# NON-CARBON LIFEFORMS?

From the archive, originally posted by: [ spectre ]

Public release date: 14-Aug-2007

Contact: Charlie Wallace
charlie [dot] wallace [at] iop [dot] org

Physicists discover inorganic dust with lifelike qualities

Could extraterrestrial life be made of corkscrew-shaped particles of
interstellar dust? Intriguing new evidence of life-like structures
that form from inorganic substances in space are revealed today in the
New Journal of Physics. The findings hint at the possibility that life
beyond earth may not necessarily use carbon-based molecules as its
building blocks. They also point to a possible new explanation for the
origin of life on earth.

Life on earth is organic. It is composed of organic molecules, which
are simply the compounds of carbon, excluding carbonates and carbon
dioxide. The idea that particles of inorganic dust may take on a life
of their own is nothing short of alien, going beyond the silicon-based
life forms favoured by some science fiction stories.

Now, an international team has discovered that under the right
conditions, particles of inorganic dust can become organised into
helical structures. These structures can then interact with each other
in ways that are usually associated with organic compounds and life
itself.

V.N. Tsytovich of the General Physics Institute, Russian Academy of
Science, in Moscow, working with colleagues there and at the Max-
Planck Institute for Extraterrestrial Physics in Garching, Germany and
the University of Sydney, Australia, has studied the behaviour of
complex mixtures of inorganic materials in a plasma. Plasma is
essentially the fourth state of matter beyond solid, liquid and gas,
in which electrons are torn from atoms leaving behind a miasma of
charged particles.

Until now, physicists assumed that there could be little organisation
in such a cloud of particles. However, Tsytovich and his colleagues
demonstrated, using a computer model of molecular dynamics, that
particles in a plasma can undergo self-organization as electronic
charges become separated and the plasma becomes polarized. This effect
results in microscopic strands of solid particles that twist into
corkscrew shapes, or helical structures. These helical strands are
themselves electronically charged and are attracted to each other.

Quite bizarrely, not only do these helical strands interact in a
counterintuitive way in which like can attract like, but they also
undergo changes that are normally associated with biological
molecules, such as DNA and proteins, say the researchers. They can,
for instance, divide, or bifurcate, to form two copies of the original
structure. These new structures can also interact to induce changes in
their neighbours and they can even evolve into yet more structures as
less stable ones break down, leaving behind only the fittest
structures in the plasma.

So, could helical clusters formed from interstellar dust be somehow
alive? “These complex, self-organized plasma structures exhibit all
the necessary properties to qualify them as candidates for inorganic
living matter,” says Tsytovich, “they are autonomous, they reproduce
and they evolve”.

He adds that the plasma conditions needed to form these helical
structures are common in outer space. However, plasmas can also form
under more down to earth conditions such as the point of a lightning
strike. The researchers hint that perhaps an inorganic form of life
emerged on the primordial earth, which then acted as the template for
the more familiar organic molecules we know today.

http://www.iop.org/EJ/article/1367-2630/9/8/263/njp7_8_263.html

New J. Phys. 9 (2007) 263
doi:10.1088/1367-2630/9/8/263
PII: S1367-2630(07)48657-8

From plasma crystals and helical structures towards inorganic living
matter

V N Tsytovich1,5, G E Morfill2, V E Fortov3, N G Gusein-Zade1, B A

1 General Physics Institute, Russian Academy of Science, Vavilova str.
38, Moscow, 119991, Russia
2 Max-Planck-Institut für Extraterrestrische Physik, 85740 Garching,
Germany
3 Insitute of Physics of Extremal State of Matter, Russian Academy of
Science, Moscow, Russia
4 School of Physics, The University of Sydney, NSW 2006, Australia

