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Planet Formation

Newly born stars that will evolve to become similar to the Sun grow by accretion from the discs surrounding them. In turn, the stars emit radiation that ionises and heats parts of the discs and material falling onto them. The achievement of an understanding of how planets form in many such discs will require insight into a wide range of physical and chemical processes and how they govern the large-scale dynamics.

Water Snowline
An artist's impression of the water snowline around the young star V883 Orionis.
Credit: A.Angelich (NRAO/AUI/NSF)

At Leeds we are interested in the origins of planetary systems. The rate at which new exoplanets are detected has increased continuously. The growing database on the architectures of planetary systems presents an exciting challenge to researchers investigating how planets emerge from discs of gas, dust, and ices. The dust and ices become major constituents of terrestrial planets like the Earth, but dusty, icy particles also carry much of the electric charge and current controlling the roles that magnetic fields and turbulence play in disc evolution and planet formation. The chemistry occurring on the dusty icy particles can create complex organic molecules, including prebiotic molecules such as amino acids. Some of these large molecules return to the gas phase and are targets of observations conducted by Leeds staff.

In particular, Leeds researchers have competed successfully against scientists in the top universities and research institutions throughout the world to win substantial observing time on the world's largest ground-based observatory, ALMA, to study protoplanetary discs. This billion-pound facility, designed to detect 0.32 to 3.6 mm radiation and consisting of 66 receivers, including 50 dishes that can be separated by up to 16 km and that are 12 metres in diameter, allows unprecedented high resolution enabling us to probe the dust and gas within a disc at the scales on which planets form.

These studies on proto-planetary discs are soon to be complimented by theoretical work looking at how magneto-rotational instabilities (MRI) generate turbulence in the disk. This will combine dust physics, such as grain collisions and grain growth, with MRI turbulence simulations to create models that can be compared with observational results.

Gravitational Instabilities
Assessing the implications of gravitational instabilities on the chemical evolution of a young, self-gravitating protoplanetary disc. Log gas-phase column densities of species at the end of the simulation. Gas-phase fractional abundances are significantly affected by chemical reactions.
Figure from: Evans, M. G. et al. 2015, MNRAS, 453, 1147.