1. Crystalline water ice on the satellite of 2003 EL61
(Catania)
TNO2006
Crystalline water ice on the satellite of 2003 EL61
- Binary TNO covered with almost pure crystalline water ice -
Naruhisa Takato, Hiroshi Terada & Tae-Soo Pyo
( Subaru Telescope)

2. (All) icy satellites show crystalline feature
Satanian satellites
Uranian satellites
Charon
(Brown & Calvin 2000)
(All) icy satellites show crystalline feature
Grundy et al 1999

3. Lead time for crystallization
（Kouchi et al. 1994）
Age of Solar
System ( 78 K )
1 hour
( 144 K )

4. 2003 EL61 Discovered by M. Brown et al. (2005)
e=0.2, i=28°, a=43 AU (q=34 AU)
(scattered disk object?)
One of the largest TNOs
Properties of PRIMARY:
　　rotation period: 3.9 h
　　major aixs：2000～2500 ｋｍ
　　albedo: 0.6～0.7
　　bulk density:(2.6～3.3)×103 kg m-3
(Rabinowitz et al. 2005)

5. (~30% of Pluto+Charon mass）
Two satellites
mp + ms1 = (4.2±0.1)×1021 kg
(~30% of Pluto+Charon mass）
ms1/mp ～1/100 （assuming the same albedo and density）
M. Brown et al. 2005

6. Our observations Subaru telescope＋IRCS 15 Jan. 2006 UT HK grism
Slit width：0.6”
　（seeing 0.3”～0.4”）
Exposure time: ３４００ sec
G2V standard star

7. primary satellite Satellite + sky sky Primary Satellite

8. NH3・H20
D=10μm, T=20K
crystalline
D=30μm, T=20K

9. What means the existence of CRYSTALLINE water ice?
crystallization
amorphization
spattering
gardening
NOTE:
We are seeing only the skin of the object (~100μｍ) .

10. Crystallization Surface event Interior activity
related to the satellite forming event
Heating by micrometeorite impacts
Slow deposition of water-vapor created by micrometeorite impacts.
Heating by collisions with medium size KBOs
4. Heating by radioactive isotope
5. Cryo-volcanic venting
6. Tidal heating
7. Accretion heating
8. Giant impact
9. Materials were already crystallized before accretion.

11. Amorphization by UV photon （Kouchi & Kuroda 1990)
one hour exposure of UV flux ~1014 photon/cm2 s (l= nm) 　can amorphize ~1 mm crystalline ice layer (T=50-70K).
by high energy particles
irradiate 100 mm in depth within ~ 5x108 years
~1 mm layer can be amorphized in ~100 years at 43 AU
Note : UV flux amorphize down to its optical depth (< 1mm)
Cf. Optical depth at l=1.65 mm is ~100 mm

12. Strazzula et al. 2003

13. sputtering by Lyα photon（Westley et al. 1995) 0.003 H20/photon @35K
by high energy particles ( Shi et al. 1995)
0.3 H20/ion for 1keV H+
4.9 x 109 H2O/m2 s @ 43 AU
~ 10-5 mm/year
4.9 x 108 H2O/m2 43 AU
~ 10-6 mm/year

14. Westley et al. 1995

15. Shi et al. 1995

16. Gardening by micrometeorides
assumption：
Dust particle: Grun et al. 1993
mi　= 8 x kg
vi = 26 km/s
Flux : 8 x 10-5 m-2 s-1
Crater size: controled by gravity
density of the surface ice: 0.5 g cm-3
Satellite radius: R=200 km,
bulk density: ～１ g cm-3
　　(escape velocity～１５０ m/s, g~0.067m/s2)
P scaling

17. Time scale to filling the surface with craters (πr2 flux)-1～600 years
Crater radius: ｒ～ 0.5 mm
excavated mass ～1.0 ｘ 10-7 kg
Escaped mass ～ 1.1 ｘ kg
Time scale to filling the surface with craters
　　(πr2　flux)-1～600 years
Depth of 0.5 mm layer is excavated by micrometeorite
impacts in about 600 years

18. Crystallization Surface event Inner activity
related to the satellite forming event
Heating by micrometeorite impacts
Slow deposition of water-vapor created by micrometeorite impacts.
Heating by collisions with medium size KBOs
4. Heating by radioactive isotope
5. Cryo-volcanic venting
6. Tidal heating
7. Accretion heating
8. Giant impact
9. Materials were were already crystallized
before the accretion.

19. Impact shock heating D T 1x10-7 (max 3x10-5) of r /rp
Wada
Solve Rankine-Hugoniot equation
DT > K: r < 5 rp
Crystallize 1x10-14 kg / impact
(if all energy is converted to heat
DT=50, then crystallized mass is
3x10-12 kg/impact )
D T
1x10-7 (max 3x10-5) of
excavated ice is crystallized r
r /rp

20. Surface of 0.5 mm depth is whole crystallized in
600(y)ｘ 1/(1ｘ10-7)～ 6 ｘ 109 years
(min. 2x107 years)
UV photons and high energy particles spatters
　１ｘ10-5 (mm/y) ｘ 6ｘ109 (y)= 6 ｍｍ
(min. 0.2mm)
Micrometeorite bombardments cannot explain
the present existence of surface crystalline water ice.

21. 1 mm / 40 day Slow deposition creates crystalline ice. amorphous
log [deposition rate] (cm-2 s-1)
1 mm / 40 day
crystal
(Kouchi et al. 1994)

22. Accretion heating (quick accretion)
Total accretion energy Eacc
Eacc/M ~ 3/5 [GM / R]
Specific heat C = 1.5x103 J K-1 kg-1
C DTacc = Eacc / M
DTacc = 6 K
Not enough

23. Giant impact Impact heating ΔT ＝ ５０～１５０ K
depends on the impact parameter
Canup 2005

24. Summary
The surface of the satellite can be explained by almost pure crystalline water ice.
Amorphized layer is quickly removed by spattering
Crystallization by Micrometeorite bombardments cannot explain the present existence of crystalline water ice.
(……need more knowledge on KBO environment)
Accretion heating is not enough to crystallize the satellite.

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