AAS DPS 2008: Pluto
They're still arguing the 'is Pluto a planet' question. I've got to be honest: without much of a stake in the debate (i.e., not being a PI to an icy planet that became a dwarf one) I can't muster that much energy for it. But I'd still be scared of arguing with Hal Levison, who spoke earlier this weekend at a special session on the question.
Hal works at Southwest Research Institute in Colorado, and is an expert on solar system dynamics, and the processes by which little planetesimal pieces coagulate into bigger bodies. He's a big body himself: burly, bearded and boom-voiced, dressed in baggy blue jeans and boots. Eyes flashing, he could be a viking without a helmet. He thinks the whole Pluto debate is kind of absurd. Just look at the distribution, he says. (A nice graphic that Hal refers to, courtesy Cassini scientist John Spencer, after the jump). In the graphic, which shows body size on the y-axis and orbital radius on the x-axis – in logarithmic scale – eight things clearly stand out. They are the planets. Everything else is part of a distribution: asteroids, trojans, KBOs, etc. It's obvious.
If you go with a size definition, based on this roundness, his daughter will have to memorize 1,000 planets. He doesn't like that. “Also, the mnemonic would really suck.” He wishes people wouldn't associate non-planets with lesser scientific importance. He's personally most interested in smallish Kuiper Belt Objects. “These guys,” he says, pointing to the small bodies, “including Pluto, are the coolest things in the solar system. I don't care what people say.”
I'm glad the big guy is looking out for the little guy.
Comments
At the beginning of the topic all person say is pluto planet ı think we have a lot of planet in the world we dont know beetwen our world how much planet maybe they are to much smaller than our world where we know
Posted by: evden eve nakliyat | October 15, 2008 12:08 AM
I met Hal at the Great Planet Debate in Laurel, MD; he's actually a really nice guy, and I had/have no fear of arguing with him, as I totally disagree with his dynamical planet definition--as do many professional astronomers. Your implication that Dr. Stern is motivated by anything other than scientific concerns is very unfair. The real problem is the IAU definition that states dwarf planets are not planets at all. If this were reversed, much of the argument would dissipate. In a 2000 article, Stern and Levison talk about two classes of planets--the big, dynamically dominant "uber-planets" and the small, "unter-planets." While they distinguish between the two categories, they never claim the "unter-planets" are not planets. There is a strong case to be made that any non-self luminous spheroidal object orbiting a star is a planet. Objects in hydrostatic equilibrium are fundamentally different than shapeless asteroids, as they are differentiated and have the same geological processes as planets. Why not keep the term planet broad and distinguish the different types through using subcategories? Memorization and the issue of the number of planets in our solar system are not important. We don't limit the number of elements in the periodic table because there are too many for kids to memorize. Pluto, Eris, Haumea, and Makemake are both planets and Kuiper Belt Objects. Most KBOs are not large enough to have attained hydrostatic equilibrium and so will not fall into this dual category. However, using a flawed definition that totally ignores what an object is and defines it solely by where it is is inaccurate and does a disservice by blurring the very important distinction between shapeless, inert asteroids and those large enough to have the same geological processes as the major planets. The IAU definition is majorly flawed, and I for one hope to see this debate continue for a long time. We likely will find a lot of answers when New Horizons gets to Pluto in 2015.
Posted by: Laurel Kornfeld | October 15, 2008 06:16 AM
I met Hal at the Great Planet Debate in Laurel, MD; he’s actually a really nice guy, and I had/have no fear of arguing with him, as I totally disagree with his dynamical planet definition–as do many professional astronomers. …
Posted by: I met Hal at the Great Planet | October 29, 2008 04:09 PM
I am an Earth scientist, and one who has NOT followed this debate in any detail (so maybe this has been suggested).
To me, a planet should/could be defined as a body big enough to have undergone internal chemical differentiation(core/mantle/crust/atmosphere on Earth). By this definition, the 8 'main' planets of our system are planets and Pluto is not a planet. Our Moon is a planet (captured by the Earth). Maybe some of the 'moons' around the outer gas planets are also captured planets.
So shoot me down now!
Posted by: hugh rice | November 5, 2008 12:12 PM
i think, after pluto, there is other planet, but maybe our system haven't detected it yet.
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