That distant world called Pluto has surprised astronomers again, yielding up yet another moon. Pluto’s largest moon is Charon and was discovered in 1978. Two more — Nix and Hydra — were found in 2005. The new one, called P4 (for now), is quite small, somewhere between 13 to 34 kilometers across, and small enough that it was probably missed in earlier images of the system taken by Hubble Space Telescope. This latest HST image was taken as part of a search for ring material around the distant dwarf planet, in support of the New Horizons mission, which is en route to Pluto.
So, how would Pluto, itself a small world like many others in the outer solar system, get moons? The current thinking is that a collision between Pluto and another world early in the history of the solar system would have flung material out into orbit. Eventually, the pieces and parts would have coalesced back together, forming the family of moons we see today.
When I read this story, the first things I wondered were “Why search for rings around Pluto?” and “Where would the material for Plutonian ringlets come from?” A long-ago collision would have provided material for rings, but by now, that material would have been cleared away or coalesced into moons, such as Nix, Hydra, P4 (and maybe even Charon?). To maintain a ring system, you need a constant source of material being tossed out to space. At Pluto, that source may well be material “chipped away” from the icy surface by the impacts of tiny micrometeoroids. That would provide chips of ice to form a faint, thin ring. If it exists, it hasn’t yet been detected. But, HST would be the best instrument we have at this time to find the ring. Once New Horizons gets there, it may well “see” the ring, if it exists.
I like it when HST finds things like this. It’s a continuing reminder that the venerable telescope has a lot of life in it yet; and will keep surprising astronomers with new finds.
So, I’m on the distribution for a listserv that includes a number people who are involved in public outreach in astronomy. Most of the time, the discussions are aimed at things that concern such professionals: astronomy news, tips on lecturing, what materials are available, who’s showing/talking about what, meeting announcements and that sort of thing. But, occasionally there are topics that crop up that cause the same reaction you’d see if you tossed red meat to a group of starving wolves. The “Pluto is/is not a Planet” topic is one of them.
Most of us just roll our eyes and hit “delete” or “next” when that topic comes up. This is because the same folks rehash the same arguments over and over again. It gets tedious and nobody ever wins. In fact, everybody loses because the list gets taken up with the circular arguments and exclamation points for a while and many of us stop reading or posting to it until the flames die down. I’m not saying we shouldn’t have the discussion, but that maybe the topic is just not going to be solved by yelling and insisting that laws were broken and children are being hurt deeply because Pluto isn’t a planet any more, etc, etc. ad nauseum.
An artist’s conception of Charon (with Pluto in the background) against the backdrop of the Milky Way. The plumes and brighter spots depicted at left on Charon are thought to be created as water (with some ammonia hydrate mixed in) “erupts” from deep beneath the surface. The material sprays out through cracks in the icy crust, immediately freezes and snows crystalline ice down onto the surface, creating a water-ammonia hydrate ice field. Such fields were detected and studied using the near-infrared imager on Gemini North. (This composite image includes Pluto and Charon models (enhanced), courtesy of Software Bisque. www.seeker3d.com, with plumes and ice fields added by Mark C. Petersen, Loch Ness Productions. Star field from DigitalSky 2, courtesy Sky-Skan, Inc.)
Pluto is a planet. Better than that, it’s a special case of planet called dwarf planet. That’s pretty much the take-away message from the IAU vote of a few years ago. There’s a lot of other stuff in the current definition that IAU posted about how we define planets (and you can read it here). People LOVE to argue about the rest of the definition and how it might be used to exclude Earth, and how the vote wasn’t fair and yadda yadda yadda. But, the essential message here is that Pluto and worlds like it are now deemed dwarf planets.
This makes perfect sense to me. We have dwarf galaxies. We have brown dwarf objects sitting in the cellar of the star classification schema that nobody would dream of saying fit into the canonical definition of “star”. We just accepted that one and moved right on to study these BDs and figure out where they fit in the evolutionary schema of the cosmos.
So, why not dwarf planets? They certainly occupy a special shelf in the solar system bodies collection. Science is partly about classifying objects, and so what the IAU did (and I do understand that it doesn’t sit well with some people) is to refine the classification — just the same way we do with other sets of objects. The finer the classification, the more easily we can define the things we see and — THIS IS IMPORTANT — understand their origins, evolution, and future. This is all part of science. The definition is merely the name we plaster on it that tells us, in a sort of nice shorthand, that “this object is thus and such, and it did this and that, and it will end up as one of those.”
I know this isn’t enough to keep the wolves from continuing to tear away at the dead horse of what they think is a bad decision by the IAU. There’s no pleasing some people until you finally give up and say, “Okay, you’re right. All the rest of us are wrong, the whole world is wrong, only your opinion counts in the marketplace of ideas, so can we get back to work now?”
But, think about this: the definition of planet, and Pluto in particular, is a teachable moment. It’s a lesson in how scientists classify things and how we come up with the schemas that we use to identify and understand things in nature. THIS is the lesson that kids (and a lot of adults, apparently) need to learn. It’s not so much the name as what the name stands for. And, it’s not the time or place for a lesson in screeching like a banshee in order to get your point across, or, in the case of some states in the U.S. the time to do silly crap like pass resolutions that Pluto is a Planet. THAT is a colossal waste of time and money, shows students that science is somehow governed by political laws, and makes about as much sense as the legislative body deciding to declare that Pi is equal to 3 or that from henceforth on, dogs shall be declared cats. Sheesh.
