Circularly polarised radiation in early proto-planetary systems

The discovery of strong 17 per cent circular polarisation in the IR in the Orion OMC-1 star forming region (Bailey et al. 1998, Science 281, 579) has provided a new impetus to the view that the homochirality of natural amino-acids seen in biological systems on Earth may have been triggered by asymmetric photolysis of biogenic amino acids in space through the action of circularly polarised radiation. The circular polarisation seen in OMC-1 has been attributed to scattering of linearly polarised light by dust grains that have been aligned by magnetic fields in the molecular cloud complex. There is no direct evidence that the high levels of CP observed in the IR will extend to the UV spectral region which is known to carry circular dichroism bands that may be responsible for the asymmetric photolysis, but this is expected to be the case.

The scattering geometry required to make the proposed mechanism work is very special. The proto-planetary system will need to be shielded from the direct glare of the source of the unpolarised primary radiation that is being scattered by the dust cloud assumed to be an early type star. Given the clumpyness of the dusty environment of Orion, this is not implausible. However, the process needs to be modelled to estimate the fraction of proto-planetary systems that may be subjected to such a process. The student will be expected to review this field, and to use an existing code on dust extinction to construct such a model. The project will be supervised in collaboration with Dr Jeremy Bailey of the Anglo-Australian Observatory in Sydney.