Classing planets

[Gnom]

Something that has always eluded me...
Why Class-M? What does the M stand for?  

[Holodoc]

M is the middle letter of the alphabet more or less. Maybe they rate and place them on either end, spaced in distance to M according to certain elemental factors (like one direction may have more of one thing and the other direction more another and less of that)? Then the farthest on the alphabet means the more difficult to live exist without environmental assistance if at all.

Just a guess here.

[Andorian_Incident]

I don't know why they decided to call it M-class in the first place, but we've learned from Enterprise that it comes from the Vulcans' Minshara-Class planets.

Two possible explanations for that were brought up in the Enterprise forum a couple months ago.  One is that Minshara is the Vulcan word for "life-supporting" or some equivalent, and the other is that it's the first planet that the Vulcans came across that had life on it.  Or possibly both hypothesis are right.

I think the book "Worlds of the Federation" had a list of what the different class planets were and their characteristics, but of course that book is not canon, and most of the book is now outdated.

[Dj]

Class J planets usually are, hot planets, usually not having a breathable atmosphere.

[StolenThunder]

Ok, just a quick run through...

Class D planets are small rocky planetoids. Regula was a class D world.

Class H planets are generally extremely dry, although sometimes habitable. Tau Cygna V.

Class J planets are gas giants with turbulent atmospheres, in which wind speeds of over 10,000km/h are not unknown. Jupiter and Saturn.

Class K planets are unsuitable for humanoid life, even though their gravity fields can fall within M class norms. Class K planets, such as the planet Mudd, are adaptable for human life only with the use of pressure domes, and life support systems.

Class L planets are generally small, rocky, terrestrial worlds with oxygen-argon atmospheres. These worlds can sometimes support life, although this is often limited to plant forms. Planet Indri VIII was Class L.

Class M planets are small, rocky, terrestrial worlds with oxygen-nitrogen atmospheres, and are highly supportive of organic life. Earth, Vulcan, and many others are M Class planets.

[From the Star Trek encyclopaedia.]

[Dj]

Hm....argh... I could have sworn that the planet in Demon(which I just spent 30 minutes trying to figure out the name of that episode) was a J class planet, but it's Y.

Well, Y class planets have a toxic atmosphere and at least sometimes contain high concentrations of deuterium.