CapitalistImperialistPig

The equations of motion that govern the Solar System are chaotic . So a kind of important question is that of whether planetary orbits are stable. The best available answer seems to be maybe. When simulations are run for a few billion years, some funky stuff sometimes - but only rarely - happens. Sometimes Mercury collides with Venus. Sometimes with the Sun - or, more usually, neither. Sometimes Mars gets ejected from the Solar System. Gravitational micro-lensing observations seem to show that there are a certain number of orphan planets out there, planets that apparently formed in stellar systems but subsequently hit the road after getting ejected from their birth systems. There are even hints that such an event might have occurred early in the history of our Solar System. One puzzling event of early solar system history is the so-called Late Heavy Bombardment. One theory sanctioned by dynamic simulation is that this asteroid bombardment, some 300-500 million years after...

The metallicity of a star, we might recall, measures how much of its material consists of elements heavier than hydrogen and helium, that is, those elements that were manufactured in earlier generations of stars that subsequently spewed their contents across the cosmos. Our Sun, for example, has about 1 iron atom for every 20,000 hydrogen atoms. Metallicities of other stars are measured on a logarithmic scale on which the Sun is defined to have metallicity zero. Thus, a star with metallicity -4 has an iron fraction only 1/10000 that of the Sun (1 iron atom for every 200 million hydrogen atoms). The most metal poor stars of all seem to have metallicities of about -4.5, while the most metal rich are near 1, with ten times more iron than the Sun. Since the very first generation of stars had no metals at all, these would have been off the scale in the negative direction, but none of these so-called Population III stars seem to have survived to the present. The kinds of planets a st...