particle with a diameter in general less than a millimeter. Where do we go from here? From here on we need to embrace the [original] concept, as defined by the IAU, that a meteor is BOTH the physical object that enters into the Earth's atmosphere, as well as, the light phenomenon that it produces. Here is a link to a website for IAU Definitions, that can be used as a reference for details on terms and terminology. Relative size of this solar system's planets and planetismals. If you have any questions relating to theNaming of Minor Planets or Small Body Nomenclature, you can submit your terminology questions to IAU Commission 22 " Source and further information: http://meteorite-recovery.tripod.com/2008/mar08.htm Here is the Web page of the commission; http://meteor.asu.cas.cz/IAU/ However, it is under construction and the link "Meteor terminology" is not active.
  • Well, one definition among the sites was:"meteoroid: a solid object in interplanetary space, of a size cnsiderably smaller than an asteroid & considerably larger than an atom or molecule."& then defines micrometeoroid. All the rest required that it orbit the Sun & quite frankly I think they just accidentally left that out. Teacher: What does the asteroid belt consist of? Johnny: asteroids. Teacher: I can only give partial credit for that answer. Mary Lou: I know! I know! It consists of asteroids, meteoroids, & micrometeoroids. Teacher: Right.

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