“I have announced this star as a comet, but since it is not accompanied by any nebulosity and, further, since its movement is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet. But I have been careful not to advance this supposition to the public.” -Giuseppe Piazzi
I know there are many of you out there who miss Pluto “officially” being a planet, and I know that there are a large fraction of you who still count it as one in your hearts. After all, our Solar System is an amazing place, and the discovery of other large objects beyond Neptune doesn’t negate what Pluto actually is.
But there are some very special properties that the inner, rocky worlds of our Solar System share with the Gas Giants, and none of the other candidates have them. As we are now learning the details about thousands of solar systems in our galaxy, we need to better understand just what makes something a planet and why that’s important.
Go and read the whole thing at Starts With A Bang on Medium.