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Active asteroids are objects that have asteroid-like orbits but show comet-like visual characteristics. That is, they show comae , tails , or other visual evidence of mass-loss (like a comet), but their orbit remains within Jupiter 's orbit (like an asteroid).
For most numbered asteroids, almost nothing is known apart from a few physical parameters and orbital elements. Some physical characteristics can only be estimated. The physical data is determined by making certain standard assumptions.
C-type (carbonaceous / ˌ k ɑːr b ə ˈ n eɪ ʃ ə s /) asteroids are the most common variety, forming around 75% of known asteroids. [1] They are volatile-rich and distinguished by a very low albedo because their composition includes a large amount of carbon, in addition to rocks and minerals. They have an average density of about 1.7 g/cm 3.
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.
Nonetheless, collisions between large asteroids occur and can produce an asteroid family, whose members have similar orbital characteristics and compositions. Individual asteroids within the belt are categorized by their spectra, with most falling into three basic groups: carbonaceous , silicate , and metal-rich .
In 1975, astronomers Clark R. Chapman, David Morrison, and Ben Zellner developed a simple taxonomic system for asteroids based on color, albedo, and spectral shape.The three categories were labelled "C" for dark carbonaceous objects, "S" for stony (siliceous) objects, and "U" for those that did not fit into either C or S. [2] This basic division of asteroid spectra has since been expanded and ...
Four huge asteroids — and a fifth that's much smaller — are passing Earth on Thursday in their closest approaches to the planet ever recorded. 4 large asteroids, including 1 the size of a ...
The composition of these asteroids is similar to a variety of stony meteorites which share similar spectral characteristics. Due to their volatile-poor (rocky) composition, S-type asteroids have relatively high density. A survey of 11 S-type asteroids found an average density of 3.0 g/cm 3. [2]