Symbol
Meaning
Typical unit
Introducing
equation
v r
Rotational velocity
[m s
À1 ]
2.56
v rel
Relative velocity
[m s
À1 ]
3.39
v th
Most probable velocity in an equilibrated
gas
[m s
À1 ]
3.28
v th
Thermal expansion velocity of the gas at the
surface multiplied by a correction factor to
allow for expansion effects
[m s
À1 ]
4.92
v v
Harmonic wavenumber
3.35
V V
Volume of the voids
[m
3
]
2.115
V x
Unperturbed relative velocity at which a
comet encounters planet x
Units of the
planet’s orbital
velocity
1.19
w l
Statistical weight
3.36
W s
Scattered power
[W]
4.20
x
Size parameter
Unitless
4.25
x
Distance along the line of sight towards the
Sun from the plane orthogonal to the
Sun-comet line containing the nucleus
[m]
5.7
X
Anharmonicity constant
3.35
X*
Quantity X (e.g. gas velocity) at the sonic
point
3.71
x 1
Thermal skin depth
[m]
2.105
x i
Effective active fraction of the surface
emitting at the given production rate from
the i
th facet
Unitless
1.24
X Kn
Any macroscopic variable (e.g. density)
3.48
Y
Material strength parameter
2.128
z
Depth below surface or depth of a bed of
material
[m]
2.102,
2.132
z
Distance between the sources
[m]
3.100
Z(T)
Gas emission (sublimation) rate
[molecule m
À2
s
À1
]
2.35
z 0
Particle to surface distance
[m]
4.95
Z i
Mass loss rate per unit area from the i
th facet [molecule m
À2
s
À1
]
1.24
Z T
Partition function
3.37
α
Phase angle
[rad]
2.1
α B , β B
Coefficients in Barker’s equation
[rad]
1.13, 1.14
α D
Doppler line width
[Hz]
3.23
α L
Pressure broadening line width
[Hz]
3.29
α pa
Pitch angle
[rad]
5.19
β
Ratio of radiation pressure force to gravitational force
Unitless
4.72
(continued)
Symbols Used
xxxiii
Meaning
Typical unit
Introducing
equation
v r
Rotational velocity
[m s
À1 ]
2.56
v rel
Relative velocity
[m s
À1 ]
3.39
v th
Most probable velocity in an equilibrated
gas
[m s
À1 ]
3.28
v th
Thermal expansion velocity of the gas at the
surface multiplied by a correction factor to
allow for expansion effects
[m s
À1 ]
4.92
v v
Harmonic wavenumber
3.35
V V
Volume of the voids
[m
3
]
2.115
V x
Unperturbed relative velocity at which a
comet encounters planet x
Units of the
planet’s orbital
velocity
1.19
w l
Statistical weight
3.36
W s
Scattered power
[W]
4.20
x
Size parameter
Unitless
4.25
x
Distance along the line of sight towards the
Sun from the plane orthogonal to the
Sun-comet line containing the nucleus
[m]
5.7
X
Anharmonicity constant
3.35
X*
Quantity X (e.g. gas velocity) at the sonic
point
3.71
x 1
Thermal skin depth
[m]
2.105
x i
Effective active fraction of the surface
emitting at the given production rate from
the i
th facet
Unitless
1.24
X Kn
Any macroscopic variable (e.g. density)
3.48
Y
Material strength parameter
2.128
z
Depth below surface or depth of a bed of
material
[m]
2.102,
2.132
z
Distance between the sources
[m]
3.100
Z(T)
Gas emission (sublimation) rate
[molecule m
À2
s
À1
]
2.35
z 0
Particle to surface distance
[m]
4.95
Z i
Mass loss rate per unit area from the i
th facet [molecule m
À2
s
À1
]
1.24
Z T
Partition function
3.37
α
Phase angle
[rad]
2.1
α B , β B
Coefficients in Barker’s equation
[rad]
1.13, 1.14
α D
Doppler line width
[Hz]
3.23
α L
Pressure broadening line width
[Hz]
3.29
α pa
Pitch angle
[rad]
5.19
β
Ratio of radiation pressure force to gravitational force
Unitless
4.72
(continued)
Symbols Used
xxxiii