QUESTION:
If someone would ask me to explore the surface of Jupiter and let me
choose means of transportation,should I be wrong selecting ....a
boat! ??? 

ANSWER from Jo Pitesky on March 4, 1997:
Jupiter doesn't really have a surface--it's essentially a big ball of (mostly
hydrogen) gas.  Deeper into the planet, the hydrogen becomes liquid, though the
boundary between liquid and gas is gradual.  There might possibly be a rocky
core at the center of the planet, but you'd be squashed like a bug before you
could get there.

But, let's assume that you want some way to explore Jupiter's atmosphere or
interior.  We'll ignore problems like modifying engines so that they can run in
Jupiter's mostly-hydrogen atmosphere, protecting yourself from high radiation
levels and high temperature and pressure, and so forth, and just think about the
best way to get around.  

Cars, trains, even Humvees wouldn't be much help, since there are no surfaces,
let alone roads.  Since there is probably no sharp difference between gaseous
hydrogen and liquid hydrogen (unlike here on Earth, where there's a very
definite point at which sky ends and ocean begins), a boat might not work well. 
Aircraft would have problems with the turbulent winds.

Your best option would be...a balloon.  If you filled up a lightweight balloon
with hydrogen, and then heated the hydrogen (so that it would float--just like
you need a hot-air balloon to float above Earth), you could get a nice tour of
Jupiter by letting the winds take you where they will.

Scientists and engineers are actually considering using balloon craft to explore 
the atmospheres of planets like Jupiter and Venus.