Rogerio Deienno, David Nesvorný, Matthew S. Clement, William F. Bottke, André Izidoro, Kevin J. Walsh
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In this work, we numerically simulate the accretion of objects in the MAB region during the time when gas in the protoplanetary disk still existed while assuming different MAB primordial masses. We then account for the depletion of that population happening after gas disk dispersal. In our analysis, we subdivided the MAB into five subregions and showed that the depletion factor varies throughout the MAB. This results in uneven radial- and size-dependent depletion of the MAB. We show that the MAB primordial mass has to be ≲2.14 × 10<sup>−3</sup>\n<italic toggle=\"yes\">M</italic>\n<sub>⊕</sub>. Larger primordial masses would lead to the accretion of tens to thousands of S-complex objects with <italic toggle=\"yes\">D</italic> > 500 km in the MAB. Such large objects would survive depletion even in the outer subregions (<italic toggle=\"yes\">a</italic> > 2.5 au), thus being inconsistent with observations. 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The former probably originated from the inner solar system (interior to Jupiter’s orbit), while the latter probably originated from the outer solar system. Following this definition, (4) Vesta, a V-type residing in the inner MAB (<italic toggle=\\\"yes\\\">a</italic> < 2.5 au), is the sole <italic toggle=\\\"yes\\\">D</italic> > 500 km object akin to the S-complex that potentially formed in situ. This provides a useful constraint on the number of <italic toggle=\\\"yes\\\">D</italic> > 500 km bodies that could have formed, or grown, within the primordial MAB. In this work, we numerically simulate the accretion of objects in the MAB region during the time when gas in the protoplanetary disk still existed while assuming different MAB primordial masses. We then account for the depletion of that population happening after gas disk dispersal. In our analysis, we subdivided the MAB into five subregions and showed that the depletion factor varies throughout the MAB. 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引用次数: 0
摘要
众所周知,主小行星带(MAB)主要由两个不同分类学类别的天体组成,这里一般定义为S-和C-复合天体。前者可能来自内太阳系(木星轨道内部),后者可能来自外太阳系。根据这一定义,(4) 灶神星,一个位于内MAB(a < 2.5 au)的V型天体,是唯一一个可能在原地形成的类似于S型复合天体的D > 500 km天体。这为原始 MAB 中可能形成或生长的 D > 500 公里天体的数量提供了一个有用的约束。在这项工作中,我们用数值模拟了在原行星盘中气体仍然存在的时期,MAB区域内的天体吸积情况,同时假设了不同的MAB原始质量。然后,我们对气体盘散开后发生的种群耗竭进行了核算。在分析中,我们将人与生物圈细分为五个子区域,结果表明整个人与生物圈的损耗因子是不同的。这导致了 MAB 不均匀的径向损耗和尺寸损耗。我们表明,人与生物圈的原始质量必须是 ≲2.14 × 10-3M⊕。更大的原始质量将导致数以万计的S-复合天体在MAB中增生,其D > 500公里。这样大的天体即使在外层子区域(a > 2.5 au)也能存活下来,因此与观测结果不符。我们的研究结果还表明,包括(4)灶神星在内的D > 200-300千米的S-复合天体很可能是植入人与生物圈的陆地行星,而不是在原地形成的。
Accretion and Uneven Depletion of the Main Asteroid Belt
The main asteroid belt (MAB) is known to be primarily composed of objects from two distinct taxonomic classes, generically defined here as S- and C-complex. The former probably originated from the inner solar system (interior to Jupiter’s orbit), while the latter probably originated from the outer solar system. Following this definition, (4) Vesta, a V-type residing in the inner MAB (a < 2.5 au), is the sole D > 500 km object akin to the S-complex that potentially formed in situ. This provides a useful constraint on the number of D > 500 km bodies that could have formed, or grown, within the primordial MAB. In this work, we numerically simulate the accretion of objects in the MAB region during the time when gas in the protoplanetary disk still existed while assuming different MAB primordial masses. We then account for the depletion of that population happening after gas disk dispersal. In our analysis, we subdivided the MAB into five subregions and showed that the depletion factor varies throughout the MAB. This results in uneven radial- and size-dependent depletion of the MAB. We show that the MAB primordial mass has to be ≲2.14 × 10−3M⊕. Larger primordial masses would lead to the accretion of tens to thousands of S-complex objects with D > 500 km in the MAB. Such large objects would survive depletion even in the outer subregions (a > 2.5 au), thus being inconsistent with observations. Our results also indicate that S-complex objects with D > 200–300 km, including (4) Vesta, are likely to be terrestrial planetesimals implanted into the MAB rather than formed in situ.