[X] My Assistant

[JRehling]

Probably some perfect "grand tour" type alignment, where each spacecraft-planet encounter is as close-in to the planet as possible for a departure trajectory that's approximately tangent to the planet's orbit or as close to tangent as possible.

Eris is also well off of the ecliptic at present (and for a long time coming). I doubt that keeping things in the ecliptic for three flybys then counting on Neptune to provide all of the work to acquire a high inclination is feasible. Maybe a Jupiter-Saturn combo could do it, assuming the rings weren't a problem.

That would actually be a scenario that would unfold fairly often.

Uranus is actually in a pretty good position right now for an assist to Eris, but it'll soon move out of that good position and not come back for 8 decades. Neptune, however, is moving into position, but again, Neptune can't bend the path down in very good proportion to Jupiter's bending it out.

In only 230 years or so, Eris will come within 40 AU of the Sun. Let's plan on an Eris Orbiter/Lander then. Start the buzz now.

[Alan Stern]

You probably already know about The Great Planet Debate meeting coming this week near DC, if not, see:
gpd.jhuapl.edu.

To register for Great Planet Debate conference web participation, click: http://tinyurl.com/6xcqec
Watch the talks and debate on line!

-Alan

[Floyd]

"Biologists classify animals" is a good one to look at. First of all, they do so with controversy and alternate approaches of many kinds.

A few comments from a microbiologist:
I think there is some confusion between scientific research and authority to define scientific terms.
Progress in science results from experiments where data is generated and analyzed. Hard science deals with measurements and validating hypotheses. However, every field need a vocabulary to communicate within the speciality and to the broader community. The assigning of objects (molecules, bacteria, planets) to groupings has more to do with esthetics than science (but should be scientifically informed). Determining the mass of a virus or planet is a scientific task which we can do with great precision. Coming up with definitions or names depends on building consensus (no standard error bars) among scientists in the field.
In biology, we can determine the evolutionary distance between living organisms by sequencing the DNA for the small ribosomal RNA and counting the mismatches in the aligned sequences. This measurable information is helping to define the grouping of all living organisms (Kingdom, Phylum, Order ...Genus, Species). In microbiology, an international committee validates all names, but microbiologists are free to ignore approved names for what they think is correct. Usage and consensus eventually rule. The scientists responsible for naming grouping and objects in biology do so only for their area of expertise. Zoologists name animals, Botanist name plants and microbiologist name bacteria and archaea. Seems logical to me for planetary scientist to come up with the definition of a planet. Its helpful if the scientific definition does not differ too much from common understanding or general usage (but often it does for good reason).
The IAU definition seem to flunk the esthetics test as well as the consensus of people in the field test.
-Floyd

[JRehling]

All of these examples are useful for setting up a classification of Classifications.

"Continent" has three useful candidate definitions.

1) The large, nearly-contiguous landmasses evident on globes. Ignoring the isthmi (there's a word you hadn't seen yet this decade) of Suez and Panama, you have North America, South America, Australia, Africa, Antarctica, and Eurasia. If you're a traveler -- an extreme mountaineer, perhaps -- it's quite useful. Or for setting up international fishing domains or somesuch.

2) The landmasses known to the ancients, augmented with the four discovered later. Same as above, but with Europe and Asia separated.

3) The landmasses whose tectonic plates whose areas are centrally or primarily land instead of sea. That puts India and Arabia on the list, with Eurasia grouping Europe and Asia.

One thing I find obnoxious about the whole planet thing is the presumption that because the people using #3 are scientists that their definition is "The" definition, leaving the PhDs to "tut tut" and stroke their beards kindly in derision, and leaving museum docents to tell the child who "knows" about #3 that he/she is correct and leaving the poor, misinformed kids brought up on literature and culture to sulk in their incorrectness. It's so wrong. It's not only factually wrong; it's immoral.

No one should begrudge geologists the use of #3. It's great for what they're doing. It's useful. It's a happy world where they use it for their purposes without feeling like silly Virgil and the whole Classics department are ignorant because they use #2 and brow-beating the elementary schools of the world into adopting #3 because it's a fact. Although it's great if geology teaches that #3 is useful -- for geology.

Now if scientists had stumbled upon a scientifically useful definition of planet and kept it to the scientific domain without sending out a memo that the silly people are incorrect and ignorant, that would have been fine. But what has happened has deviated from that in three unfortunate ways:

1) The memo has been sent out. Kids who use that definition are told they're correct. Kids who don't aren't.
2) The definition was almost painstakingly crafted to be useless to scientists! Far worse than if geologists had brow-beaten the geographers into submission, this is a case where the scientists have created a definition that ONLY has relevance on the other side of the boundary. The scientists themselves have no use for it.
3) Per my observation of the books I have (unfortunately) bought and taken into my own house, actual scientific content that was present in earlier editions has been eliminated and replaced with this fad. Whatever meager information was once there about Pluto, it's now been cut in half. Instead of telling them that we can use the light from Pluto to tell that it's made of ice, we're telling them something that isn't science.

[Greg Hullender]

One thing I find obnoxious about the whole planet thing is the presumption that because the people using #3 are scientists that their definition is "The" definition, leaving the PhDs to "tut tut" and stroke their beards kindly in derision, and leaving museum docents to tell the child who "knows" about #3 that he/she is correct and leaving the poor, misinformed kids brought up on literature and culture to sulk in their incorrectness. It's so wrong. It's not only factually wrong; it's immoral.

I don't see this, though. There are countless popular terms that don't match the scientific ones, and it doesn't bother anyone. An architect friend once told me that what I call "asphalt" he calls "asphaltic cement," and that for builders, asphalt is just one of the ingredients. Matters a lot if you're a builder, but the general public doesn't care. It's cute to know that a tomato is technically a fruit, not a vegetable, but only a botanist cares. Kids learn about it, but they don't go correcting their parents about it.

Or consider a rock that falls from space. In space, it's a "meteroid" (and presumably an object a Planetary Scientist might want to study), but once it hits the atmosphere, it becomes a "meteor" (perhaps of interest to Meterorologists) :-) and when it hits the ground, it's a meterorite (and belongs to Geology). Normal folks don't know these distinctions (if I've even got them right myself) and they don't care. They just call everything a meteor. A bright kid might correct his elders in a museum -- "That's not a meteor, dad; it's a meteorite!" -- but they just chuckle.

I can't for a minute see how any of this rises to the level of a moral issue. And kids "brought up on literature and culture" simply say "who cares?" They never give the wrong answer in the first place.

--Greg