宇宙生命或許起源於無機分子

    生物谷綜合：眾所周知，地球上已發現的生命都是有機的，那麼，宇宙中所有的生命都是有機的嗎？現在誰也無法回答。不過，一個國際科學家小組的最新研究表明，星際塵埃中的無機物質有可能形成一種類似生命基礎的螺旋結構。這一發現暗示著地球之外的生命或許並不需要有機分子作為基本材料，同時也為地球上生命起源提出了一種新的可能的解釋。相關論文發表在8月9日的《新物理學雜誌》（

New  Journal  of  Physics

）上。 

   這聽起來確實有些天方夜譚。不過，俄羅斯科學院普通物理研究所（General  Physics  Institute）的V.N.  Tsytovich和德國馬普地外物理研究所（Max-Planck  Institute  for  Extraterrestrial  Physics）以及澳大利亞雪梨大學的科學家通過研究等離子體中的複雜的無機原料混合物發現，只要有合適的條件，無機粒子能夠變成有組織的螺旋結構。而且，這些螺旋結構之間會以與有機物質和生命相關聯的方式發生相互作用。 

   到目前為止，物理學家認為，等離子體中的粒子之間幾乎沒有組織性可言。不過，Tsytovich和同事利用分子動力學計算機模型證明，隨著電荷逐漸分離和等離子體變得極化，上述的自組裝過程是有可能發生的。研究人員認為，這些由固體粒子所形成的螺旋結構自身都帶有電荷，因而彼此間會相互吸引。 

   更不可思議的是，研究人員表示，這些螺旋結構還會經歷一些通常與生物分子（如DNA和蛋白質）相關的變化。比如，這些螺旋結構會斷開、分叉，進而形成兩個原始結構的副本。此外，這些螺旋結構間的相互作用還會促使它們中的不穩定結構分解，進化成更多的穩定結構留存於等離子體中。 

   Tsytovich說，「這些複雜的等離子體結構所表現出的自治、複製和進化的性質，使它們滿足了一種無機生命候選物質的所有必需條件。」 

    研究人員表示，形成螺旋結構等離子體條件在外太空廣泛存在。即使是在地球上，雷擊也會產生等離子體。因此，有可能原始地球上最先出現的是無機生命形式，而有機分子以它們作為模板，演化成為今天的樣子。（科學網  任霄鵬/編譯）

原始出處:

New  Journal  of  Physics

Collision-dominated dust sheaths and voids - observations in micro-gravity experiments and numerical investigation of the force balance relations

V N Tsytovich et al 2003 New J. Phys. 5 66   doi:10.1088/1367-2630/5/1/366

V N Tsytovich1, G Morfill2, U Konopka2 and H Thomas2
1 General Physics Institute, Russian Academy of Science Moscow, Vavilova Street 38, 117942, Moscow, Russia
2 Max-Planck Institute fur Extraterrestrische Physik, 85740 Garching, Postfach 1603, Germany
E-mail: [e-mail], [e-mail], [e-mail], [e-mail] and [e-mail]

Part of Focus on Complex (Dusty) Plasmas

Abstract. Numerical solutions of stationary force balance equations are used to investigate the possible dust configurations (dust structures) in complex plasmas between two floating potential plane electrodes. The distance between electrodes is assumed to be larger than the ion-neutral mean free path and the hydrodynamic description is used. It includes the known forces operating in this limit, the ionization source and the dust charge variations. The stationary balance equations are solved both in the case of the presence of one-size dust grains and for the case of a mixture of grains with two different sizes. Recent micro-gravity experiments with single-size dust grains and two-different-size dust grains show the formation of a system of dust sheaths and dust voids between the two plane electrodes. The observed configurations of dust structures depend strongly on the gas pressure and the degree of ionization used. The numerical investigations are able to show the necessary conditions for the types of structure to be created and give their size. The size of the structures observed is larger than the ion-neutral mean free path and is of the order of magnitude of that obtained numerically. The numerical investigations give details of the spatial distributions, the dust particles, the electron/ion densities, the ion drift velocity and dust charges inside and outside different dust structures. These details have not yet been investigated experimentally and can indicate directions for further experimental work to be performed. The single-dust-sheath structure with single-size dust particles surrounded by dust free regions (dust wall-voids) and floating potential electrodes is computed. Such a structure was observed recently and the computational results are in agreement with observations. It is shown that more often a dust void in the centre is observed. It is found that a dust void in the centre region between two electrodes is formed if the ionization rate is larger than the critical ionization rate and that in the presence of the floating potential walls the central void should be surrounded by two dust sheaths. The necessary condition for this dust structure to be formed is found to be that between the sheaths and the walls there are formed two other wall-void regions. The size of the central void and the distributions of the structure parameters in the two sheaths and in the three voids are computed. The qualitative features of the structure obtained in the numerical computations correspond to those observed. The distributions of the structure parameters in the case of the two dust sheaths are quite different from that for the case of a single central sheath. The possible structures between the electrodes for the case of the presence of dust particles of two different sizes are analysed numerically. It is shown that dust particles with different sizes cannot coexist in equilibrium at the same position and that the regions with different size dust particles must be separated in space. This conclusion is in agreement with most observations performed so far. It is illustrated numerically that for the case where the central void is present the dust particles of larger size form a separate dust sheath which should be located at larger distances from the centre than that for the smaller dust particles. This result also coincides qualitatively with the observations. Computations for the distributions of the parameters in the larger size dust sheath were performed both in the case where the central part is occupied by a dust sheath with smaller size dust particles and for the case where in the central part there exists a dust void surrounded by dust sheaths with smaller size dust particles. The size of the dust void between the sheaths with different size dust particles is calculated and shown to be small as compared to the sheath thickness. In the sheath with larger size dust particles the distribution of dust and plasma parameters differs qualitatively from that of the first dust sheath with smaller size dust particles. The stability of the stationary structures both with respect to excitation of dust convection cells and with respect to oscillations of dust void size is discussed.

Received 20 January 2003
Published 9 June 2003

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