5 Author to whom any correspondence should be addressed.

E-mail: tsyto [at] mpe [dot] mpg [dot] de

Published 14 August 2007

Abstract. Complex plasmas may naturally self-organize themselves into
stable interacting helical structures that exhibit features normally
attributed to organic living matter. The self-organization is based on
non-trivial physical mechanisms of plasma interactions involving over-
screening of plasma polarization. As a result, each helical string
composed of solid microparticles is topologically and dynamically
controlled by plasma fluxes leading to particle charging and over-
screening, the latter providing attraction even among helical strings
of the same charge sign. These interacting complex structures exhibit
thermodynamic and evolutionary features thought to be peculiar only to
living matter such as bifurcations that serve as memory marks’, self-
duplication, metabolic rates in a thermodynamically open system, and
non-Hamiltonian dynamics. We examine the salient features of this new
complex state of soft matter’ in light of the autonomy, evolution,
progenity and autopoiesis principles used to define life. It is
concluded that complex self-organized plasma structures exhibit all
the necessary properties to qualify them as candidates for inorganic
living matter that may exist in space provided certain conditions
allow them to evolve naturally.

Contents

* 1. Introduction
* 2. Plasma over-screening and plasma fluxes
* 3. Helical dust structures
* 4. Replication of helical dust structures
* Acknowledgment
* Appendix
o A.1. Methods used for description of plasma crystal
o A.2. Numerical simulation methods
* References

1. Introduction

A universal definition of life [1] relates it to autonomy and open-
ended evolution [2], i.e. to autonomous systems with open-ended
evolution/self-organization capacities. Thus a number of features
follow: some energy transduction apparatus (to ensure energy current/
flow); a permeable active boundary (membrane); two types of
functionally interdependent macromolecular components (catalysts and
records)–in order to articulate a genotype-phenotype’ decoupling
allowing for an open-ended increase in the complexity of the
individual agents (individual and collective’ evolution) [3]. The
energy transduction system is necessary to feed’ the structure; the
boundary as well as a property called autopoiesis’ (which is a
fundamental complementarity between the structure and function [4, 5])
are necessary to sustain organized states of dissipative structures
stable for a long period of time. To maintain a living organic state,
it is also necessary to process nutrients into the required
biochemical tools and structures through metabolism which in
mathematical terms can be seen as a mapping f that transforms one
metabolic configuration into another (and is invertible) f(f) = f;
i.e. it is a function that acts on an instance of itself to produce
another instance of itself [6, 7]. Finally, memory and reproduction of
organic life are based on the properties of DNA which are negatively
charged macromolecules exhibiting an important property of replication
[8].

Self-organization of any structure needs energy sources and sinks in
order to decrease the entropy locally. Dissipation usually serves as a
sink, while external sources (such as radiation of the Sun for organic
life) provide the energy input. Furthermore, memory and reproduction
are necessary for a self-organizing dissipative structure to form a
living material’. The well known problem in explaining the origin of
life is that the complexity of living creatures is so high that the
time necessary to form the simplest organic living structure is too
large compared to the age of the Earth. Similarly, the age of the
Universe is also not sufficient for organic life to be created in a
distant environment (similar to that on the Earth) and then
transferred to the Earth.

Can faster evolution rates be achieved for non-organic structures, in
particular, in space consisting mostly of plasmas and dust grains,
i.e. of natural components spread almost everywhere in the Universe?
If yes, then the question to address is: are the above necessary
requirements of self-organization into a kind of a living creature’
present in plasmas containing macro-particles such as dust grains?
Here, we discuss new aspects of the physics of dust self-organization
that can proceed very fast and present an explanation of the grain
condensation into highly organized structures first observed as plasma
crystals in [9, 10]. We stress that, previously, important features of
these structures were not clearly related to their peculiar physics
such as plasma fluxes on to grain surfaces, sharp structural
boundaries, and bifurcations in particle arrangements that can serve
as memory marks and help reproduction. The plasma fluxes strongly
influence interactions of dust particles, sustain the boundaries, and
realize the energy transduction. We discuss experiments which indicate
the natural existence of the memory marks in helical dust structures,
similar to DNA, and natural mechanisms of the helical dust structure
reproduction.

