Post on 11-Jan-2016
A COMPARISON OF INTERNAL STRUCTURE A COMPARISON OF INTERNAL STRUCTURE
OF GANYMEDE AND TITAN.OF GANYMEDE AND TITAN.
Dunaeva A.N., Kronrod V.A., Kuskov O.L.
Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences,
Moscow, Russia
Ganymede and TitanGanymede and Titan::are the two largest satellites in the Solar System;
were formed in the outer zones of their central planets (Jupiter and Saturn);
are regular satellites (their orbits and rotation are the same as the rotation of associated central planets);
satellites rotation is synchronous with their orbits;
low density of the satellites suggests that they could contain remarkable amounts of H2O.
Jupiter Saturn
Ganymede Titan
The main differences between Ganymede andThe main differences between Ganymede and TitanTitan"Galileo", "Voyager" and "Cassini-Huygens" spacecraft missions to Jupiter and Saturn showed that Ganymede and Titan are different both external and internally:
Ganymede Titan
Atmosphere
Trace oxygen atmosphere Dense nitrogen atmosphere (~400 km): – N2 - 98.4%, CH4 and Ar - 1.6%, – CO2 and other trace organics. – Free oxygen is absent.
Magnetic field
A relatively strong intrinsic magnetic field and magnetosphere.
Intrinsic magnetic field is absent.
Climate
Exogenous climatic processes (evaporation, condensation, precipitation, cycle of substances, seasons) are not available.
The seasonal weather patterns are similar to Earth, but governed by methane cycle (including winds, rains, seasons change, etc.).
Surface features
Two types of terrain: – Very old, highly cratered, dark regions;– Younger (but still ancient), lighter regions marked
with an extensive array of grooves and ridges;Criovolcanism insignificant but important in the
formation of the bright terrain.
The surface is "complex, fluid-processed, and geologically young" (c):
– Ridges, valleys, riverbeds, dunes, stable lakes of liquid hydrocarbons;
– Minor amounts of relatively young impact craters;
– Clearly defined criovolcanism.
Models of Models of Ganymede Ganymede and Titan.and Titan.
Ganymede:
Ganymede’s general image from NASA, JPL
Titan:
Sohl F. et al., 2003
Mitri et al., 2009
Sohl F., 2010 Titan’s general image from NASA
Grasset et al., 2005
2 4 6 8 10
100
150
200
250
300
7 5
1 2 5
1 7 5
2 2 5
2 7 5
3 2 55 0 100 150 200 250
P , k b
T, K
L
IhII
VIVIII
T ita n 's
H Ih = 1 5 0 -1 6 0 k m(m o d e ls w ith o u t in tern a l o cea n )
300 350 400 450 500 550
-150
-100
-50
0
50
-175
-125
-75
-25
25
T ,o C
H , k m
H Ih = 8 0 k mH L = 3 1 0 k m
G an ym ed e's su rfa ce co n d itio n ss
H Ih = 9 5 k mH L = 2 3 0 k m
Phase diagram of water and the temperature distribution Phase diagram of water and the temperature distribution
in the Ganymede’s and Titan’s icy crust.in the Ganymede’s and Titan’s icy crust.
Straight thin lines - conductive temperature profiles through the external (ice-Ih) crust. Dashed lines – adiabatic convective heat transfer in the water subcrustal ocean and in high-pressure ices. H, HIh, HL - the distance from the satellite's surface (depth), the thickness of the external ice-Ih crust and of the inner liquid ocean respectively.
Calculation of the Ganymede's and Titan’s heat fluxCalculation of the Ganymede's and Titan’s heat flux
The thickness of the icy crust and internal ocean of Ganymede (blue) and Titan (black) via the heat flow through the satellites ice-Ih crust.
F(mW/m2) = [o(RSat - НIh) /(Н Ih RSat)]ln[T2 /Т1]
o = 567 W/m - thermal conductivity of ice Ih,
RSat – satellite’s radius,
НIh – thickness of the icy crust,
Т1 – satellite's surface temperature,
Т2 – the temperature at the ice-Ih - liquid phase boundary,
Hw - the thickness of internal ocean,
F – heat flux.
