Is that the right term for a planet of small stature?

From NASA site: "A Hubble Space Telescope image of Pluto and its moons. Charon is the largest moon close to Pluto. The other three bright dots are smaller moons discovered in 2005 and 2011." Apparently, we still don't have a close-up.

Well, that was exciting. (Ralph Hightower will like this; he’s into space stuff.) I just got a reply from the Hubble via Twitter.

Having seen this:

Astronomers using @NASA_Hubblediscover another moon orbiting dwarf planet #Pluto! http://t.co/PubN0ov

… I naturally asked, “Does that make it a planet again?” I had read right past the “dwarf planet” reference, because I didn’t know what that was.

@NASA_Hubble wrote back to me, “Not quite,” and urged me to “See Resolutions 5A and 6A.” Which I did. To share:

RESOLUTION 5A
The IAU therefore resolves that planets and other bodies in our Solar System, except
satellites, be defined into three distinct categories in the following way:
(1) A “planet”
1
is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for
its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium
(nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient
mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic
equilibrium (nearly round) shape
2
, (c) has not cleared the neighbourhood around its orbit, and
(d) is not a satellite.
(3) All other objects
3
, except satellites, orbiting the Sun shall be referred to collectively as
“Small Solar-System Bodies”.
IAU Resolution: Pluto
RESOLUTION 6A
The IAU further resolves:
Pluto is a “dwarf planet” by the above definition and is recognized as the prototype of a new
category of trans-Neptunian objects.
1

RESOLUTION 5AThe IAU therefore resolves that planets and other bodies in our Solar System, exceptsatellites, be defined into three distinct categories in the following way:(1) A “planet”1is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass forits self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium(nearly round) shape, and (c) has cleared the neighbourhood around its orbit.(2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficientmass for its self-gravity to overcome rigid body forces so that it assumes a hydrostaticequilibrium (nearly round) shape2, (c) has not cleared the neighbourhood around its orbit, and(d) is not a satellite.(3) All other objects3, except satellites, orbiting the Sun shall be referred to collectively as“Small Solar-System Bodies”.IAU Resolution: PlutoRESOLUTION 6AThe IAU further resolves:Pluto is a “dwarf planet” by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.1

Well, that’s better than nothing. Not that we’ve always given actual human dwarfs much respect on this planet, but I suppose being some kind of planet is better than nothing. WAY better than being just a “trans-Neptunian object.”

5 thoughts on “Is that the right term for a planet of small stature?”

  1. Steven Davis

    I guess it depends on what Obama says, he’s said no to the space program so he’ll probably not bother with the whole Pluto planet thing.

  2. tim

    He said no to the Orion program as previously conceived, as expensive & inefficient. He said no to the big government institution (Orion) over the private sector solution he is proposing (Space-x). BTW, its an American company, which is proposing to be 10 times as efficient in cost versus the government-built system based on its cost estimates. By comparison, the shuttle program was life-cycle estimated to cost 12 Billion over 12 years. Its actual cost ended up being twice that. And it never met the initial goal of fast, cheap reusable vehicle. It was a hand-crafted kluge, that proved highly delicate. I love the shuttle. It made me proud and struck my imagination. It was not a good long-term solution to manned spaceflight.

  3. Brad

    The trouble with private space flight is that, no matter how efficient it is, it will never be big enough to do anything cool like land on Mars.

    At least, not any time soon. Gimme a big ol’ hairy, panicky “the Commies are gonna be dropping nukes on us like rocks from a highway overpass” kind of national priority, so we can get going. I’m tired of waiting.

  4. tim

    Look… I LOVE our government space missions. Its one of the best things we do. It may well be that only the US, or an international coalition can do Mars. Elon Musk is making plans to take SpaceX to Mars in 20 years. I think thats ahead of NASA’s timetable. BTW, I have a pretty strong case that the Space Race ended on Christmas Eve, 1968.

  5. Steve Gordy

    Now seems to be the time for a lot of cleaning-up. I heard on the news this a.m. that NASA is harassing astronaut Edgar Mitchell to return a 16 mm movie camera he took to the moon – on Apollo XIV, which made the trip in January, 1971 (I got to see this launch live).

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