有一個額外行星的海王星遷徙模型

Neptune migration model with one extra planet

葉倫文(Lun-Wen Yeh)

指導教授 ： 張祥光

國立清華大學/理學院/物理學系/博士(2009年)

https://doi.org/10.6843/NTHU.2009.00447

摘要

摘要
我們研究在傳統的海王星遷徙模型(Neptune migration model)裡多加一個0.1到2.0M⊕的額外行星。在行星遷徙的時期裡，這個額外行星處於海王星的3:2平均運動共振(mean motion resonance)，接著在類木行星(Jovian planet)遷徙到接近現在軌道時，它會脫離古柏帶(Kuiper belt)。在傳統的海王星遷徙模型裡多加這個額外行星，且假設原始盤面只延伸到45 AU，可以解釋一些傳統的海王星遷徙模型不能解釋的觀測現象。(1)可以產生大傾角的類冥小天體(Plutino)，i ≈15-350。(2)讓傳統古柏帶天體 (Classical Kuiper belt object)有比較大的離心率和傾角。(3)讓海王星的3:2和2:1共振天體的個數比例變大，且讓海王星的3:2共振天體和傳統古柏帶天體的個數比例變小，可較符合觀測。(4)最後，可以產生海王星5:2共振天體。然而從數值模型的結果顯示，這個模型是一個發生機率低的事件。另外，有兩項模擬的結果可能和觀測不符合。第一項是在傳統古柏帶裡小傾角天體的數量不足，第二項是在a ≈50-52 AU處，有小傾角且接近圓軌道的天體產生。根據我們目前的研究，在傳統的海王星遷徙模型裡照我們的方式多加一個額外的行星可能不太合適，因為以上兩個原因和發生的機率可能很低。機率低和小傾角天體的不足這兩個問題，可以考慮用更實際的模型去研究。

關鍵字

古柏帶 ； 共振 ； 海王星

並列摘要

Abstract
We explore conventional Neptune migration model with one additional planet of mass at 0.1-2.0 M⊕ (Yeh and Chang, 2009). This planet inhabited in the 3:2 mean motion resonance with Neptune during planet migration epoch, and then escaped from the Kuiper belt when Jovian planets parked near the present orbits. Adding this extra planet and assuming the primordial disk truncated at about 45 AU in the conventional Neptune migration model, it is able to explain the complex structure of the observed Kuiper belt better than the usual Neptune migration model did in several respects, which are the following. (1) High-inclination Plutinos with i ≃ 15°-35° are produced. (2)generating the excitation of the classical Kuiper belt objects, which have moderate eccentricities and inclinations. (3) Producing the larger ratio of Neptune's 3:2 to 2:1 resonant particles, and the lower ratio of particles in the 3:2 resonance to those in the classical belt, which may be more consistent with observations. (4)Finally, several Neptune’s 5:2 resonant particles are obtained. However, numerical experiments imply that this model is a low-probability event. In addition to the low probability, two features produced by this model may be inconsistent with the observations. They are small number of low-inclination particles in the classical belt, and the production of a remnant population with near-circular and low-inclination orbit within a ≃ 50-52 AU. According to our present study, including one extra planet in the conventional Neptune migration model as the scenario we explored here may be unsuitable because of the low probability, and the two drawbacks mentioned above, although this model can explain better several features which are hard to produce by the conventional Neptune migration model. The issues of low-probability event and the lack of low-inclination Kuiper belt objects in the classical belt are interesting and may be studied further under a more realistic consideration.

並列關鍵字

Kuiper belt ； resonance ； Neptune

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