Far-ultraviolet photometric
characteristics of the icy
moons of Saturn
Royer, E.M.1 & Hendrix, A.R.2
1
JPL, Pasadena, CA ; 2 Planetary Science Institute, Tucson, AZ
04/18/2013, JPL
Data Distribution
+ Tethys
Dione
Mimas
Tethys Phase Curve
Dione Phase Curve
Mimas Phase Curve
Phase Curves Comparison
Phase curves improvements
• Better way to take the Solar spectrum into account
• Now, the heliocentric distance is taken into account
• Use of the predicted c-kernels
Mimas
More data at very low phase angles, compare to other sateliites
Is the opposition effect more important on Mimas?
Filing Factor
Ff = Area Body / Pixel Size
Area Body = Body Radius * Body Radius * p
Pixel Size = (2 * altitude * tan(0.00075)) * (2 *
altitude * tan(0.00050))
Ff = 1.3
What if I sum the contributions from 2 or 3 pixels to obtain the reflectance ?
Hapke model
Mimas Leading
Tethys Leading
Dione Leading
Mimas Trailing
Tethys Trailing
Dione Trailing
Phase Function
Porosity
The h term is related to porosity P by the equation (Domingue and Verbiscer, 1997):
h= -(3/8) ln(P) Y
Y is a lunar-like grain size distribution : Y = sqrt(3) / ln(rl/rs), where rl and rs are the effective
radius of the largest and smallest grain respectively
If we assume a uniform grain size distribution and that rl/rs = 1000 , h being equal to 0.066,
we obtain a porosity of about 50 % for the Saturnian satellites.
What is the contribution of the coherent-backscatter ?
Buratti model
A linear superposition of a lunar-like scattering law and a Lambert component
that provide an adequate simple representation of the scattering properties
A is a parameter such that for a lunar-like purely single scattering, A = 1 and
for a diffuse (Lambert) scatterer A = 0.
f(a) is the surface phase function, which express changes in intensity due to
factors such as the single particle phase function and mutual shadowing
among regolith particles.
Tethys Leading: Buratti model