# planet ratings, M class. **URL:** \ **Category:** Factual Questions\ **Created:** [January 2, 2003, 10:39am UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183 "2003-01-02T10:39:35Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![the\_duke\_69](https://avatars.discourse-cdn.com/v4/letter/t/48db29/32.png) [@the\_duke\_69](https://boards.straightdope.com/u/the_duke_69)\ **Post date:** [January 2, 2003, 10:39am UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/1 "2003-01-02T10:39:35Z")
Is there a planetary rating such as in “Startrek” and the M class planet rating? ---
**Author:** ![Trader\_of\_shorts](https://avatars.discourse-cdn.com/v4/letter/t/90ced4/32.png) [@Trader\_of\_shorts](https://boards.straightdope.com/u/Trader_of_shorts)\ **Post date:** [January 2, 2003, 10:48am UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/2 "2003-01-02T10:48:11Z")
Hmm do not know … but … Search under google for “M Class planet” you get 2,500 results Searching in google for " M class planet " nasa -trek You get 16 I would say it is ficticious for the moment, but see no reason why they would not use it when the time arives - usually they just say " Earthlike" or “Mars like” or “saturn like” Maybe an astro geek can provide further info. ---
**Author:** ![Zagadka](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zagadka/32/7272_2.png) [@Zagadka](https://boards.straightdope.com/u/Zagadka)\ **Post date:** [January 2, 2003, 10:50am UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/3 "2003-01-02T10:50:02Z")
I don’t think we have seen enough planets to develop a classification system based on that many variables. NASA tends to list planets with data like this: > [@](#): > > Planet: Epsilon Eridani b > Type: Gas Giant > Mass: 0.86 (Jupiter = 1) > Orbital Radius: 3.3 AU > Orbital Period: 2502.1 days > Eccentricity: 0.608 [http://planetquest1.jpl.nasa.gov/atlas/atlas\_search.cfm](http://planetquest1.jpl.nasa.gov/atlas/atlas_search.cfm) ---
**Author:** ![Zagadka](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zagadka/32/7272_2.png) [@Zagadka](https://boards.straightdope.com/u/Zagadka)\ **Post date:** [January 2, 2003, 10:52am UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/4 "2003-01-02T10:52:12Z")
In short, how you can compress a set of conditions based on at least 5 variables to a comprehensible data set is beyond me, but as Trader pointed out, comparing the planet to familiar planets would probably be most efficient. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [January 2, 2003, 11:12am UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/5 "2003-01-02T11:12:52Z")
I have never heard the term M-class outside _Star Trek_, and I’ve sat through a few lectures on planetary astronomy. As I recall in _Star Trek Memories_ by William Shatner, the idea of an M-class planet was invented by Gene Roddenberry as one of the ways of making _Star Trek_ cheap enough to produce. If the crew only visited worlds where they didn’t need spacesuits, they wouldn’t need expensive costumes. Another cost-cutting invention was the transporter, which saved on expensive landing sequences. **Zagadka** , compressing sets of conditions is not at all uncommon in astronomy. You may realize, for instance, that main sequence stars are divided into seven (or so) spectral types: O, B, A, F, G, K, and M. ---
**Author:** ![Berkut](https://avatars.discourse-cdn.com/v4/letter/b/a88e57/32.png) [@Berkut](https://boards.straightdope.com/u/Berkut)\ **Post date:** [January 2, 2003, 11:54am UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/6 "2003-01-02T11:54:45Z")
M Class = **M** ostly harmless ---
**Author:** ![Yossarian](https://avatars.discourse-cdn.com/v4/letter/y/9de0a6/32.png) [@Yossarian](https://boards.straightdope.com/u/Yossarian)\ **Post date:** [January 2, 2003, 3:37pm UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/7 "2003-01-02T15:37:23Z")
The Planetary and Earth sciences being very closely allied, I’d suspect that future classification schemes for other solar systems will be at least initially based on ours as a “type” solar system. Something like “M Class” is far less intuitive than “Earth-like” or “Earth Class”. ---
