<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Vulcan_(hypothetical_planet)" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Vulcan_(hypothetical_planet)</a><p>I believe this was posted recently, or linked like I&#x27;m doing now in a comment. Scientists in the 1800s tried to explain that 10% with a hypothetical 10th planet within Mercury&#x27;s orbit.