2. Plasma over-screening and plasma fluxes

An important feature of inorganic structures is the presence of
memory marks’ existing as rigid marks’ in common crystal systems. In
contrast, observations of crystals formed by dust in a plasma (plasma
crystals) [9, 10] demonstrate no rigid marks because of unusual
properties of plasma crystals such as large coupling constant, low
temperature of phase transition, and large separation of grains. These
puzzling properties can be resolved by employing the over-screening of
grain fields, the effect that was clearly realized only recently. The
over-screening appears in the presence of plasma fluxes on to the
grain surfaces [11]-[13]. As a result, an attraction well appears as
indicated schematically in figure 1. This potential well is usually
shallow and located at a distance much larger than the Debye screening
length λD (an example shown in figure 1 uses parameters typical for
plasma crystal experiments [9, 10]). A shallow potential well explains
the large coupling constant as well as the low temperature of phase
transitions. By extracting the pure Coulomb potential of interaction
and introducing the screening factor ψ, the grain interaction
potential is V = Zd2e2ψ/r (Zd is the grain charge in units of electron
charge -e). Due to over-screening, the value of ψ changes its sign at
large distances as indicated in figure 1. At the potential well
minimum, the screening factor ψmin is negative. The value |ψmin|
determines the temperature of the associated phase transition Td and
also characterizes the distance rd = rd(|ψmin|) of the well minimum
(in the simplest case, r_{\rm d}\approx 1/\sqrt{\vert\psi_{\rm min}
\vert} ). If condensation of grains (or grain pairing) occurs, the
grains will be localized at the minimum of the attraction well, rd.
The corresponding criterion can be expressed through the coupling
constant Γ (which is the ratio of the potential energy of the grain
interaction to their kinetic energy) as Γ > Γcr≡Zd2e2/rdTd = 1/|ψmin|.
Thus, |ψmin| determines values of the inter-grain distance, the
temperature of transition, and the coupling constant. For a shallow
attractive well, |ψmin| ll 1 and Γ gg 1. This qualitatively explains
thelarge value of Γ observed in experiments. The model predicts Γcr to
be of the order of the difference between the maximum grain
interaction and the temperature of transition (about 3-4 orders of
magnitude). As a result, the concept of plasma over-screening agrees
well [12, 13] with major experimental observations [9, 10]. It also
applies for description of dust helical structures and leads to the
possibility of unusual memory marks’ impossible in common crystals.

Figure 1

Figure 1. Sketch of the screening factor ψ of the grain interaction
potential. The grain interaction energy V can be described in units of
pure (not screened) Coulomb interactions of grains V = ψ(Zd2e2/r) as a
function of the distance between the grains in units of the linear
Debye screening length. The distance rd displays the position of the
minimum of the attraction well and has a typical experimental value of
200 μm [9, 10]. This corresponds to the inter-grain distances observed
during the phase transition to the plasma crystal state. The value of |
ψmin| varies between 10-2 and 10-4 for different models and different
experiments. This value is in accordance with the ratio of the
interaction at the minimum of the potential well and the maximum
interaction energy corresponding to ψ = 1, respectively. The value of
coupling constant Γ = 1/|ψmin| ranges from 102 up to 104 in accordance
with observations.

We have performed molecular dynamics simulations to demonstrate that a
random distribution of grains, interacting via the potential shown in
figure 1 with a shallow attractive well |ψmin|approx10-3 and
experiencing background friction and stochastic kicks, forms spherical
grain crystals. In figure 2, we show results of these simulations.
Application of this model is of double importance. Firstly, we resolve
the problems of laboratory observations, and secondly, we predict the
possible existence of large plasma poly-crystals in space–a new state
of matter which is unexplored so far. Here, an important point for
space applications is that the attraction potential well is shallow
and therefore even weak dissipation can cause the grain capture in the
well.

