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NHK カルチャー講義(第2回)

NHK カルチャー講義(第2回)

NHK カルチャー講義「惑星科学最前線 ~太陽系誕生の謎~」の第2回目の講義資料です。

Takanori Sasaki

March 08, 2016
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  1. ଠཅܥͷىݯϞσϧ ఱಈઆ͔Β஍ಈઆ΁ ɾ/FXUPO  ɿʮϓϦϯΩϐΞʯ ੈلҎલ ɾ,BOU  -BQMBDF 

    ɿ੕Ӣઆ ੈلҎ߱ ɾ4BGSPOPW  ɿίΞूੵϞσϧ ɾ$BNFSPO  ɿॏྗෆ҆ఆϞσϧ ɾ)BZBTIJFUBM  ɿίΞूੵϞσϧ
  2. ݪ࢝ଠཅܥԁ൫ͷ̎ͭͷϞσϧ         

       ©Newton Press ژ౎ϞσϧʢྛϞσϧʣ ΩϟϝϩϯϞσϧ ஍ٿܕ࿭੕ɾڊେΨε࿭੕ɾڊେණ࿭੕ͷ࡞Γ෼͚ ɹˠଠཅܥܗ੒ʹؔͯ͠͸ɺژ౎Ϟσϧͷํʹ܉഑ (c) Alan P. Boss
  3. ݪ࢝࿭੕ܥԁ൫ '"('+, !  !+% ) ( !+*& '+ ! ) $

    #) ('+ ݪ࢝࿭੕ܥԁ൫ ෼ࢠӢίΞ ෼ࢠӢίΞͷऩॖ ɹॏྗͱԕ৺ྗͷͭΓ͍͋ ݪ࢝࿭੕ܥԁ൫͕ܗ੒ (c) NASA
  4. ඍ࿭੕ܗ੒γφϦΦͱ༷ʑͳࠔ೉ μετ(≲µm) ࿭੕(≳103km) ݪ࢝࿭੕ܥԁ൫ ඍ࿭੕(≳km) ࿭੕ܗ੒ͱඍ࿭੕ܗ੒ !5 ice +rock ice+rock

    rock Itokawa (~0.5km) rock ॏྗूੵ ෼ࢠؒྗूੵ + μετ૚ͷࣗݾ ॏྗෆ҆ఆ? εϊʔϥΠϯ (~1-3AU?) ௚઀߹ମ੒௕ μετͷࣗݾॏྗෆ҆ఆ μετ ඍ࿭੕ ЖN NN N LN ੩ి൓ൃোน ௓ͶฦΓোน த৺੕མԼোน িಥഁյোน ཚྲྀোน ☓☓ ☓ ☓☓
  5.  !10-4 # " $    [g/cm3] roll

    imp 2 3 ~ 40 . 2 ~ E E N dN d f f      E imp = - p dV  V 0 V Suyama et al. submitted to ApJ    μετͷ߹ମ੒௕ μετͷ߹ମ੒௕ ɹˠඍ࿭੕ܗ੒ ඍ࿭੕ͷԁ൫͕ܗ੒ (c) Toru Sayama ණඍ࿭੕͸ܗ੒Մೳ ؠੴඍ࿭੕͸ഁյ͕ ୎ӽ͠ܗ੒ෆՄೳ
  6. KOKUBO AND IDA FIG. 4. Time evolution of the maximum

    mass (solid curve) and the mean mass (dashed curve) of the system. thanthisrangearenotstatisticallyvalidsinceeachmassbinoften has only a few bodies. First, the distribution tends to relax to a ๫૸త੒௕ͷ༷ࢠ ฏۉ஋ ࠷େͷఱମ ඍ࿭੕ͷ๫૸త੒௕ ɹˠݪ࢝࿭੕͕஀ੜ͢Δ 20 KOKUBO AND IDA FIG. 3. Snapshots of a planetesimal system on the a–e plane. The circles represent planetesimals and their radii are proportional to the radii of planetesi- mals. The system initially consists of 3000 equal-mass (1023 g) planetesimals. FIG. 4. Time evolution of the maximum mass (solid curve) and the mean mass (dashed curve) of the system. thanthisrangearenotstatisticallyvalidsinceeachmassbinoften has only a few bodies. First, the distribution tends to relax to a decreasing function of mass through dynamical friction among (energy equipartition of) bodies (t = 50,000, 100,000 years). Second, the distributions tend to flatten (t = 200,000 years). This is because as a runaway body grows, the system is mainly heated by the runaway body (Ida and Makino 1993). In this case, the eccentricity and inclination of planetesimals are scaled by the يಓ௕൒ܘ<"6> يಓ཭৺཰ ࣭ྔ<H> ࣌ؒ<೥> <,PLVCP*EB >
  7. Չ઎త੒௕ͷ༷ࢠ FORMATION OF PROTOPLANETS FROM PLANETESIMALS 23 FIG. 7. Snapshots

