[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

[Juramike]

Objects smaller than the Sun occupy a multidimensional continuum of values. Level of differentiation, atmosphere, size, distance from parent star, crustal materials, past/current geologic processes, etc. Choose the right dimensions, and there will be a unique place for everything: Io, Pluto, Eris - everything could get a coordinate.

All of the objects could be plotted in multidimensional space and subjected to cladistic analysis to draw up clusters of objects. But when you define up the clusters, you may end up drawing up borders that may not make much sense in the big scheme of things. And some of these might end up being arbitrary.

For instance, my own personal level of "interesting objects" [crustally differentiated objects with a solid surface]: Mercury, Venus, Earth, Moon, Mars, Ceres, Io, Europa, Ganymede, Titan, Triton, Pluto.

My list of "preferred interesting objects" [crustally differentiated objects which may have had "recent" geological activity] includes: Venus, Earth, Mars, Io, Europa, Ganymede, Triton, Pluto

And my arbitrary list of "most preferred interesting objects" [crustally differentiated objects which may have had recent geological activity and have an atmosphere and that we've taken pictures of the surface]: Venus, Earth, Mars, Titan

All this demonstrates that the groupings and definitions we give objects are arbitrary in the eye of the definer. (The data itself is not, but how the data is grouped is.)



Pluto will still be Pluto whether we call it a "planet" or not.

Whether Pluto is a "planet" or not, for me, is an uninteresting discussion.

A much more intereseting discussion would try to answer:
How is Pluto similar/different from Earth?
How is Pluto similar/different from Titan?

Those are the questions I get excited about.

-Mike

[Alan Stern]

Objects smaller than the Sun occupy a multidimensional continuum of values. Level of differentiation, atmosphere, size, distance from parent star, crustal materials, past/current geologic processes, etc. Choose the right dimensions, and there will be a unique place for everything: Io, Pluto, Eris - everything could get a coordinate.

All of the objects could be plotted in multidimensional space and subjected to cladistic analysis to draw up clusters of objects. But when you define up the clusters, you may end up drawing up borders that may not make much sense in the big scheme of things. And some of these might end up being arbitrary.

For instance, my own personal level of "interesting objects" [crustally differentiated objects with a solid surface]: Mercury, Venus, Earth, Moon, Mars, Ceres, Io, Europa, Ganymede, Titan, Triton, Pluto.

My list of "preferred interesting objects" [crustally differentiated objects which may have had "recent" geological activity] includes: Venus, Earth, Mars, Io, Europa, Ganymede, Triton, Pluto

And my arbitrary list of "most preferred interesting objects" [crustally differentiated objects which may have had recent geological activity and have an atmosphere and that we've taken pictures of the surface]: Venus, Earth, Mars, Titan

All this demonstrates that the groupings and definitions we give objects are arbitrary in the eye of the definer. (The data itself is not, but how the data is grouped is.)



Pluto will still be Pluto whether we call it a "planet" or not.

Whether Pluto is a "planet" or not, for me, is an uninteresting discussion.

A much more intereseting discussion would try to answer:
How is Pluto similar/different from Earth?
How is Pluto similar/different from Titan?

Those are the questions I get excited about.

-Mike

Mike-

I agree with the high "interest factor" in your two questions just above, start a thread! But regarding planet definition, I hope the the topic (for everyone, not just this forum) needs to move from a "contest" over Pluto (let it fall where it may) to a rational one about planet categorization in general. Putting Pluto in the middle of it clouds the arguments, with people claiming there are issues of sentimentality, American pride, etc.; it distracts attention from the important issue of getting a workable definition and categorization of planets. Sykes and others (not sure about Tyson) have accepted this point and will be echoing it at GPD later this week.

Are you going to be at GDP?

-Alan