Osservatorio Astronomico di Palermo Giuseppe S. Vaiana

EXPERIMENTAL ASTROBIOLOGY

The study of the origin, evolution and distribution of life in the universe is the groundwork of Astrobiology/Astrochemistry. This is a multidisciplinary science in which astrophysics, physics, chemistry, biology and geology work in synergy to answer the following questions: How did life originate on Earth and how did it evolve? Is there life in space and how can we find evidence of it? There is increasing consensus among the scientific community on the hypothesis that we cannot understand the origin and evolution of life unless our scenario goes far beyond the restrictive limits of our own planet. This new perspective has its foundations on the ever-increasing amount of discoveries of organic molecules in interstellar clouds, and amino acids and other biologically relevant material - i. e. molecules that are commonly found in proteins - in meteorites.

Observations and theoretical models suggest that planetary systems like ours came from dense inter- stellar clouds made of gases and dust particles which, because of gravity, collapsed to form a central star, the planets and a large amount of minor celestial objects such as small grains, meteorites and comets, relicts of the primordial nebula. In the newly formed planetary system, planets undergo heavily bombarded by such relicts receiving an enormous amount of organics.

For instance, over the first 320 million years of its life, more than a thousand times the actual biomass settled on Earth. Hundreds of organics molecules have been so far detected in space and some of them very important for life including amino acids found in meteorites, and some of them are of biological relevance, i.e commonly found in proteins.

From this hypothesis other questions arise: what kind of processes has led to the formation, in space, of complex molecules such as amino acids? And how could they survive the ionizing solar radiation? Solar radiation, if on one hand can cause damage to prebiotic material, on the other is crucial in supplying the energy required for the synthesis of prebiotic molecules in interplanetary space. Although several models have been recently proposed to explain amino acid formation in space, we still do not know what role exogenous prebiotic molecules play in the origin-of-life process.

Moreover, amino acids, and more in general organic material, are easily photo-degradable and with lack any suitable protective mechanism, it is unlikely that they could have survived in harsh interplanetary space and on Earth primordial environment.

So, although the hypothesis that basic life molecules are exogenous is well observed and experimented, it is far from representing a co-coherent and complete theory for the origin of life.

The OAPa LIFE (Light Irradiation Facility for Exochemistry) laboratory.

In 2006 a laboratory for astrobiology/astrochemistry was set up, in order to study the role of X and UV radiations coming from young Sun-like stars, in the synthesis of organic molecules, particularly amino acids, in space.

The interplanetary space conditions are simulated by means of a ultra high vacuum chamber (10^-11 mbar), provided with a pumping system, a cryostat through which temperatures of 10 K (about -263 C) can be reached, X and UV radiations sources simulating emissions from the young sun, and several measuring instruments. Although the laboratory is still under development a series of experiments have been performed so far. Studies of the effects of soft X-ray radiation on DNA molecules (Ciaravella et al 2004) and amino acids (Ciaravella et al 2010) have shown the competing processes, e.g. destruction versus formation of new structures (dual role of radiation). In particular, DNA molecules from Bacillus Subtilis were irradiated in water solution at room temperature, simulating terrestrial environment, with and without presence of clays in the solutions.

The results have pointed out the important role of clay, a key component in the formation of complex molecular structure, in protecting the molecules from the radiation damage. In the amino acids experiment along with the destruction of the tryptophan molecules large molecular structures, such as tryptophan dipeptide and tripeptide have been observed. Studies of soft X-ray irradiation of interstellar ice analogues have shown that X-rays are more efficient than typical used, HI Ly (121.6 nm), ultraviolet radiation in producing new complex species (Ciaravella et al 2010, Ciaravella et al. 2011).

Relevant references

1) Ciaravella A., Scappini F., Franchi M., Cecchi-Pestellini C., Barbera M.Candia R., Gallori E., Micela G., Role of Clay on Adsorbed DNA against X-ray Radiation, 2004, International Journal of Astrobiology, Vol.3 (1), 31.

2) Ciaravella A., Muñoz Caro, G., Jimenez Escobar, A., Cecchi Pestellini, C., Giarrusso, S., Barbera, M., Collura, A. Soft X$-$ray Irradiation of a Methanol Ice: Implication for H2CO Formation in Interstellar Regions, 2010, ApJL, 722, 45

3) Ciaravella A., Bongiorno, D., Cecchi-Pestellini, C., Testa, M.L.,Indelicato, S., Barbera, M., Collura, A., La Barbera, A., Mingoia, F.,The Young Hard Active Sun: Soft X-ray Irradiation of Tryptophan in Water Solutions, 2011, Int. J. of Astrobiology, 10(1), 67

4) Ciaravella A., Jimenez Escobar, A., Muñoz Caro, G., Cecchi Pestellini, C., Candia, R., Giarrusso, S., Barbera, M., and, Collura, A. Soft X-ray Irradiation of Pure Carbon Monoxide Interstellar Ice Analogues, 2011, ApJL, in press