As for going to Pluto, Summer’s only partly correct, IMHO. We would have gone, but not in our lifetimes. New Horizons had been on the chopping block twice before the probe had been completed. One of the reasons it managed to push through is that Pluto is now entering its winter, and scientists wanted to visit before its atmosphere froze out.

Historically speaking, its been decades between missions to the outer worlds. The Grand Tour of ’77-’89 wasn’t offically planned as such; it was originally a mission to fly by Jupiter and Saturn. Galileo arrived at Jupiter in 1995; Cassini reached Saturn in 2004. There are currently no plans to revisit Uranus and Neptune.

As for JIMS comment about the asterisk, well… with the discovery of Eris, it’s clear that Pluto wasn’t taking steroids, so all the home runs it hit seem to be due to natural athletic skill.

They should just ‘grandfather’ Pluto in, and put an infamous asterisk in future astronomy record books.

Will the definition of a planet change again? Possibly. That’s the good thing about science. At one time an atom was considered indivisible. Now we know better. BTW, Ceres, the asteroid, was once considred a planet back around 1850 and then was demoted as we learned more about the asteroid belt.

Also, I don’t accept the premise that if Pluto wasn’t considered a planet we wouldn’t explore it. NASA, and other agencies, have sent probes to comets, asteroids, moons, and just to collect dust. Basically if it is out there we are going to take a look at it.

With the discovery of more extra-solar planets that don’t behave the way the planets in our solar system do, and how much more scientists are learning from that info, will that mean that that definition going to change again in another 50 years?

Or will they start coming up with different definitions for different solar systems, based on star type or even separating them by near-orbit and far-orbit, or something else that seems arbitrary to most folks?

Besides, I always wanted to see a Pluto expedition drop a few thousand cockroaches on the surface and see how well they survive. Now that it’s not categorized as a planet, that may never happen.

But the jist of it is this: there has been a multi-decade debate on what constitues a planet and for all that time Pluto was one of the primary offenders. It doesn’t look like nor act like the classic 8 planets. As we learn more about the solar system we are finding out that Pluto looks less and less like a planet. So, finally we are trying to come up with a good definition for what a planet is. And Pluto just doesn’t qualify.