How many years will it be before Pluto moves outside the orbit of Neptune?

Hi Mike,

>What marks the end of the protoplanet stage?

There's no clear-cut boundary between "protoplanet" and "planet".
Even today the Earth is growing very very slowly as meteorites, mostly
as small as dust grains, fall to the surface out of the space between
the planets.

Recent models of giant planet formation suggest a rocky core forms
first. When the core grows large enough, it suddenly pulls in gas
>from the protostellar cloud around it. If that model is correct, you
could say that while it's still mostly rocky, it's a
"proto-giant-planet" and when it's become mostly gaseous it's a
newborn giant planet.

>How many years will it be before Pluto moves outside the orbit of Neptune?

>From the "Tour of the Nine Planets" entry for Pluto, on the Web at
SEDS' home page http://www.seds.org:

"Pluto's orbit is highly eccentric. At times it is closer to the Sun
than Neptune (it has been so since 1979 and will continue until 1999)"

Regards,
-Neal.

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