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 constant, and pressure and density
refer to the gas.]
|