BINARY PLANET X BIOLF

In comparing Earth to other planets of similar size and circumstance when asking why Earth has life (or is alive) and the others appear not to, it makes sense to ask what is different about the Earth. The most notable difference that is strangely rarely mentioned is the Moon. Our moon is roughly 25% the size of Earth (it is only 1/8th the mass, but ~25% by volume), making it the largest satellite relative to the size of its parent planet we know around a planet of sufficient size to possible contain life (Pluto's moon, Charon, is of similar relative size, but Pluto is far too small to retain an atmosphere). In fact, our moon is so large relative to the Earth that, technically, the Earth and Moon should be considered a double planet. The size of our planetary sibling has a major impact on the Earth, on our tides, the action of plate tectonics, the behavior of life, and probably other things I am overlooking. But the active impact of the Moon may not even be its biggest impact where life is concerned. The manner of its birth may be the real differentiator.

The leading theory is that the Earth collided with a Mars-size planet early in its existence; the Moon being the progeny of that union. In addition to Earth having an unusually large satellite, another consequence of that collision that may have had a critical impact on the viability of life on Earth is that Earth probably has a disproportionately large, and perhaps more molten iron / nickel core, and thereby also a hotter mantle. This seems likely because the Moon is much smaller than Mars and available data suggests its core is less than 3% of its mass, even though it's likely the original body with which the Earth collided would probably have had a relatively larger iron core. It makes sense that the "missing" core material was added to the core of the Earth, giving it an unusually large core for its size. This would explain where the rest of the original Mars size body went. It might also have resulted in Earth enjoying a higher level of plate tectonics compared to its similar size neighbors, thus making it more conducive to sustaining life as the author suggests.

Could it be that such planetary twins are necessary to bring a planet to life? Perhaps, rather than searching for Earth-like planets, we should be searching for similar planetary twins?

- The other comment/question is that, if life is something that happens to a planet, not just on it--meaning a planet is either alive or not--what is the relationship between intelligent life and a planet? Does the Gaia concept suggest that a planet can be, not just alive, but also, at some point, sentient?