UVIS System Scans
Henrik Melin
Don Shemansky
Space Environment Technologies
Planetary and Space Science Division
Observations
• Late 2003 to 2005
• 663 individual scans
• 50230 spectra
• Contains wealth of spatial and temporal
information about the neutrals in the
magnetosphere of Saturn.
Hydrogen
Magnetospheric distribution of Lymanalpha: Pre-SOI East-West profiles
Lyman-alpha
Oxygen
Temporal variability of total oxygen population: Pre-SOI
Variability ~ 2 × 10^27 atoms / second
Oxygen 1304
Normalized line-of-sight intensities
Radial density profile of oxygen
more than double the 18 kms
required to escape the system. React
a net loss of O I, while leaving the population unchanged.
Global loss rate of oxygen due to
The distribution of the
O I density,
δ (x, y, z), can be seen in Figure
charge
exchange
OI
total number of oxygen atoms lost in the charge exchange process, n
be calculated by: Plasma density (next slide)
nloss =
!
0
∞
!
0
∞
!
0
∞
σδe (x, y, z)δOI (x, y, z)|∆vin (x, y)| dx dy dz
re δe (x, y, z) is the volumetric plasma density (Persoon et al., 2006)
he cross section of the OOxygen
+ O+density
charge from
exchange process (Lindsay et
system scans
1), ∆vin (x, y) is the velocity difference between the plasma velocity (
Plasma velocity relative
+ O Charge capture cross-section
to the
velocity
urnOco-rotation
velocity)
and the orbital velocity
andneutral
x, y and
z are spa
Lindsay
et al. 2001
rdinates (as per Section 2.7).
Persoon et al. (2006)
Ion - neutral velocity difference
CC redistribution process
(Kepler’s 3rd law velocity - co-rotation velocity difference)
CC loss process
Lifetime of oxygen
Charge capture loss rate
• Loss rate is 2.5 x 10^28 atoms / second, 10
times required loss rates based on variability.
• Loss rate comparable to H20 source rates
of 2 x 10^28 atoms / second (Burger et al
2007, Hansen et al 2006)
• Variability time-scales of 17 days, comparable
to what is observed
• Peak volumetric loss rate of 2.2 x 10^-3
atoms / cm^3 / second
What’s next?
• XM system scans! First since 2005!
• Short term temporal variability of Ly-alpha
• Refine oxygen density model
• Model hydrogen distribution