Question: > 
> He crashed the car into a wreck where the police inspected the debris.
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I am assuming where is a pronoun here. The question is whether the word that precede where must be a location. From most examples, it seems that if it's a pronoun it must refer to a noun preceding it unless it's at the start of a sentence. Is this the case? Also, note that wreck refers to the state and not the location; hence, the question.

Answer: 
For clarity, I would say *more eccentric than planet Earth's*, the possessive clarifying that the orbit of Earth is what is discussed. Otherwise the comparison is between orbits and Earth as a planet, which may be the source of the error.
The sentence appears to compare "orbits" with "planet Earth". This is probably not what the writer intended. Instead they intended to compare "orbits of comets" with "the orbit of the planet Earth".

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> The orbits of comets are more eccentric than that of planet Earth...
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But as noted in a comment, native speakers are not robots, and we could follow the intended meaning perfectly well. There is no need to mark this as an error. Similar expressions occur frequently without causing problems.