Crystalline water ice on the satellite of 2003 EL61 2006.07.07 (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)

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

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

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)

(~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

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

primary satellite Satellite + sky sky Primary Satellite

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

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

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.

Amorphization by UV photon （Kouchi & Kuroda 1990) one hour exposure of UV flux ~1014 photon/cm2 s (l=110-400 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

Strazzula et al. 2003

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 s @ 43 AU ~ 10-6 mm/year

Westley et al. 1995

Shi et al. 1995

Gardening by micrometeorides assumption： Dust particle: Grun et al. 1993 mi　= 8 x 10-16 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

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 10-13 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

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.

Impact shock heating D T 1x10-7 (max 3x10-5) of r /rp Wada Solve Rankine-Hugoniot equation DT > 50 - 100 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

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.

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)

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

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

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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