Figure 2

Figure 2. Molecular dynamics simulations of dusty cloud evolution. The
figure shows snapshots of the velocity field and grain positions: (a)
corresponds to the initial state (t = 0) of the cloud, (b) t = 0.3 s
and (c) t = 3 s, respectively. The velocity magnitude is color-coded.
It rises from blue to red by a factor of five. Initially, 103μ m-size
(see figure 1) and the pair interactions between grains are described
by the potential shown in figure 1. Grain motions are damped by
friction (to model viscosity of plasma neutral component) and
stochastically accelerated by Langevin force (to model plasma
fluctuations). The simulations reveal formation of a stable self-
confined spherical structure in time. Local order analysis shows that
some grains (about a few percents of their total number) have hcp
lattice type, while the majority of grains are in a liquid state.

Physically, the attraction appears due to the electrostatic self-
energy of grains, supported by plasma fluxes continuously absorbed by
the grains. The fluxes are necessary to sustain the grain charges and
appear almost immediately as soon as a particle is embedded in the
plasma. The self-energy of grains is much larger than their kinetic
and potential energies so that its (even small) changes can strongly
influence grain interactions. It was first shown in [11] that for a
fixed source of plasma fluxes, the electrostatic energy of two grains
decreases when they approach each other. As the self-energy is
supported by continuous plasma fluxes, work has to be done to maintain
them and this can almost compensate the associated changes of self-
energy. Nevertheless, a full compensation does not occur if the
distance between the grains is large. At present it is understood [12,
13] that this phenomenon is a general feature of grain interactions in
a plasma. The fluxes on grains depend on the electrostatic
polarization charges of the grains and the polarization charges depend
on the fluxes and create an accumulation of excess plasma charges
between the grains. These plasma charges exhibit the sign opposite to
that of likely charged interacting grains and therefore cause the
attraction. The appearance of grain attraction is a general phenomenon
which converts the grain containing matter into a new unusual state.

Effects of plasma fluxes lead to gravitation-like instabilities with
an effective gravitational constant GeffapproxZd2e2|ψminmd2. For a
dust size aapprox3 μm, a mass density of the dust material of 2g cm-2,
Zdapprox103 and |ψmin|approx10-4, the effective gravitational constant
Geff is approximately 6×104 cgs which is 1012 times larger than the
usual gravitational constant G = 6.7×10-8 cqs. The effective Jeans
length of this instability has the size of order rd. The effective
gravity affects only dust grains and therefore plasmas can be
influenced by this attraction only through their interactions with the
grains. The new effective instability of a dusty plasma leads to
structurization of dust clouds similar to the effects caused by the
usual gravitational instability.

Dust structures self-organized in the plasma environment have sharp
boundaries such that they are isolated from each other by regions
without grains (dust voids). This effect, observed in the laboratory
as well as in micro-gravity experiments onboard the ISS [14], is well
explained theoretically [15, 16]. The structures and crystals should
self-generate additional confining forces due to the plasma fluxes
directed into the structures, i.e. these structures serve as sinks of
plasmas and the ram pressure of the plasma fluxes acts on the
structures to make them self-organized, self-confined and dissipative.
This self-contraction should be added to the the grain pairing; their
joint effect leads to formation of dust helical structures.

3. Helical dust structures

Helical dust structures (an example is given in figure 3(a)), can be
considered as equally separated flat structures with constant rotation
angle between the planes (figure 3(b)). Their properties are of
special interest for the problems discussed here. Figure 3(a)
illustrates double helical dust structures similar to DNA. Molecular
dynamics simulations of interacting grains with an additional gas
friction show that any cylindrically symmetric grain distribution
converts in time into a stable self-confined helical structure [17].
These specific stable dust structures form due to the grain pairing
attraction as well as due to the external plasma flux created by the
whole structures (and the anticipated ram pressure). In experiments in
gas discharges with a longitudinal external electric field forming
striations [18, 19], modulated cylindrical grain crystals were
observed. As predicted by numerical simulations [17], these
cylindrical crystals convert into helical structures with fewer grains
per unit length. According to numerical experiments, highly symmetric
spherical dust structures can be formed only when the spherical
symmetry is externally supported (e.g. when all initial conditions are
spherically symmetric). In the other cases, even a small asymmetry
leads to formation of cylindrically symmetric and/or helical
structures. In nature, some asymmetry always exists and therefore
formation of helical structures is quite probable. First observations
of dust self-confined moving helical structures were done in dc
cryogenic gas discharges [20]. The particle traces, moving in a self-
organized way, are shown in figure 4. Similar ion helical structures
were also observed in laser cooling traps [21].