    of a planetesimal system on the a–e plane. The cir- cles represent planetesimals and their radii are proportional to the radii of planetesimals. The system initially consists of 4000 planetesimals whose to- tal mass is 1.3 × 1027 g. The initial mass distribution is given by the power- FIG. 8. The number of bodies in linear mass bins is plotted for t = 100,000, 200,000, 300,000, 400,000, and 500,000 years. In Fig. 10, we plot the maximum mass and the mean mass of يಓ཭৺཰ ֤৔ॴͰඍ࿭੕͕๫૸త੒௕ ɹˠ౳αΠζͷݪ࢝࿭੕͕ฒͿ Չ઎త੒௕ͱΑͿ ʹ ֤يಓͰͷݪ࢝࿭੕ ࣭ྔ [kg] ܗ੒࣌ؒ [yr] ஍ٿيಓ 1×1024 7×105 ໦੕يಓ 3×1025 4×107 ఱԦ੕يಓ 8×1025 2×109 يಓ௕൒ܘ<"6> <,PLVCP*EB >
  8. ݪ࢝࿭੕͔Β࿭੕΁ )-/    2  .3 ( )

    -/(% -/ ) 0  #    " 4+ ݪ࢝࿭੕ͷ࣭ྔ<஍ٿ࣭ྔ> يಓ௕൒ܘ<"6> ஍ٿܕ࿭੕ ɹݪ࢝࿭੕ಉ࢜ͷ߹ମ ڊେΨε࿭੕ ɹݪ࢝࿭੕ͷΨεั֫ ڊେණ࿭੕ ɹݪ࢝࿭੕ͦͷ·· TOPXMJOF (c) Eiichiro Kokubo
  9. δϟΠΞϯτΠϯύΫτ يಓ௕൒ܘ<"6> يಓ཭৺཰ planets is hnM i ’ 2:0 Æ

    0:6, which means that the typical result- ing system consists of two Earth-sized planets and a smaller planet. In this model, we obtain hna i ’ 1:8 Æ 0:7. In other words, one or two planets tend to form outside the initial distribution of protoplanets. In most runs, these planets are smaller scattered planets. Thus we obtain a high efficiency of h fa i ¼ 0:79 Æ 0:15. The accretion timescale is hTacc i ¼ 1:05 Æ 0:58 ð Þ ; 108 yr. These results are consistent with Agnor et al. (1999), whose initial con- Fig. 2.—Snapshots of the system on the a-e (left) and a-i (right) planes at t ¼ 0, 1 are proportional to the physical sizes of the planets. KOKUBO, KOMIN 1134 ௕͍࣌ؒΛ͔͚ͯݪ࢝࿭੕ಉ࢜ͷيಓ͕ཚΕΔ ɹˠޓ͍ʹিಥɾ߹ମͯ͠ΑΓେ͖ͳఱମʹ੒௕ <,PLVCP*EB > (c) Hidenori Genda
  10. ݄ͷىݯઆ ั֫આ ෼྾આ ૒ࢠઆ ݪ࢝஍ٿ͕ߴ଎ճసʹΑΓ;͘ΒΈ  ͦͷҰ෦͕ͪ͗Ε݄͕ͯ஀ੜ ஍ٿيಓ෇ۙͰͷඍ࿭੕ͷूੵʹΑΓ  ஍ٿͱ͸ಠཱʹ݄͕ܗ੒

