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Asteroids vary greatly in size, from almost 1000 km for the largest down to rocks just 1 meter across, below which an object is classified as a meteoroid. [f] The three largest are very much like miniature planets: they are roughly spherical, have at least partly differentiated interiors, [69] and are thought to be surviving protoplanets.
These are composed primarily of S-type asteroids, whereas the neighboring Hungaria family includes some E-types. [101] The Phocaea family orbit between 2.25 and 2.5 AU from the Sun. [102] Skirting the outer edge of the asteroid belt is the Cybele group, orbiting between 3.3 and 3.5 AU. These have a 7:4 orbital resonance with Jupiter.
While many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia, and water. The Kuiper belt is home to most of the objects that astronomers generally accept as dwarf planets: Orcus, Pluto, [5] Haumea, [6] Quaoar, and Makemake. [7]
Many chondritic asteroids also contained significant amounts of water, possibly due to the accretion of ice along with rocky material. As a result, many chondrites contain hydrous minerals, such as clays, that formed when the water interacted with the rock on the asteroid in a process known as aqueous alteration. In addition, all chondritic ...
253 Mathilde, a C-type asteroid. 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.
Astronomers have detected water molecules on the surface of asteroids for the first time, a surprising find given that the space rocks were thought to be “completely dry.”
A theoretical class of planets, composed of a metal core surrounded by primarily carbon-based minerals. They may be considered a type of terrestrial planet if the metal content dominates. The Solar System contains no carbon planets but does have carbonaceous asteroids, such as Ceres and Hygiea. It is unknown if Ceres has a rocky or metallic core.
Asteroids are somewhat arbitrarily distinguished from many different types of similar objects: small Solar System bodies primarily composed of dust and ice instead of mineral and rock are known as comets; bodies less than one meter in diameter are known as meteoroids; very large asteroids are sometimes called planetoids or planetesimals; and ...