Takanori Sasaki
April 27, 2016
240

宇宙科学入門（2016年度前期）

April 27, 2016

Transcript

2. ຊ೔ͷ಺༰ ✤ ଠཅܥܗ੒࿦ͷ؆୯ͳϨϏϡʔ  ɹඪ४ཧ࿦ʢژ౎Ϟσϧʣͷ֓ཁͱͦͷ֦ு ✤ ܥ֎࿭੕ͷൃݟɺͦͯ͠൚࿭੕ܗ੒ཧ࿦΁  ɹଟ༷ͳ࿭੕ܥΛ͍͔ʹ࡞Δ͔ ✤ Ӊ஦ʹ͋;ΕΔ ”ϋϏλϒϧϓϥωοτ”

ͨͪ  ɹզʑ͸Ͳ͔͜ΒདྷͯɺͲ͜΁ߦ͘ͷ͔

4. ଠཅܥͷߏ੒ϝϯόʔ ஍ٿܕ࿭੕ ɹɹਫ੕ ɹɹۚ੕ ɹɹ஍ٿ ɹɹՐ੕ ڊେΨε࿭੕ ɹɹɹ໦੕ ɹɹɹ౔੕ ڊେණ࿭੕

ɹɹఱԦ੕ ɹɹւԦ੕ (c) ikachi.org
5. ଠཅܥܗ੒ඪ४ཧ࿦ʢژ౎Ϟσϧʣ         

   ©Newton Press 巨大氷惑星形成

>
7. ݪ࢝࿭੕ܥԁ൫ '"('+, !  !+% ) ( !+*& '+ ! ) \$

#) ('+ ݪ࢝࿭੕ܥԁ൫ ෼ࢠӢίΞ ෼ࢠӢίΞͷऩॖ ɹॏྗͱԕ৺ྗͷͭΓ͍͋ ݪ࢝࿭੕ܥԁ൫͕ܗ੒ (c) NASA

10. ඍ࿭੕ͷ߹ମ੒௕ ਺LNαΠζͷ ඍ࿭੕͕ܗ੒ ޓ͍ʹিಥɾ߹ମ Λ܁Γฦ͠੒௕ ˣ ๫૸త੒௕ ɹେཻ͖͍ࢠ΄Ͳ੒௕͕଎͍ டংత੒௕ ɹશͯͷཻࢠ͕ಉ͡଎౓Ͱ੒௕

(c) Kouji KANBA

12. 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੒௕ ɹˠݪ࢝࿭੕͕஀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 >
13. 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 >
14. ݪ࢝࿭੕͔Β࿭੕΁ )-/    2  .3 ( )

-/(% -/ ) 0  #    " 4+ ݪ࢝࿭੕ͷ࣭ྔ<஍ٿ࣭ྔ> يಓ௕൒ܘ<"6> ஍ٿܕ࿭੕ ɹݪ࢝࿭੕ಉ࢜ͷ߹ମ ڊେΨε࿭੕ ɹݪ࢝࿭੕ͷΨεั֫ ڊେණ࿭੕ ɹݪ࢝࿭੕ͦͷ·· TOPXMJOF (c) Eiichiro Kokubo
15. 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 ɹˠޓ͍ʹিಥɾ߹ମͯ͠ΑΓେ͖ͳఱମʹ੒௕ <,PLVCP*EB > (c) Hidenori Genda
16. ڊେఱମিಥʹΑΔԁ൫ܗ੒ ݪ࢝஍ٿʹՐ੕αΠζͷ ݪ࢝࿭੕͕িಥ ඈͼࢄͬͨഁย͕஍ٿͷ पғʹԁ൫Λܗ੒ (c) Robin Canup [Canap &

Asphaug, 2001]

