生物谷综合：众所周知，地球上已发现的生命都是有机的，那么，宇宙中所有的生命都是有机的吗？现在谁也无法回答。不过，一个国际科学家小组的最新研究表明，星际尘埃中的无机物质有可能形成一种类似生命基础的螺旋结构。这一发现暗示着地球之外的生命或许并不需要有机分子作为基本材料，同时也为地球上生命起源提出了一种新的可能的解释。相关论文发表在8月9日的《新物理学杂志》（New Journal of Physics）上。
这听起来确实有些天方夜谭。不过，俄罗斯科学院普通物理研究所（General Physics Institute）的V.N. Tsytovich和德国马普地外物理研究所（Max-Planck Institute for Extraterrestrial Physics）以及澳大利亚悉尼大学的科学家通过研究等离子体中的复杂的无机原料混合物发现，只要有合适的条件，无机粒子能够变成有组织的螺旋结构。而且，这些螺旋结构之间会以与有机物质和生命相关联的方式发生相互作用。
到目前为止，物理学家认为，等离子体中的粒子之间几乎没有组织性可言。不过，Tsytovich和同事利用分子动力学计算机模型证明，随着电荷逐渐分离和等离子体变得极化，上述的自组装过程是有可能发生的。研究人员认为，这些由固体粒子所形成的螺旋结构自身都带有电荷，因而彼此间会相互吸引。
更不可思议的是，研究人员表示，这些螺旋结构还会经历一些通常与生物分子（如DNA和蛋白质）相关的变化。比如，这些螺旋结构会断开、分叉，进而形成两个原始结构的副本。此外，这些螺旋结构间的相互作用还会促使它们中的不稳定结构分解，进化成更多的稳定结构留存于等离子体中。
Tsytovich说，“这些复杂的等离子体结构所表现出的自治、复制和进化的性质，使它们满足了一种无机生命候选物质的所有必需条件。”
研究人员表示，形成螺旋结构等离子体条件在外太空广泛存在。即使是在地球上，雷击也会产生等离子体。因此，有可能原始地球上最先出现的是无机生命形式，而有机分子以它们作为模板，演化成为今天的样子。（科学网 任霄鹏/编译）
原始出处:
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: tsyto@mpe.mpg.de, tsytov@td.lpi.ac.ru, gem@mpe.mpg.de, konopka@mpe.mpg.de and thomas@mpe.mpg.de
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