Figure 3

Figure 3. (a) and (b) Sketch of helical double winding grain
structures similar to DNA. (c) Bifurcations in (phi,D/Δ)–plane of
structures confined by external potential Kr2/2; phi is the rotational
angle in each plane of the helical structure; D is the diameter of the
helical structure and Δ is the spatial separation of the planes of the
helical structure; the line K = 0 corresponds to self-organized stable
structures without external confinement K = 0 but with the presence of
dust attraction [17].

Figure 4

Figure 4. (a) Traces of helical structures on the walls of the chamber
observed in dc cryogenic plasmas at Ti = 2.7 K. The traces of conical
helical structure are shown black on the green background of discharge
at several distances from the top of it; x = 0 mm–the head’ of the
structure, x = 3 mm–the middle of the structure and 5 mm–the end of
the structure. The whole structure looks like a worm’, hollow inside
(having a dust void inside) and moving on cylindrical surfaces around
the axis of discharge. (b) Sketch of the central part of the helical
structure of the worm’ deduced from the traces left of the structure
on the wall of the discharge chamber, the grains are located at the
surfaces of a few cylinders inside each other [20].

Important features of dust helical structures observed in simulations
[17] and indicated by analytical investigation of stability of helical
structures and mode oscillations is the existence of numerous
bifurcations in the dependence of the helical winding angle upon the
diameter of the structure. An example of this helical structure
behavior is demonstrated schematically in figure 3(c). Bifurcations in
helical structures appear naturally and correspond to the critical
conditions when any slight change in the helical structure diameter D
results in a sudden change of the helical winding. We note that
various helical structures with different bifurcations can be obtained
in experiments using current cylindrical discharge plasma crystals by
continuously decreasing the number of grains injected into the system.
Numerical investigations show a universal character of these
bifurcations. The helical structures have the unique property of
bifurcations which can serve as memory marks. With increasing of
diameter of the structure suddenly the rotational angle of the
structure is changed. This is illustrated by figure 3(c) which shows
that an increase of diameter of the structure at certain radius there
appears possibility of presence of two equilibrium vales of the
rotational angle (the upper thick dashed line and the lower solid
line) instead of one possible equilibrium value for the rotational
angle before bifurcation (the upper thick line). After the bifurcation
the solid thick dashed line represents an unstable branch and the
solid lower line represents a stable branch. Thus the rotational angle
at some critical radius is changing abruptly.

These bifurcations can serve as possible memory marks for the
structures. The helical crystals can then store this information.

4. Replication of helical dust structures

Dust convection and dust vortex formation outside the structure is
another natural phenomenon observed in laboratory experiments and in
experiments onboard the ISS [14]-[16]. The physics of dust vortex
formation is related to the grain charge inhomogeneity and its
dependence on surrounding plasma parameters. The gradients of grain
charges are supported self-consistently by the structure, and they are
the reason for the non-potential character of the electrostatic force –
eZdE acting on the grains and causing the vortex formation. Dust
convection was observed in experiments on cylindrical dust crystals
formed in modulated gas discharges [18] (figure 5(a)) and was obtained
in numerical modeling [19] (figure 5(b)). It is important that the
helical crystals modulated in their radius are always surrounded by
self-created dust convection cells. The helical dust structures, after
they are formed, resemble features similar to those of DNA. In
particular, they can transfer information from one helical structure
to another via the dust convective cells surrounding any bifurcation
of the helical structure. A rough sketch of a possible model of the
helical grain structure reproduction is shown in figure 5(c).