Wikipedia
21. ଠཅܥܗ੒ඪ४ཧ࿦ʢژ౎Ϟσϧʣ         

   ©Newton Press 巨大氷惑星形成

Michel Mayor

27. ଟ༷ͳݪ࢝࿭੕ܥԁ൫ Դڇ࠲ ΁ͼ͔͍ͭ࠲      ԁ൫ͷ࣭ྔ<ଠཅ࣭ྔ> ൃ

ݟ ਺ ଠཅܥ෮ݩԁ൫ Ӊ஦ʹ͸༷ʑͳ࣭ྔΛ࣋ͭݪ࢝࿭੕ܥԁ൫͕ଘࡏ ɹˠԁ൫ͷ࣭ྔͷҧ͍͕ଟ༷ͳ࿭੕ܥΛੜΈग़͢ʂʁ
28. ଟ༷ͳԁ൫͔Βੜ·ΕΔଟ༷ͳ࿭੕ ԁ൫ͷ࣭ྔͷҧ͍ˠΨε࿭੕ͷ਺ͱҐஔͷҧ͍ the escape velocity of protoplanets. This high random

veloc- ity makes the accretion process slow and ineﬃcient and thus Tgrow longer. This accretion ineﬃciency is a severe problem On the ot in circular o HD 192263 with Æ1e 1 for in situ f case. It is d slingshot m circular orb the magnet may be wea disks may b Terrestria Jovian plan planetary a key process systems. We conﬁr holds in Æsolid ¼ Æ1 ð ¼ 1=2; 3= tions. We d systems dep disk proﬁle growth tim and (17), re a Mdisk T <T grow disk T <T cont disk Fig. 13.—Schematic illustration of the diversity of planetary systems against the initial disk mass for < 2. The left large circles stand for central stars. The double circles (cores with envelopes) are Jovian planets, and the others are terrestrial and Uranian planets. [See the electronic edition of the Journal for a color version of this ﬁgure.] ݪ࢝࿭੕ܥԁ൫ͷ࣭ྔ يಓ௕൒ܘ த৺੕͔Βͷڑ཭ <,PLVCP*EB >
29. ࿭੕ͷҠಈʹ൐͏࿭੕ܥͷมԽ earing continues through scattering. After 00 million years the

inner disk is composed the collection of planetesimals at 0.06 AU, a M] planet at 0.12 AU, the hot Jupiter at 0.21 U, and a 3 M] planet at 0.91 AU. Previous sults have shown that these planets are likely be stable for billion-year time scales (15). Many bodies remain in the outer disk, and ac- orbital time scales and high inclinations. Two of the four simulations from Fig. 2 contain a 90.3 M] planet on a low-eccentricity orbit in the habitable zone, where the temper- ature is adequate for water to exist as liquid on a planet_s surface (23). We adopt 0.3 M] as a lower limit for habitability, including long-term climate stabilization via plate tectonics (24). three categories: (i) hot Earth analogs interior to the giant planet; (ii) Bnormal[ terrestrial planets between the giant planet and 2.5 AU; and (iii) outer planets beyond 2.5 AU, whose accretion has not completed by the end of the simulation. Properties of simulated planets are segregated (Table 1): hot Earths have very low eccentric- ities and inclinations and high masses because g. 1. Snapshots in time of the evolution of one simulation. Each panel ots the orbital eccentricity versus semimajor axis for each surviving body. he size of each body is proportional to its physical size (except for the ant planet, shown in black). The vertical ‘‘error bars’’ represent the sine of each body’s inclination on the y-axis scale. The color of each dot corresponds to its water content (as per the color bar), and the dark inner dot represents the relative size of its iron core. For scale, the Earth’s water content is roughly 10j3 (28). λΠϓ* **࿭੕མԼʹ ΑΓ࿭੕ܥͷيಓ͕େ͖ ͔͖͘ཚ͞ΕΔ they accrete on the migration time scale (105 years), so there is a large amount of damping during their formation. These planets are remi- niscent of the recently discovered, close-in 7.5 M] planet around GJ 876 (25), whose formation is also attributed to migrating resonances (26). ଟ༷ͳ࿭੕ܥܗ੒ <3BZNPOEFUBM >
30. Weidenschilling &,Marzari (1996),,Lin,&   a GM a GM a

GM a GM a GM * * 3 * 2 * 1 *     \$&,60 45 '"#, (t >~ 1My) /% , "# 2-+0'! 3. *) 1."#3. 00 a1 0  . 00 a1(. final e يಓෆ҆ఆʹΑΔ࿭੕ܥͷมԽ ࿭੕ؒͷॏྗͷӨڹ͕ ੵΈॏͳͬͯ࠷ऴతʹ ޓ͍ͷيಓ͕ෆ҆ఆԽ ҟͳΔ࿭੕ܥ΁ ˣ &DDFOUSJD1MBOFUͷىݯʁ </BHBTBXBFUBM >