Possible cometary organic compounds as sources of planetary biospheres

Abstract

Various organic compounds including complex organic compounds have been detected in comets. Cometary organics are supposed to be formed in interstellar dust (ISD) environments. We examined possible formation of bioorganic compounds in ISDs through simulation experiments, and compared with that in primitive Earth atmosphere. It was shown that a wide variety of amino acids were formed in simulated ISD environments in the form of precursors. Pyrimidine bases (uracil, cytosine and thymine) were also formed from the possible interstellar media. These results suggest that comets can bring no less types of bioorganics to planets than those formed in primitive Earth atmosphere. Not only Earth, but also other planetary bodies like Mars and Europa received cometary organics during the late heavy bombardment era. They can be included in possible habitable areas whatever primitive planetary atmosphere they had.

Glycine oligomerization up to triglycine by shock experiments simulating comet impacts

“…This fact is also suggested by laboratory experiments carried out on simulations of interstellar ice analogs, which resulted in the production of various amino acids; accordingly, their relationships to cometary amino acids were proposed (e.g., McPherson et al, 1987;Bernstein et al, 2002;Muñoz Caro et al, 2002;Kobayashi et al, 2004;Holton et al, 2005). The detection of glycine in cometary grains confirmed the existence of an amino acid in comets (Elsila et al, 2009).…”

Organic matter in space: from star dust to the Solar System

“…Proton irradiation of carbon monoxide, nitrogen and water under simulated interstellar conditions has been shown to be able to yield uracil, one of the four RNA bases (the others being cytosine, adenine, and guanine). Thymine, the base that substitutes for uracil in DNA, has been reported to be present under proton irradiation of a mixture of methane, carbon monoxide, and ammonia (Kobayashi et al 1995(Kobayashi et al , 2004.…”

Experimental verification of photostability for free- and bound-amino acids exposed to γ-rays and UV irradiation

“…Dose rate, which was measured with a Fricke dosimeter (Ikeda and Suzuki, 1998). Then, the mixtures were subjected to UV photon (wavelength, over 160 nm) under a 150 W deuterium lamp (L1835; Hamamatsu Photonics) equipped with a UV irradiation window and a synthesized quartz window at a dose rate of 2.05 J/h for 24 hours (Takano et al, 2002(Takano et al, , 2003Kobayashi et al, 2004). Since irradiation window was attached with quartz window, above 160 nm wavelength was obtained.…”

“…Kasamatsu et al (1997) showed that amino acid precursors (molecules which are hydrolyzed to amino acids) could be formed by irradiating an icy mixture of carbon monoxide, ammonia and water with high energy protons. The energy yields (G-value rate, the number of formed molecule/100 eV of glycine) with γ -rays and UV irradiation were found to be independent of the starting material phase (Takano et al, 2002;Kobayashi et al, 2004).…”