Our Family's Not from Mercury

Our family's not from Mercury.
We've never been to Venus.
I'm certain, if we had been, that
somebody would have seen us.
We've never flown to planet Mars
and never gone to Jupiter.
Suggestions that we've traveled there
could not be any stupider.
We've never stood on Neptune's shores.
We've never circled Saturn1
or seen its lovely colored rings
in their concentric pattern.
We haven't been to Uranus2
and Pluto's much too distant.
(Our folks refused to take us
even though we were insistent3.)
It wasn't up in outer space
our parents gave us birth.
They had us right here safe at home
on dear old planet Earth.
So what I simply can't explain
is why my sister, Janet,
behaves as if she were a creature
from another planet!