Earth, every moon and every asteroid together barely register on the Solar System's scales
Put the whole Solar System on a balance and the Sun alone accounts for 99.86 percent. Of the scraps left over, the four giant planets take 99 percent. Everything else, including Earth, Mars, Venus, Mercury, all the moons, dwarf planets, asteroids and comets, adds up to under 0.002 percent of the total.
The lopsidedness goes back to formation, at least 4.568 billion years ago, when part of a vast hydrogen-rich cloud collapsed. Spinning faster as it shrank, it flattened into a disc about 200 times the Earth-Sun distance across, with a hot protostar at the centre. Close in, the heat drove off carbon-bearing compounds for the first million years, beyond a boundary nicknamed the soot line, and only metals and rock could stay solid. Those materials were a small share of the raw stock, so the inner planets stayed small.
Farther out, past the frost line between Mars and Jupiter, ices could freeze. They were far more plentiful, letting young planets grow big enough to grab thick envelopes of hydrogen and helium. Hundreds of protoplanets may have formed, but most merged, broke apart or were flung away. Leftover debris gathered in the asteroid belt, the Kuiper belt and the distant Oort cloud, the reservoir of long-period comets that may stretch beyond 2,000 times the Earth-Sun distance.
Some moons rival planets. Ganymede and Titan are larger than Mercury, though less massive, and seven moons, our own among them, outweigh every dwarf planet. The Sun's wind blows until it meets interstellar gas around 70 to 90 times Earth's distance, while its gravity holds sway far beyond, out to nearly three light-years.
The arrangement will not last forever. When the Sun runs out of core hydrogen in about 5 billion years it will swell to roughly 260 times its present width as a red giant, likely vaporising Mercury and Venus and leaving Earth uninhabitable. Eventually it will shed its outer layers and shrink to an Earth-sized white dwarf holding about half its original mass.
Source: Solar System
