WATER-ICE CONTENT
IN TITAN AND CALLISTO
Dunaeva A.N., Kronrod V.A., Kuskov O.L.
Vernadsky Institute of Geochemistry and Analytical Chemistry,
Russian Academy of Sciences,
Moscow, Russia
Callisto
Titan
Callisto and Titan:
were formed in the outer zones of their central planets (Jupiter and Saturn);
 are the largest and well-formed satellites of gas giant planets;
are regular satellites (their orbits and rotation are the same as the rotation of
associated central planets);
 satellites rotation is synchronous with their orbits (like our Moon);
 low density of the satellites suggests that they could contain remarkable
amounts of H2O.
Models of Titan and Callisto.
Callisto:
Titan:
Sohl F. et al., 2003
Grasset et al., 2005
Mitri et al., 2009
Wilson L., 2002
Callisto’s general image
from NASA, JPL
Sohl F., 2010
Titan’s general image from NASA
The initial data for modeling, problem setting
and methods of solution
Physical characteristics of satellites:
- Pressure and temperature at the surface, P[bar] , T [K];
- Gravity acceleration,
g R  [m/s2];
- Radius, R [km]
- Average density, g/cm3
- Mass, M [kg]
- Normalized moment of inertia, I/MR2
Models of the satellites internal structure described by the system of following equations:
 Equations of hydrostatic equilibrium:
dg
 4  G   R   2 g R  R
dR
dP
   R   g R  ,
dR
 The equations of the satellites mass and moment of inertia:
I
n
8
 
15 i 0 i
R  R 
5
5
i
i 1
n
,
4
M   
3 i 0 i
R  R 
3
3
i
i 1
 The equation for calculating ice component concentration in mantle:
Cice 
ice,m  Fe Si   m  
Fe Si = 3.15 - 3.62 g/cm3 (LL-chondrites)
 m  Fe Si  ice,m 
High-pressure water ices equations of state.
 R   density of the
water-ice shell,
 ice,m  average density of
ice in mantle,
 Fe Si  density of the
rock–iron
component,
m
 average density of
mantle
Comparison of Callisto and Titan.
Titan
Tsurf., K
110
93
M,1024g
107.6
134.6
ρ, g/cm3
1.8344
1.881
RP
26.4
20.25
R, km
2410.3
2575.0
I/MR2
0.3549
0.3414
H(ice), km
330
520
Rcore, km
1280
1490
H2O, wt%
47.6-53.8
45.1-51.6
R sat
M
parameters of Callisto
Callisto
H ice
+
T
++
H 2O
RP
+
R core

I/MR 2
I/MR 2
 R core R P H 2 O T H ice M R sat
parameters of Titan
Similar characteristic parameters of Callisto and Titan suggest that satellites could be
built from the identical material and have a similar water/rock ratio (being close to 1).
Water content and density gradients in large icy satellites of
Jupiter and Saturn.
3.6
60
Io
3.2
Ganymede
Europa
Callisto
H2O, wt %
density, g/cm3
Titan
40
20
2.8
2.4
Titan
Ganymede
2
Callisto
Europa
Io
1.6
0
5
10
15
20
25
Orbital distance (in Rplanet)
30
5
10
15
20
25
Orbital distance (in Rplanet)
30
The total content of water in Callisto and Titan
54
1a
Callisto
52
H2O, wt %
10
100
50
200
330
300
10
200
300
48
Titan
400
46
500
44
3
3.2
3.4
3.6
3.8
density of the Fe-Si component, g/cm3
The blue outline is the model of Titan and the black outline is the model of Callisto.
The specks show the range of parameters in which the same content of H2O in satellites is possible.
The solid and dotted lines within the contours are the lines of the satellites water-ice crust equal
thickness (indicated by numbers, in km).
Distance from the satellite's center, km
The internal structure of Titan and Callisto.
Titan
Callisto
2500
2500
water-ice shell
rock-ice mantle
1500
1500
rock-iron core
500
500
“Is Titan just Callisto with weather?”(c) J. Moore
Callisto and Titan located in different planetary systems have similar physical characteristics
and the same internal structure.
Thus, they can be considered as space satellites-twins.
Conclusion.
Titan and Callisto are partially differentiated satellites, consisting, in general, of
an outer ice shell, rock-ice mantle and rock-iron core.
The satellites do not differ in terms of bulk water content which in average is
about 50 wt.%.
The satellites differ just a little from each other in density of rock-iron component
composing of their inner regions. The density of the satellites’ rock material is in
the range of 3.15 - 3.36 g/cm3, which is typical for the hydrated L/LL chondrites.
The equal content of bulk H2O and the same density of the satellites’ rock
material allow to have assumption that ice and rock-icy planetesimals, with the
similar ice and rock composition, were captured into accretion disks of Jupiter and
Saturn, and from this material the satellites of outer planet zone Titan and Callisto
were formed.