New measurements and what they mean

Noted planetary astronomer Mike Brown wrote:

One of the nice things about science is that no matter what you do, eventually, someone is likely to come along and make the same measurement more precisely than you did, and you will get to learn whether you were right or whether you screwed something up. When you screw up, you do so in a very public manner. Everyone knows. You don’t look so good. It’s best to not screw up.

He was reporting a new and more precise measurement of something his team observed five years ago:

… the diameter of Eris is 2336±12 km…..2336 km is well within our 2400±100km that we had estimated. It shows that our very difficult measurement was, in fact, correct.

However, stories like Are Pluto and Eris Twins? and Dwarf Planet Eris, Pluto’s Cosmic Twin are missing the point:

….it’s …. definitely not [true] that Pluto and Eris are “nearly twins” although that is what you will read in the press release that accompanies the paper. In fact, the most important implication [of the new measurement] is that Pluto and Eris – which we used to think of as near twins – are much more different than anyone predicted.

Pluto and Eris are approximately the same size, but that means they have very different densities (because we know Eris is 27% more massive it must also be 27% more dense. That’s a lot)….I am convinced that understanding why Pluto and Eris are so different is one of the keys to understanding the formation of the entire outer solar system. So I find it particularly funny when people say they are twins.

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