Sets the Relative Scale of the Solar System. The Absolute Scale is still unknown and the most remote known planet is:
The Discovery of Uranus in 1781.
Thomas Henderson and the first measurement of stellar parallax in 1839 This is a big deal because it now shows that the distance to the nearest stars is extremely large. This means that the stars are powered by an "unknown" source of energy.
Well if the distance to the nearest stars was this large, how far away were the objects that Messier was finding: