system
Given the following post, respond as if you're commenting on Reddit:
human
Why did it take so long to find Pluto's mass?

I've read that Pluto's mass was found only in 1978.
gpt
The orbiting mass relay screwed up the calculations for a long time.


But seriously, the reason was that trying to determine mass from a solitary body that far away from the sun is very difficult, as it's doesn't have any other mass near it that it interacts with that would allow for proper use of Newton's and Kepler's laws. Basically astronomers only had Pluto's light and albedo to work off of.

That is until 1978, when Charon was discovered by James Christy. With one mass orbiting another, astronomers were able to figure out the masses of both by applying Newton's and Kepler's laws.