Evolution of primordial planets in relation to the cosmological origin of life

摘要

We explore the conditions prevailing in primordial planets in the framework of the HGD cosmologies as discussed by Gibson and Schild. The initial stages of condensation of planet-mass gas clouds is set at 300,000 yr (0.3My) following the onset of plasma instabilities when ambient temperatures were >1000K. Eventual collapse of the cloud into a solid structure, dominated by water-ice and organics takes place against the background of an expanding universe with declining ambient temperatures. Isothermal free fall collapse occurs initially via quasi equilibrium polytropes until opacity sets in due to molecule and dust formation. The contracting cooling cloud is a venue for molecule formation and the sequential condensation of solid particles, starting from mineral grains at high temperatures to ice particles at lower temperatures, Water-ice becomes thermodynamically stable between 7 and 15 My after the initial onset of collapse, and contraction to form a solid icy core begins shortly thereafter. The icy planet core, which includes a fraction of radioactive nuclides, 26A1 and 60Fe, melts through interior heating. We show, using heat conduction calculations, that the interior domains remain liquid for tens of My for 300km and 1000km objects, but not for 30 or 50km objects. Initially planets are separated by relatively short distances, measured in tens to hundreds of AU, because of the high density of the early universe. Thus exchanges of materials, organic molecules and evolving templates could readily occur providing optimal conditions for an initial origin of life. The condensation of solid molecular hydrogen as an extended outer crust takes place much later in the collapse history of the protoplanet. When the object has shrunk to several times the radius of Jupiter, the hydrogen partial pressure exceeds the saturation vapour pressure of solid hydrogen at the ambient temperature and condensation occurs.