**Author:** ![Mojo\_the\_Monkey](https://avatars.discourse-cdn.com/v4/letter/m/eada6e/32.png) [@Mojo\_the\_Monkey](https://boards.straightdope.com/u/Mojo_the_Monkey)\ **Post date:** [January 2, 2003, 6:28pm UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/8 "2003-01-02T18:28:21Z")
It was recently established in an episode of _Enterprise_ that the “M” in M-class is an abbreviation of the Vulcan word “Minshara”. Whatever the heck that means. So, it seems obvious that whatever planetary classification system that is used in the Star Trek universe is one that was borrowed from the Vulcans. ---
**Author:** ![Ego\_Mk2](https://avatars.discourse-cdn.com/v4/letter/e/58956e/32.png) [@Ego\_Mk2](https://boards.straightdope.com/u/Ego_Mk2)\ **Post date:** [January 2, 2003, 8:08pm UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/9 "2003-01-02T20:08:14Z")
> [@](#): > > \*Originally posted by Achernar \* > \*\*\*\*You may realize, for instance, that main sequence stars are divided into seven (or so) spectral types: O, B, A, F, G, K, and M. \*\* And N now, from what I’ve heard. Oh, be a fine girl: kiss me now! O big and fat gorilla kill my nanny! 😃 ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [January 3, 2003, 8:55am UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/10 "2003-01-03T08:55:36Z")
Originally there were three types of stars beyond M-type. They were R, N, and S. These fell out of favor, or were absorbed into M-type, or something. I hadn’t heard of N-type regaining any usage, but I have heard of L and T being tacked on to the end. OBAFGKMLT. I really get the impression that beyond the classic seven, you’re well-advised to explain what you mean when you use a letter to describe your star. Also, I should have mentioned that Earth-sized, rocky worlds which are about the right distance from their sun to give them a roughly Earth-like temperature are typically called “Earth-like planets” or “Earths”. This term is usually used in sentences like: “How the heck are we going to locate any Earth-like planets?” We don’t know enough about the atmospheres of extra-solar planets to begin classifying these planets by their atmospheric composition. As I understand it, _Star Trek_’s M-class has, as one of its requirements, that the world have a breathable atmosphere. ---
**Author:** ![Ephemera](https://avatars.discourse-cdn.com/v4/letter/e/8baadc/32.png) [@Ephemera](https://boards.straightdope.com/u/Ephemera)\ **Post date:** [January 3, 2003, 9:02am UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/11 "2003-01-03T09:02:38Z")
An M Class planet in Star Trek is conducive to human life without any sort of technology. If you need domes to breathe or filters to drink the water, it isn’t Class M. ---
**Author:** ![muttrox](https://avatars.discourse-cdn.com/v4/letter/m/a8b319/32.png) [@muttrox](https://boards.straightdope.com/u/muttrox)\ **Post date:** [January 3, 2003, 2:29pm UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/12 "2003-01-03T14:29:28Z")
> [@](#): > > \*Originally posted by Zagadka \* > \*\*In short, how you can compress a set of conditions based on at least 5 variables to a comprehensible data set is beyond me, \*\* Basic statistics, if some of them are correlated, then you get “clusters” of data. As an example, if the orbital radius and orbital period are highly correlated, then you really only need one. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [January 3, 2003, 2:49pm UTC](https://boards.straightdope.com/t/planet-ratings-m-class/146183/13 "2003-01-03T14:49:45Z")
> [@](#): > > \*Originally posted by Zagadka \* > **In short, how you can compress a set of conditions based on at least 5 variables to a comprehensible data set is beyond me** It’s not “compressed” to 5 variables. That’s _all_ we know about those planets. Extrasolar planets are found by measuring the gravitational influense on the host star. The star wobbles back and forth as the planet goes around it, and by measuring the wobble we can calculate the period, radius and eccentricity of the orbit as well as the mass of the planet. The “Gas Giant” designation is speculation, based on the fact that it has similar (or larger) mass to the gas giants in our solar system. Direct observation is possible for some of the larger gas giants, but there are very few observations like that. Imaging smaller (“terrestrial”) planets is impossible with current technology. For that we’ll probably have to wait for the [Terrestrial Planet Finder](http://planetquest.jpl.nasa.gov/TPF/tpf_index.html) space telescope.