For the last time, Pluto is still there
I’ve been wrapping up some selected bits of gravitation with some students. I do gravitation right before Christmas break, and any student that was out of class for significant time before the holiday needs to work on this material now.
I got into a discussion about the solar system with a student and a fellow faculty member yesterday, and I used Pluto as an example of a planet with a large orbital period (time to go around the Sun).
At the mere mention of Pluto I was greeted with two sad faces. “Poor Pluto,” they said.
I replied, “But nothing’s different! Pluto is still there! We just know more about it now!”
Pluto is still there. It’s still going around the Sun. Its orbit didn’t change, its characteristics didn’t change, its three moons didn’t change, nothing changed. Scientists sitting in a meeting can’t modify the objects in the solar system on a whim.
For the entire first half of the nineteenth century, astronomers classified four asteroids (1 Ceres, 2 Pallas, 3 Juno, and 4 Vesta) as planets too. Discovered between 1801 and 1807, they became visible to us as our observational tools (i.e., telescopes) improved. If we had lived in the early nineteenth century, Many Very Educated Men Could Prove Just Visible Junk Shines Uniformly.
But all this changed on December 8, 1845, when K. L. Hencke discovered 5 Astraea. A fifth asteroid? Who would have thought! By the end of 1850, a total of 13 asteroids were known. By the end of 1860, there were 62 known. By the end of 1870, 112. Currently there are more than 173,000 identified asteroids, most within the designated asteroid belt. There are also more out there — as our tools allow us to see more clearly, we learn more about what is around us.
The anatomy teacher listening to our exchange replied, “But I want to know everything. I can’t stand it when we don’t know something.”
What makes science great is that we don’t know.
Our classifications and groupings of things and ideas needs to change as we continue to observe. This makes many people uncomfortable, students and teachers.
Science is a process, not a body of knowledge. We discover new things by looking at everything we can see, and finding the connections between new observations and old. Sometimes we need to change our classifications as a result of new information. It happened to Pluto and Ceres and will happen to other objects.
I want to know everything, but the moment we know everything, science will be over. What’s more exciting, watching an exciting game or the game’s highlight reel two weeks later?
Tags: asteroids, ceres, gravitation, hencke, juno, pallas, physics, pluto, vesta
January 29th, 2008 at 4:33 am
…poor Pluto.
We don’t really know more about it, though, do we? I mean, we must’ve known its orbit was relatively eccentric and it was really tiny before we decided to stop calling it a planet (an issue about which I do NOT recall voting, thank you). Nothing really changed, except a panel of scientists decreed that Pluto isn’t a planet to avoid opening a Pandora’s Box of asteroids being called planets because Pluto set a precedent.
I forget where I’m going with this.