Comet formation in collapsing pebble clouds. What cometary bulk density implies for the cloud mass and dust-to-ice ratio
Comet formation in collapsing pebble clouds. What cometary bulk density implies for the cloud mass and dust-to-ice ratio
复制标题
塌陷的卵石云中彗星的形成。
DOI：
10.1051/0004-6361/201526565
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发表时间：
2016
影响因子：
6.5
通讯作者：
J. Blum
中科院分区：
文献类型：
--
作者：
S. Lorek;B. Gundlach;P. Lacerda;J. Blum
彗星是在太阳星云的冰线之外形成的冰质星子的残余。然而，由于生长障碍和时间尺度的限制，从微米大小的尘埃和冰粒生长到公里大小的物体是困难的。通过流动不稳定性形成的卵石云的引力坍缩可能为彗星的形成提供了合适的机制。
我们研究了厘米大小的多孔冰/灰尘混合卵石的碰撞压缩崩溃卵石云。为此，我们开发了一个碰撞模型的鹅卵石组成的混合物的冰和灰尘，其特征在于其灰尘冰的质量比。使用最终压缩的卵石，我们约束组合的初始云质量，初始pepple孔隙度，和尘冰比，导致cometesimals这是一致的，与观察到的散装性质的彗星核。
我们发现，所观察到的高孔隙度和低密度的彗星核的~0.5克/立方厘米，只能解释，如果彗星形成的云质量约M> 1 e18克。质量较低的云只有在卵石最初非常致密的情况下才能起作用。此外，尘埃与冰的比例必须在3到9之间，才能与观测到的彗星核的整体性质相匹配。（节略本）
Comets are remnants of the icy planetesimals that formed beyond the ice line in the Solar Nebula. Growing from micrometre-sized dust and ice particles to km-sized objects is, however, difficult because of growth barriers and time scale constraints. The gravitational collapse of pebble clouds that formed through the streaming instability may provide a suitable mechanism for comet formation.
We study the collisional compression of cm-sized porous ice/dust-mixed pebbles in collapsing pebble clouds. For this, we developed a collision model for pebbles consisting of a mixture of ice and dust, characterised by their dust-to-ice mass ratio. Using the final compression of the pebbles, we constrain combinations of initial cloud mass, initial pepple porosity, and dust-to-ice ratio that lead to cometesimals which are consistent with observed bulk properties of cometary nuclei.
We find that observed high porosity and low density of ~0.5 g/cc of comet nuclei can only be explained if comets formed in clouds with mass approximately M>1e18 g. Lower mass clouds would only work if the pebbles were initially very compact. Furthermore, the dust-to-ice ratio must be in the range of between 3 and 9 to match the observed bulk properties of comet nuclei. (abridged version)