* *环绕恒星的宜居带* *有(一个)(http://www.universetoday.com/32622/habitable-zone/)[一些](http://www.britannica.com/EBchecked/topic/1674268/habitable-zone)(页)(https://en.wikipedia.org/wiki/Circumstellar_habitable_zone),详细解释这个概念,但主旨是环绕恒星的宜居带(我定义)>的恒星周围的区域内类似地球的行星表面有液态水。然而,更详细的观察(木卫二)(https://en.wikipedia.org/wiki/Europa_(月球)),其可能的地下海洋,和(泰坦)(https://en.wikipedia.org/wiki/Titan_(月球)),以其烃湖泊,定义可能被修改:>,体内的恒星周围的区域可以有液态水,或其他化合物适合生命的形成会产生;另外,周边地区一个巨型气体行星,卫星可以被潮汐力,这样激烈的化合物可以存在。后者的部分,当然只适用于卫星。银河系中的“宜居地带”(见[这](http://astro.unl.edu/naap/habitablezones/ghz.html)和[这](https://en.wikipedia.org/wiki/Galactic_habitable_zone))是另一个-稍微没有那么明确的可居住星球应该躺的地方。你可以计算适居带恒星周围的基于定义:恒星的光度,为主。有poorly-explained公式[这](http://www.astro.sunysb.edu/fwalter/AST101/habzone.html),尽管(行星生物学)(http://www.planetarybiology.com/calculating_habitable_zone.html)提供了一个更明确的推导。两个重要的方程是:$ $ r_i = \√6{\压裂{L_{\文本{明星}}}{1.1}}$ $ $ $ r_o = \√6{\压裂{L_{\文本{明星}}}{0.53}},r_i美元和美元r_o内外半径,美元和美元L_{\文本{明星}}$是恒星的光度。但是,请注意,这些都是传统定义的宜居区,忽视非H_2O的化合物和美元潮汐加热卫星轨道的气态巨行星。[这](http://xxx.lanl.gov/pdf/1301.6674v2.pdf)预印,Kopparapu et al .,确实给了另一个有趣的公式:$ $ d = \离开(\压裂{L / L_ {\ odot}} {S_ {eff}} \右)^{0.5}\文本{盟}$ $ $ S_ {eff} $是一个参数决定的有效温度T_ {eff}识别美元一颗行星的距离和一些系数,以及太阳的S_ {eff}美元。 But those findings are rather new, so I'd stick with the older formulas. So the habitable zone is determined primarily by the star's luminosity. **Mass** An atmosphere is generally considered a must for planets with Earth-like lifeforms. Low-mass bodies, such as the Moon, can't hold on to one, and that's one of the reasons that moons have not been of as much interest as planets have been. Atmospheres, among other things, can keep the planet at a nice temperature and allow distinct climates to form. As [this site](http://triplehelixblog.com/2012/06/criteria-for-habitable-planets-and-implications-for-earth/) elaborates on, they also help protect the planet from radiation like UV rays. Our ozone layer is really helpful in that regard. Mass isn't the only thing that helps a body keep its atmosphere. For example, Titan is relatively low-mass (although relatively high-mass for moons), yet it still has [an atmosphere](https://en.wikipedia.org/wiki/Atmosphere_of_Titan). This is because the solar wind - which can hurt atmospheres - is so weak at Titan's distance from the Sun. To expand on what gansub mentioned: Magnetic fields are important because they are extremely useful when it comes to helping a planet retain its atmosphere. As Luhmann and Russell explain in ["Mars: Magnetic Field and Magnetosphere"](http://www-ssc.igpp.ucla.edu/personnel/russell/papers/mars_mag/), Mars lost its magnetic field long ago, and so the solar wind is gradually stripping it away, albeit at a really slow rate. **Rotation** This section is based a lot on [this paper](http://arxiv.org/pdf/1404.4992v1.pdf), by Yang et al. It, too is recent, so keep that in mind. Before I get into the paper, I'll say this: Rotation helps because it keeps one side of the planet from being baked while the other side freezes. [Tidally-locked planets](https://en.wikipedia.org/wiki/Tidal_locking) aren't the greatest places for life. A decently-fast rotation can really help. Anyway, Yang et al. came to this conclusion (as voiced in their opening sentence): > Planetary rotation rate is a key parameter in determining atmospheric circulation and hence the spatial pattern of clouds. Since clouds can exert a dominant control on planetary radiation balance, rotation rate could be critical for determining mean planetary climate. In other words, rotation helps clouds, and since clouds help govern the climate of the planet, a proper rotation rate can make the climate less extreme.