Umm…“Earth” has already been given as an answer. I assume since Anal Scurvy hasn’t acknowledge it, then it’s incorrect. Otherwise, “Earth” would be my first guess, as well.
“Vitamin C deficient bunghole?”
home?
Well, since it’s Anal Scurvy asking this question, I’m going to have to go with the MOON 
Vulcan? Not from Star Trek–the planet hypothesized to be closer to the sun than Mercury. Mercury’s orbit is irregular and couldn’t be accounted for in classical physics, so some scientists thought there might be another planet influencing it’s orbit. But then Einstein and his e=mc[sup]2[/sup] came along. If I’m understanding it correctly (if not, I’m sure The Bad Astronomer or some such character will come along to correct me), the force of the sun’s gravity can be thought of as an additional mass, which accounts for Mercury’s perturbations.
So if you count planets that don’t really exist, I say Vulcan.
Assuming you made a typo in your “secret question”, I’ll guess a fern.
According to this link:
http://my.voyager.net/~stargazer/mercury.html
It’s the most ignored planet in the solar system. Anal Scurvey’s secret question is very open ended, with many possible answers, as I see it. Of course I suck at riddles…
My WAG, on the Greek vs Roman tip, is HERMES.
Maybe it’s “what is the first plan, E.T.”?
answer: phonehome
Or maybe pravnik, along your train of thought, it could be, "What is the first plane-T (plain tea) and of course that would be english breakfast. Nothin’ much plainer than that!
Correcting a misconception - actually we do care, because often a post of that kind is followed by a frantic e-mail asking us to edit the post to remove the confidential information. Do not post passwords / addresses / phone numbers at the message board please.
cloaca
it’s just a cool word, dude.
Underpants.
Ha! I Knew you still had that thing for underpants, SPOOFE!
Nope, nope, nope. You’re still all wrong. Not even close. You don’t need to know anything at all about astronomy.
Abel, got a great chuckle out of that.
Moon actually wouldn’t be a bad guess if it had anything to do with astronomy. The moon and Earth are closer in mass than any other planet/satellite (except Pluto/Charon) and some say we’re actually more of a double planet than a planet/satellite.
But I digress…back to out-of-the-box…
witfp?
Only when the right people are in ‘em, darlin’.
What is the first planet? A planet.
What is the second planet? A planet, what a coinky-dink.
What is the third planet? A planet. I see a pattern.
Mercury? Plain ol’, w/out translation to Latin or Greek or whatever Hermes is (which would have been my other choice)?