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A meteoroid (/ ˈ m iː t i ə r ɔɪ d / MEE-tee-ə-royd) [1] is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. [2] Objects smaller than meteoroids are classified as micrometeoroids or space dust.
These lists contain the Sun, the planets, dwarf planets, many of the larger small Solar System bodies (which includes the asteroids), all named natural satellites, and a number of smaller objects of historical or scientific interest, such as comets and near-Earth objects.
The size and shape of asteroids vary significantly, ranging from small rubble piles under a kilometer across and larger than meteoroids, to Ceres, a dwarf planet almost 1000 km in diameter. A body is classified as a comet, not an asteroid, if it shows a coma (tail) when warmed by solar radiation, although recent observations suggest a continuum ...
Outside the top four, the ranking of all the asteroids is uncertain, as there is a great deal of overlap among the estimates. The largest asteroids with an accurately measured mass, because they have been studied by the probe Dawn, are 1 Ceres with a mass of (939.3 ± 0.5) × 10 18 kg, and 4 Vesta at (259.076 ± 0.001) × 10 18 kg.
The number of asteroids brighter than H = 25, which corresponds to about 40 m (130 ft) in diameter, is estimated at 840,000 ± 23,000 —of which about 1.3 percent had been discovered by February 2016; the number of asteroids brighter than H = 30 (larger than 3.5 m (11 ft)) is estimated at 400 ± 100 million—of which about 0.003 percent had ...
At 1 AU meteoroids bigger than 1 mm in size are in a collisional steady state. The significant excess of smaller meteoroids is due to the input from comets. Models of the interplanetary dust environment of the Earth result in 80-90% of cometary dust vs. only 10-20% of asteroidal dust.
These features were caused by the collision of meteors (consisting of large fragments of asteroids) or comets (consisting of ice, dust particles and rocky fragments) with the Earth. For eroded or buried craters, the stated diameter typically refers to the best available estimate of the original rim diameter, and may not correspond to present ...
Solid objects smaller than one meter are usually called meteoroids and micrometeoroids (grain-sized), with the exact division between the two categories being debated over the years. [237] By 2017, the IAU designated any solid object having a diameter between ~30 micrometers and 1 meter as meteoroids, and depreciated the micrometeoroid ...