Figure 5

Figure 5. (a) The observed grain convection surrounding the
cylindrical grain crystal. Different colors correspond to different
grain velocities [18], The velocities vary from about 0.4 cm s-1
(blue) up to 1.5 cm s-1 (red). (b) The dust convection obtained in
numerical simulations [19]. (c) Sketch of the model for helical
structure duplication (reproduction). See details in the text.

Let us discuss some details about possible sequences of events during
the reproduction. The abrupt change of the rotational angle will
create an inhomogeneity in random halo dust grains surrounding the
helical structure with grain charge gradient not collinear to the
electric field and will create a force forming pair of toroidal
vortices around the structure. For a negatively charged structure the
upper toroidal vortex has a clockwise rotation while the lower has an
anti-clockwise rotation. If another (second) helical structure has no
bifurcation and moves close to that with bifurcation the vortices
start to be created in this structure. Finally these vortices create
the bifurcation in the second structure and transfer the information
from the first structure to the other one.

The evolution of dust structures in the presence of plasma fluxes is
related to the characteristic frequency of dust motions. In first
instance, this can be estimated by the dust plasma frequency
ωpd~(Zd2e2/mdrd3)1/2, where md is the mass of a dust particle. We note
that characteristics of the potential well (located at rd) and
therefore the physics of plasma fluxes enter this expression via rd
and Zd. This consideration destroys one of the current myths in
astrophysics, namely, that the grain interaction is vanishing for
distances larger than the linear Debye screening radius. This is
obvious since inside the dust Jeans length (where the interactions are
still effective) many grains are present for most dust clouds in
space. For most situations, the plasma dust frequency of a few (or
even a fraction of) Hz leads to times extremely short compared to
typical astrophysical times. If grain structures exist in space, they
have collective modes of oscillations which in principle can be
detected as modulations of the infrared emission of different cosmic
sources. The effective Jeans size of dust clumping is in the range
that can be detected by the Spitzer telescope in observation of (the
closest to the Earth) formations of dust clouds around stars and star
outbursts preceding the formation of new planetary systems. The
program to measure low frequency regular modulations from dust clouds
with the effective structure sizes caused by the dust attraction
instability can be included in, e.g. the Spitzer telescope project.

Our analysis shows that if helical dust structures are formed in
space, they can have bifurcations as memory marks and duplicate each
other, and they would reveal a faster evolution rate by competing for
food’ (surrounding plasma fluxes). These structures can have all
necessary features to form inorganic life’. This should be taken into
account for formulation of a new SETI-like program based not only on
astrophysical observations but also on planned new laboratory
experiments, including those on the ISS. In the case of the success of
such a program one should be faced with the possibility of resolving
the low rate of evolution of organic life by investigating the
possibility that the inorganic life `invents’ the organic life.

Acknowledgment

This work was partially supported by the Australian Research Council.

Appendix

A.1. Methods used for description of plasma crystal

Special methods have been developed to treat the plasma over-screening
for present experiments with large grain charges which cause the
screening to be nonlinear at short distances between the grains [9,
10]. The full nonlinear treatment of the screening polarization
charges and plasma fluxes is rather complicated [12]. The progress was
achieved on the basis of physical arguments showing that close to the
grains the influence of fluxes on polarization is small. Neglecting
the effect of fluxes the nonlinear screening was solved in [13] by
using the approach of [22]. Far from the grain the coupling of fluxes
and polarization charges became important but the polarization charge
became small and one can use the linear approach to find the coupling.
The matching method at the distances where the nonlinearity starts to
be weak have been applied successfully [13] to describe the nonlinear
over-screening.

A.2. Numerical simulation methods

The cooperative behavior of charged grains embedded in a plasma is due
to electrostatic coupling between the charged particles, which are
believed to interact via a potential which has both a repulsive and an
attractive short-range component. 3D molecular dynamics simulations
including electrostatic collisions between grains, neutral drag and
stochastic Langevin force were performed to simulate the evolution of
a dusty cloud. Free boundary conditions were used. To analyze the
local order of grains, we used the bond order parameter method [23].

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