because the dust becomes thinner the further we travel towards the outer edges of our own

英语比较级中有这样一种用法，即"the + 比较级， the +比较级"，翻译为"越....,越..." 例如：The more you practice , the better your spoken English will become. 你练习得越多，你的英语口语就会变得越好。你所写的句子，正规来讲，应该是这样的：The further we travel towards the outer edges of our own solar system, the thinner the dust becomes.