    ஍ٿͱ͸ผͷ৔ॴͰ࡞ΒΕ݄͕ͨ  ஍ٿͷۙ͘Λ௨ͬͨͱ͖ʹัΒ͑ΒΕͨ ߴ଎ճస͕೉͍֯͠ӡಈྔ͕େ͖͗͢Δ ݄ͷ಺෦ߏ଄͕આ໌Ͱ͖ͳ͍݄Λ࢒ͤͳ͍ ั֫֬཰͕௿͍Խֶత੍໿Λຬͨͤͳ͍
  11. ڊେΨε࿭੕ͷܗ੒ͷ༷ࢠ Fig. 4.—Structure around the Hill sphere for model M04

    on the midplane (left) and in three dimensions, shown in bird’s-eye view (right). The gas stream MACHIDA ET AL. 1226 V 1.—Time sequence for model M04. The density (color scale) and velocity distributions (arrows) on the cross section in the ˜ z ¼ 0 plane are plotted. The bottom ¼ 3) are 4 times the spatial magnification of the top panels (l ¼ 1). Three levels of grids are shown in each top (l ¼ 1, 2, and 3) and bottom (l ¼ 3, 4, and 5) panel. l of the outermost grid is denoted in the top left corner of each panel. The elapsed time ˜ tp and the central density ˜ c on the midplane are denoted above each of the ls. The velocity scale in units of the sound speed is denoted below each panel. पғͷԁ൫Ψε͕ݪ࢝࿭੕ͷॏྗݍ಺ʹั֫͞ΕΔ (c) Takayuki Tanigawa
  12. 5ZQF*NJHSBUJPOͷΧΦεੑ © F. Maseet ԁ൫ͱͷॏྗ૬ޓ࡞༻ʹΑΔ࿭੕يಓҠಈ ʔ ࠞಱ ৽ͨͳ෺ཧɿ࿭੕يಓҠಈ ԁ൫Թ౓ޯ഑ɺྲྀମૉย೤༌ૹɺ ཚྲྀ֦ࢄ౳Λߟྀ͢Δ

    ɹˠҠಈํ޲͕มΘΔʢͨͩ͠ߴ଎ʣ ɹɹɹɹɹ<1BBSEFLPPQFSFUBM  > ཚྲྀʹΑΔີ౓ΏΒ͔͗Βͷॏྗઁಈ ɹˠϥϯμϜӡಈΛҾ͖ى͜͢ ɹ<*EBFUBM  0LV[VNJ0SNFM B C> ͍ͣΕʹͯ͠΋࿭੕͸ԁ൫Ψεͱͷ૬ޓ࡞༻Ͱಈ͖ճΔ
  13. .JHSBUJPO5SBQ Possible%migra3on%trap:%type%I%% ! %adiaba3c%+%isothermal%disk% ,,,,,e.g.,,Paardekooper,&,Papalouzou,(2009),,Paardekooper,et,al.,(2010,,11), ,,,,,,,,,,,,,,,,Kretke,&,Lin,(2012), ! %gas%density%jump% adiabatic isothermal “saturation” of

    corotation torque: delicate 0.1AU 1AU 10AU dead zone (DZ) inner disk edge or DZ inner edge Masset,et,al.,(2006), Ogihara,et,al.,(2010) DZ outer edge Hasegawa,&,Pudritz,(2012), Regaly,et,al.,(2013) ice line Kretke,&,Lin,(2007) theory: not clear <*EBTBO`TUBML>
  14. l-PDBMz1MBOFU'PSNBUJPO.PEFM Solar%system:%“local”%forma3on??% ! %I1995,:,uniform,disk,w/o,orbital,migraDon, ! ,1995I,:,uniform,disk,with,orbital,migraDon, ! ,New,idea:,nonIuniform,disk, ,,,,,,,,,,,,,,,,,,,,,,,start,from,2,narrow,disk,regions??, ,,,,,,,,,,,,,,,,,,,,,,,,migraDon,trap?,, ,,,,,,,,,,,,,,,,,,,,,,,,,,,,‘Grand,Tack’,model?,(Walsh+,2011), 0.1AU 1AU

    10AU .F7&.B+46/ close%scaLering% &%giant%impacts% ,,Morishima+,(2008), ,,Hansen,(2009),, induced%forma3on%of%Saturn% ,,Kobayashi,,Ormel,,Ida,(2012)% diffusion%via%planetesimal%scaLering% ,,Fernandez,&,Ip,(1994), secular%perturba3on%by%JS%in%2:1% ,,Nice,model,, ~2M ⊕  50I100M ⊕  <*EBTBO`TUBML> lͪΌΜͱͨ͠࿦จ͸ग़͍ͯͳ͍͕ଟ͘ͷਓ͕Կͱͳ͘ࢥ͍ͬͯΔz <4BTBLJFUBM JOQSFQ>