Category Archives: dwarf planets

astronomy news, dwarf planets, Plutoid

You’re Not Just a Dwarf Planet…

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You’re a Plutoid

After two years of what must have been grueling discussion, the International Astronomical Union has decided that things that are like Pluto (which used to be defined as a planet) are now going to be called “Plutoids” as long as they orbit at or beyond the orbit of Neptune. Dwarf planets (as a small-body definition), as you may recall, was an outcome of the 2006 IAU meeting, when it was decided that we needed a new category for worlds that aren’t quite planets, but are bigger than asteroids. The name plutoid for a specific subset of dwarf planets was proposed by the members of the IAU Committee on Small Body Nomenclature (CSBN), accepted by the Board of Division III, by the IAU Working Group for Planetary System Nomenclature (WGPSN) and approved by the IAU Executive Committee at its recent meeting in Oslo, Norway.

Two Plutoids: Pluto (shown with its companion Charon) and Eris (with Dysnomia)

So, what are the characteristics of Plutoids? They have to be celestial bodies in orbit around the Sun at a distance greater than that of Neptune. They must have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape. And, they haven’t cleared the neighborhood (of debris) around their orbit. So, Pluto and Eris fit this definition, and scientists expect more small worlds like them to be found as astronomers keep finding them out the great beyond.

By this definition, the dwarf planet Ceres is NOT a Plutoid, but it’s still a dwarf planet. This is because its orbit is within the asteroid belt and not transneptunian.

dwarf planets, moons, Pluto, solar system exploration

Cold and Then Some

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Cold, and then Some

Up until a couple of days ago we were shivering under some pretty cold temps up here in New England. The other night we took the trash out and it was about 10 below zero (F)—cold enough to literally take your breath away. The sky was quite clear that night, and the stars were stunningly beautiful. Mars was like a red beacon…The next day I walked out to get the mail and noticed the ice in the driveway. It reminded me of pictures I’d seen of ice fields on the worlds of the outer solar system. Out there ice doesn’t so much melt off the surfaces of those worlds, but it sublimates—it turns from ice crystals into a gas without going through that pesky liquid phase we see here on Earth.

Oh, there is liquid water out there at the outer worlds. At least, that’s the working hypothesis deduced from various observations. And, how else do you explain what looks like deposits of fresh ice that have somehow oozed up through cracks on the surfaces of places like Enceladus, Europa and Pluto’s moon Charon? It’s only a matter of time before the existence of all those cold oceans are confirmed. And, when I read about them, I can certainly sympathize with the idea of cold—especially after the bitterly cold weather we had last week. However, I am reminded that 10 below zero here on Earth would be a pretty warm day on Mars or Enceladus or Tethys or Pluto or Charon— so we have it pretty good here at home.

Speaking of cold and ice and outer solar system, here’s the latest installment of my ongoing vodcast series. It features an observation made at Gemini Observatory that I wrote about a few months ago, and an image I worked on with the PR folks at Gemini. Come on—let’s go visit some ice worlds!


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