Hi All

The Sun is depleted in O-16 with respect to the planets, thanks to Apollo moon samples just recently analysed.

Odd Sun

If the Sun and the planets are cut from the same cloth this is very odd.

But what if they're not? Michael Woolfson's Capture Theory suggestions the planets formed from a tidally distorted proto-star, some 1000 AU across - that encountered the Sun. As it was distorted it formed a long filament that collapsed via Jeans collapse into several planets that were then captured by the Sun on highly elliptical trajectories. The major planets underwent collapse before their first perihelion, thus surviving as bound masses, but tidally bulged enough to in turn fling off mass to form their moons.

This occurred in the birth nebula of both stars during the nebula's high density embedded stage (some nebulae have stellar densities of 100,000 stars per cubic parsec) so the number of tidal events was quite high - up to 20% of stars. But there was probably quite distinct chemistry across the nebula, so quite pronounced differences in isotopic abundances are feasible.

Adam

PS In this scenario Earth and Venus are the remnant cores of two smallish gas giants that collided during a period of rapid precession as their orbits were circularised by drag in the Sun's dust-disk. This collision was hot enough to create all sorts of odd isotopes that are scattered through out the solar system too.