[1] Bland, M.T., et al., 2009
[2] Mitri G., Showman A., 2008
2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0Í Ih , k m
0
5
10
15
20 400 300 250 100H w , k m
F = 5 m W /m 2 [1 ]
F = 2 .9 m W /m 2
F ,m W /m 205 0200 150350
T rip le p o in t
L -Ih -III2 5 1 .1 5 K / 2 .0 7 k b a r
F = 3 .3 m W /m 2
F = 7 m W /m 2 [2 ]
M eltin g p o in ts L -Ih
Physical characteristics of the satellites Ganymede Titan
Pressure at the surface, P[bar] 1.0e-06 1.467
Temperature at the surface, T [K] 110.0 93.0
Gravity acceleration, [m/s2]; 1.428 1.35486
Radius, R [km] 2634.0 2575.0
Average density, g/cm3 1.936 1.88202
Mass, M [kg] 0.14819e24 0.1346e24
Normalized moment of inertia, I/MR2 0.3105 0.3419
Models of the satellites internal structure described by the system of following equations: Equations of hydrostatic equilibrium:
,
The equations of the satellites mass and moment of inertia:
,
The equation for calculating ice component concentration in mantle:
High-pressure water ices equations of state.
RR iii
n
i
I5
1
5
015
8
Initinal data for modeling, problem setting and methods of solutionInitinal data for modeling, problem setting and methods of solution
RgRdRdP RRgRG
dR
dg24
RR iii
n
i
M3
1
3
03
4
miceSiFem
mSiFemiceiceC
,
,
R
Rg
m
density of the water-ice shell,
average density of ice in mantle,
density of the rock–iron component,
average density of mantle
mice,
SiFe
= 3.15 - 3.62 g/cm3 (LL-chondrites)SiFe
The internal structure of The internal structure of Ganymede and Ganymede and Titan.Titan.
820 840 860 880 900T h ick n ess o f th e w a ter-icy sh e ll, k m
500
1500
2500
Dis
tanc
e fr
om G
anim
ede'
s ce
nte
r, k
m
0.384 0.388 0.392 0.396 0.4
I/M R 2 fo r ro ck – iro n co re
G a n y m ed e 's su r fa ce
F e-S i m a n tle
Ih (~95 km)
F e-F eS co re
~ 23 0 k m
3 . 5 3 . 5 5 3 . 6 3 . 6 5
M a n tle d en sity , g /cm 3
~ 4 6 5 k m
core= 5.15 g/cm 3
core= 5.7 g/cm 3
core= 6.5 g/cm 3
V (~55 km)
VI ~ 5 3 0 k m
a)
liq u id o cea n
400 440 480 520
T h ick n ess o f th e w a ter-icy sh e ll, k m
500
1500
2500
Dis
tan
ce f
rom
Tit
an's
cen
ter,
km T ita n 's su rfa ce
ro ck -ice m a n tle
Ih (80 km)liq u id o cea n (~ 3 1 0 k m )
V + V I (~ 1 2 0 k m )
ro ck -iro n co re
In general three-layer models of satellites including the outer water-ice shell, mantle (rock or rock-ice) and the inner core (Fe-Si or Fe-FeS) can be made.
Moreover, two-layer models (without inner core) could be realized. In this case satellite has significant large outer water-icy shell, but its inner core not forms.
On this model the maximum possible thickness of the water-ice shell is about 900 km and 500 km for Ganymede and Titan respectively.
5 10 15 20 25 30Orbital distance (in Rplanet)
0
20
40
60
H2O
, w
t %
IoEuropa
GanymedeCallisto
Titan
Water content and density gradients in large icy satellites of Water content and density gradients in large icy satellites of Jupiter and Saturn.Jupiter and Saturn.
5 10 15 20 25 30Orbital distance (in Rplanet)
1 . 6
2
2 . 4
2 . 8
3 . 2
3 . 6
de
ns
ity,
g/c
m3
Io
Europa
Ganymede CallistoTitan
The total water content in Ganymede is 46-48% , in Titan - 45-52% .
Conclusion.Conclusion.Ganymede and Titan are the similar in size and chemical composition: the density of the satellites’ rock material is typical for the hydrated L/LL chondrites.
The satellites do not differ in terms of bulk water content which in average is about 50 wt.% (water/rock ratio is close to 1).
Ganymede and Titan both may have subsurface oceans. – Internal ocean in the satellites not forms when the heat fluxes less than 3.3
mW/m2 and 2.9 mW/m2 for Titan and Ganymede respectively.
Internal structure of the satellites can differ fundamentally: – Ganymede is a completely differentiated body, with the inner region formed
by separating of the original L/LL-chondritic substance into the silicate mantle and metallic core.
– Titan is differentiated only partially: its inner areas are represented by a mixture of rock and ice components.
Equal content of bulk H2O and the same density of the satellites’ rock material allow to have assumption that Ganymede and Titan could have been formed from the planetesimals with similar composition corresponding to the ordinary L/LL-chondrites. Different conditions of the satellites’ formation from accretion disks led to major differences in their internal structure.