The Great Planet Debate conference, August 2008 - Washington DC Options

[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

[djellison]

Nobody can change what these planets 'are'.

But they can try and come up with a better way of categorizing them - the current system is utterly broken (and that's coming from someone who doesn't care if Pluto is a planet or not,I just want a definition that makes sense)

Doug

[Greg Hullender]

But they can try and come up with a better way of categorizing them - the current system is utterly broken (and that's coming from someone who doesn't care if Pluto is a planet or not,I just want a definition that makes sense)

I'm still liking Mike Brown's thinking on the matter:

http://www.mikebrownsplanets.com/ (scroll down to "Ground rules for debating the definition of 'planet'")

He says he personally considers the debate closed, but since we don't seem to be able to move on, he proposes some rules for the discussion.

There's a lot of good stuff here, but this struck me as new information:

Misleading statements about the previous vote should also be disallowed. Yes, the whole IAU procedure was a bit mucked up, but the results would likely have been the same no matter who was in the room at the time. Surveys done after the IAU vote – yes there were some! – showed that astronomers by a large number thought that the 8 planets definition was a good one. So complaining about the IAU vote gets you the label of “misinformed about how most astronomers think."

I thought that was a particularly strong claim. I wonder who does those surveys? :-)

--Greg

[Alan Stern]

I'd sure like to know too. The only one I know of is the Sykes-Stern petition, which in 48 hours after being introduced gained 300+ signatories who were displeased with the IAU vote.

Brown's assertion that the vote "would" have been the same is unsupported.

Worse, voting in science is about the worst way one can go: can you imagine if there were voting on evolution, global change, etc.? Voting is antithetical to science, which works by archieving consensus based on which models best fit an ever expanding base of data.

Anyway, The GPD later this week in Maryland will feature debate and no votes. Come to the meeting or tune in if you can't and are interested.

-Alan

I'm still liking Mike Brown's thinking on the matter:

http://www.mikebrownsplanets.com/ (scroll down to "Ground rules for debating the definition of 'planet'")

He says he personally considers the debate closed, but since we don't seem to be able to move on, he proposes some rules for the discussion.

There's a lot of good stuff here, but this struck me as new information:



I thought that was a particularly strong claim. I wonder who does those surveys? :-)

--Greg

[Mongo]

Worse, voting in science is about the worst way one can go: can you imagine if there were voting on evolution, global change, etc.? Voting is antithetical to science, which works by archieving consensus based on which models best fit an ever expanding base of data.

I agree. However, in this case the debate is over terminology, not science. In my own opinion (for what it is worth), the term 'planet' is obsolete and should be retired. I would go with several sets of terms for each type of object: a set of terms for composition -- 'gas giant', 'ice giant', 'terrestrial' and 'ice dwarf'; a set of terms for orbital status -- orbiting the Sun, orbiting another body that in turn orbits the Sun, or in a mean-motion resonance with a more massive Sun-orbiting body; and a set of terms for gravitational self-rounding (including non-typical objects like 2003 EL61) -- fully gravitationally relaxed, partially relaxed, unrelaxed.

So Pluto would be a fully gravitationally relaxed ice dwarf in a mean-motion resonance with a more massive Sun-orbiting object.

Luna would be a fully gravitationally relaxed terrestrial orbiting a more massive Sun-orbiting object.

Vesta would be a partially gravitationally relaxed terrestrial orbiting the Sun.

And so on.

[Alan Stern]

I agree. However, in this case the debate is over terminology, not science. In my own opinion (for what it is worth), the term 'planet' is obsolete and should be retired. I would go with several sets of terms for each type of object: a set of terms for composition -- 'gas giant', 'ice giant', 'terrestrial' and 'ice dwarf'; a set of terms for orbital status -- orbiting the Sun, orbiting another body that in turn orbits the Sun, or in a mean-motion resonance with a more massive Sun-orbiting body; and a set of terms for gravitational self-rounding (including non-typical objects like 2003 EL61) -- fully gravitationally relaxed, partially relaxed, unrelaxed.

So Pluto would be a fully gravitationally relaxed ice dwarf in a mean-motion resonance with a more massive Sun-orbiting object.

Luna would be a fully gravitationally relaxed terrestrial orbiting a more massive Sun-orbiting object.

Vesta would be a partially gravitationally relaxed terrestrial orbiting the Sun.

And so on.

Mongo-

Since planetary science is a field and planetary scientists have a profession, I do not think we can or want to retire the term which planets. Instead, our field and our profession need to come to a consensus on what we, the practitioners, consider to be planets vs. smaller and vs. larger things. That astronomers hijacked this process is about equivalent to brain surgeons, rather than cardiologists, deciding where the dividing lines between veins, arteries, and capillaries are, and the public/press following along because "they are all doctors, after all."

As to Hungry4Info's question, no one really has the authority to change the status of Pluto or other bodies. Science doesn't work by such decrees-- it works by finding the best solution that fits the data, which is fundamentally about achieving consensus, not votes or decrees.

Hope this helps.

-Alan

[Greg Hullender]

Since planetary science is a field and planetary scientists have a profession, I do not think we can or want to retire the term which planets.

That's actually a very powerful argument I haven't really heard before -- that the scientific definition of planet should correspond to "worlds that have geology," because that's what Planetary Scientists study. That means, though, that our Solar System has about thirty planets, since this includes our moon and about seventeen other moons on top of the magic eight and the four dwarves. (Or am I completely confused? You're the real Planetary Scientist here.) :-)

Sometimes it does seem that all the counterarguments to this definition really boil down to "but what will we tell the children?" A fair point could be made that the definition should serve scientists -- not school kids -- given that there are in fact scientists to whom it's useful.

--Greg