dust/gas ratio - In the solar nebula, the amount of condensed matter ("dust") is relatively small compared to the amount of gas -- chiefly H and He. The dust/gas ratio increases as temperature decreases and more condensed material becomes stable. Researchers usually refer to an elevated dust/gas ratio to describe a system that has a non-cosmic composition which is depleted in gas compared to rocky or icy components. An elevated dust/gas ratio implies that dust was locally concentrated by some mechanism. Vaporization of such dust would enrich the gas in those components present in the dust, resulting in a gas of non-solar composition.
planetesimal - This refers to a small planetary body in the early solar system. Planetesimals are the smaller bodies that must have formed before larger objects such as planets, moons, asteroids, etc., accreted.
protoplanet - This refers to a larger planetary body that has not yet fully accreted into a planet. Such objects can have atmospheres.
mach number - This is the speed of an object relative
to the speed of sound in the medium traversed by the object. Mach
1 is equivalent to the speed of sound, Mach 2 is twice the speed of sound,
etc. An object moving faster than the speed of sound will create
a shock wave. [For an ideal gas, the speed of sound v = sqrt(gamma
* pressure / density), where gamma = a physical constant, and pressure
and density refer to the gas.]
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The X-wind model for chondrule and CAI formation. The wedge-shaped reddish and yellow areas represent the solar nebula disk, here seen along the mid-plane. The disk is wedge-shaped owing to a balance between gravity and gas pressure; pressure (and temperature) increases towards the midplane. Theoretical models suggest that magnetic effects will prevent the nebula disk from extending close to the sun. The inner point of the disk corresponds to the "X point", where material can be moved outwards by an electromagnetic-powered "X-wind" far over the disk, where it can resettle back to the nebula midplane. The X-point will be hot and irradiated, and is the favored location for forming CAIs. Chondrules may have formed at the same place, or more likely (as shown by the graphic) within the disk.