Search for chiral molecules and optical activity in extraterrestrial systems. Example of Titan.

One of the main characteristics of terrestrial life is the role of optically active organic substances. Thus a search for chiral compounds and optical activity on an extraterrestrial body may give an indication of the presence of life, either fossilized or still in existence. If only abiotic conditions are prevailing the same search may still provide interesting information on the possible origins of homochiral families of biomolecules on Earth (e.g. the amino acids). In this respect, Saturn's satellite Titan is exemplary. A list of some of the most simple chiral derivatives devoid of oxygen atoms possibly present on Titan is presented. The interest of an investigation of optical activity is discussed taking into account some significant parameters. This raises numerous difficult technical problems which once solved may be helpful for further exploration of other planets.