| MadSci Network: Astronomy |
Hi Sybil,
Thank you for your question. Let's first start with your comment that gold is created by exploding stars[1]. This is true. Our solar system consists of the remnants of an earlier supernova, and material that has been there since the Big Bang. It is not unlikely that the shock of the supernova triggered the formation of the Sun. Now, it is not unreasonable to assume that the distribution of mass in the cloud was initially fairly uniform. This means that all the heavier elements, which means heavier than hydrogen and helium, could have been distributed fairly evenly in the cloud.
At this point, the shock of the supernova, or another cause, would cause the cloud to condense. The condensed bits of matter would have a stronger gravity, and attract more matter, creating lumps that would eventually form the planets. The big lump in the center would become the Sun. At this point, the composition of the planets might still be quite even.
When the Sun started forming, it started to produce heat. This heat increased the temperature of the inner planets, "boiling off" much of the volatile gases, such as hydrogen and helium. Even though there is quite some hydrogen left on Earth, it is only a tiny fraction of what must have been there initially, as the overwhelming majority (about 75%) of the matter in the Universe is hydrogen, and the Earth is mostly iron, oxygen and silicon[2]. As a result, the outer planets (Jupiter, Saturn, Uranus and Neptune) are a lot bigger, but also have a lot less heavier elements, relatively speaking, including gold.
This leaves the terrestrial planets Mercury, Venus, Earth and Mars. These planets do not have the same composition. One hypothesis is that the planets may have had a similar composition, but some of them had their (lighter) outer layers stripped off by an impact. This Giant Impact Hypothesis is used to explain why the Moon is relatively a lot less rich in heavier metals, such as iron. This also means that the amount of gold on the Moon is likely to be less than the amount of gold on Earth, both relatively and absolutely.
Your question becomes even more difficult to answer when we consider that planets have an internal structure. Typically, the heavier elements, such as iron, are in the core, while the lighter ones, such as silicon and oxygen are in the mantle and crust. This means the heavier elements, like gold (did you know that gold is nearly twice as heavy as lead, and nearly three times as heavy as iron?), are likely to be more abundant in the core. In fact, the Earth's core might be an easier place to get the gold than other planets[4]. The cost of mining gold, or anything else, from other planets is currently prohibitive. Also, please note that gold has little intrinsic value; its chief value comes indirectly from its rarity.
To answer your question, gold is likely not evenly distributed among the planets, even if they initially started out relatively evenly. In fact, gold isn't even likely to be distributed evenly within one planet, with more gold being available in deeper layers, outside of reach with our current technology.
I hope this answers your question.
Regards,
Bart
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