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NHK カルチャー講座「惑星科学最前線〜太陽系誕生のシナリオを描き出す〜」(第一回)

NHK カルチャー講座「惑星科学最前線〜太陽系誕生のシナリオを描き出す〜」(第一回)

NHK カルチャー梅田教室にて、惑星形成論に関する講座を行ってきました。そのときに用いた講演資料です。

Takanori Sasaki

May 13, 2018
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  1. ࣗݾ঺հ ⿣ ࠤʑ໦وڭʢ͖͔ͨ͞͞ͷΓʣ ⿣ ژ౎େֶɹେֶӃཧֶݚڀՊɹ෺ཧֶɾӉ஦෺ཧֶઐ߈
 Ӊ஦෺ཧֶڭࣨɹॿڭ ⿣ ೥݄ʹ౦ژେֶͰֶҐΛऔಘ ⿣ ઐ໳͸l࿭੕ͷܗ੒ͱਐԽzͷཧ࿦ݚڀ


    ɹ࿭੕ܥ͸ͲͷΑ͏ʹͯ͠࡞ΒΕΔͷ͔
 ɹ࿭੕ܥ͸ͲͷΑ͏ʹਐԽ͍ͯ͘͠ͷ͔
 ɹ զʑ͸Կॲ͔ΒདྷͯԿॲ΁ߦ͘ͷ͔ʁ ੜ໋Λ॓͢lୈೋͷ஍ٿz͸ଘࡏ͢Δ͔ʁ (c) NASA
  2. ଠཅܥͷߏ੒ϝϯόʔ ஍ٿܕ࿭੕ ɹɹਫ੕ ɹɹۚ੕ ɹɹ஍ٿ ɹɹՐ੕ ڊେΨε࿭੕ ɹɹɹ໦੕ ɹɹɹ౔੕ ڊେණ࿭੕

    ɹɹఱԦ੕ ɹɹւԦ੕ খఱମʢখ࿭੕ ଠཅܥ֎ԑఱମ ΦʔϧτͷӢʣ (c) ikachi.org
  3. ਫ੕ ۚ੕ ஍ٿ Ր੕ يಓ௕൒ܘ [AU] 0.39 0.72 1 1.52

    ެసपظ [೥] 0.241 0.615 1 1.881 ࣭ྔ [஍ٿ = 1] 0.055 0.82 1 0.11 ൒ܘ [km] 2440 6052 6378 3396 ີ౓ [kg/m3] 5430 5240 5520 3930 Ӵ੕ͷ਺ 0 0 1 2 ஍ٿܕ࿭੕ͷੑ࣭
  4. ໦੕ ౔੕ ఱԦ੕ ւԦ੕ يಓ௕൒ܘ [AU] 5.2 9.6 19.2 30.1

    ެసपظ [೥] 11.86 29.46 84.02 164.7 ࣭ྔ [஍ٿ = 1] 317.8 95.2 14.5 17.2 ൒ܘ [km] 71490 60270 25560 24760 ີ౓ [kg/m3] 1330 690 1270 1640 Ӵ੕ͷ਺ 49 53 27 13 ڊେΨε࿭੕ɾණ࿭੕ͷੑ࣭
  5. ଠཅܥܗ੒ʹؔ͢Δ̎ͭͷϞσϧ         

       ©Newton Press ژ౎ϞσϧʢྛϞσϧʣ ΩϟϝϩϯϞσϧ ஍ٿܕ࿭੕ɾڊେΨε࿭੕ɾڊେණ࿭੕ͷ࡞Γ෼͚ ɹˠଠཅܥܗ੒ʹؔͯ͠͸ɺژ౎Ϟσϧͷํʹ܉഑ (c) Alan P. Boss
  6. 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 ☓☓ ☓ ☓☓
  7. 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 >
  8. 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 >
  9. 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
  10. 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
  11. 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 த৺੕མԼোน ☓