Goldilocks zone: Everything you need to know about the habitable sweet spot

适居区：你需要知道的关于适宜居住的甜蜜点的一切

The habitable zone is the region around a star where an orbiting planet could host liquid water and, therefore, possibly support life.

适居带是恒星周围的区域，在该区域内，轨道行星可以容纳液态水，因此可能支持生命。

The habitable zone is also known as the "Goldilocks zone" because planets orbiting at that "just right" distance from a star are not too hot or too cold to host liquid water. If planets are closer to their star, the water turns to steam; if they're farther, it freezes.

宜居带也被称为“金发地带”，因为在距离恒星“恰到好处”的距离上运行的行星不会太热或太冷，无法容纳液态水。如果行星离恒星更近，水就会变成蒸汽；如果他们走得更远，就会结冰。

Some researchers think the potential for liquid water has too simplified a picture of what it takes to support life. Venus, for example, is technically in the sun's habitable zone; its orbit keeps the planet within the area where liquid water could possibly exist. But in reality, the planet's carbon dioxide-rich atmosphere gives it the hottest surface temperatures of any planet in the solar system, and it's unlikely that life exists on its scorching surface or in its skies.

一些研究人员认为，液态水的潜力过于简化了维持生命所需的条件。例如，从技术上讲，金星位于太阳的宜居区；它的轨道将行星保持在可能存在液态水的区域内。但事实上，这颗行星富含二氧化碳的大气层使其表面温度达到了太阳系中任何行星的最高温度，在其灼热的表面或天空中不太可能存在生命。

Related: The 10 most Earth-like exoplanets

相关：10颗最像地球的系外行星

The Goldilocks zone is different around each star. Bigger, hotter stars like the sun, a G-type star, have a wider habitable zone, while smaller red dwarfs confine habitable planets to a narrower range, according to NASA (opens in new tab). But G-type stars are shorter-lived (on a galaxy timescale, that is) than some other types of stars. One abundant kind of star, K-type stars, can burn for tens of billions of years and, because of their stability, might have the most promising habitable zones.

每颗恒星周围的金发女郎区域都不同。NASA表示，像太阳这样更大、更热的G型恒星有更宽的适居区，而较小的红矮星则将适居行星限制在更窄的范围内。但G型恒星比其他类型的恒星寿命更短（在银河系时间尺度上）。一种丰富的恒星，K型恒星，可以燃烧数百亿年，由于它们的稳定性，可能拥有最有希望的宜居区。

But stars are individuals, too; for example, some red dwarfs are unpredictable, sending sterilizing flares toward their planets, while others are steady and reliably calm. So while two stars may have similar habitable zones and similarly sized planets, one star system might contain a much more promising candidate for life.

但明星也是个人；例如，一些红矮星是不可预测的，向它们的行星发出杀菌的耀斑，而另一些则是稳定而可靠的平静。因此，虽然两颗恒星可能有相似的适居带和大小相似的行星，但一颗恒星系统可能包含一个更有希望的生命候选者。

One example is the exoplanet TOI 700 d, discovered in 2020 by NASA's Transiting Exoplanet Survey Satellite (TESS). The star that TOI 700 d orbits could have been considered an unlikely home for life-bearing planets based on its type and its habitable zone alone. However, it’s a particularly “quiet star,” according to its discoverers, and has been stable long enough that on one of its planets, life could indeed have taken hold.

一个例子是2020年由NASA的凌日外行星探测卫星（TESS）发现的系外行星TOI 700 d。TOI 700 d轨道上的这颗恒星，单从其类型和适居带来看，可能被认为是不太可能存在生命行星的家园。然而，根据它的发现者的说法，它是一颗特别“安静的恒星”，并且已经稳定了足够长的时间，以至于在它的一颗行星上，生命确实可能已经存在。

A star's habitable zone does not depend on the types of planets that are actually in the region. Gas giants are less likely to harbor life, according to NASA. So, in addition to searching for planets in stars' habitable zones, researchers look for worlds that resemble Earth in size, atmosphere or chemical composition.

恒星的适居带并不取决于该区域内实际存在的行星类型。据美国国家航空航天局（NASA）称，天然气巨头不太可能拥有生命。因此，除了在恒星的宜居区寻找行星外，研究人员还寻找在大小、大气或化学成分上与地球相似的行星。

Related: Superhabitable planets: Alien worlds that may be more habitable than Earth

相关：超级可居住行星：可能比地球更适合居住的外星世界

Venus, Earth and Mars all orbit within the sun's habitable zone.

金星、地球和火星都在太阳的可居住区内运行。

Venus is just far enough away from the sun for the planet to have the possibility of hosting liquid water, according to NASA (opens in new tab). However, Venus' runaway greenhouse atmosphere makes the planet even hotter than Mercury, which is much closer to the sun. That atmosphere eliminates the possibility of life (as we would recognize it) on the planet's surface.

据美国国家航空航天局（NASA）称，金星距离太阳的距离刚好足够，这颗行星有可能容纳液态水（在新标签中打开）。然而，金星失控的温室气体使这颗行星比离太阳更近的水星还要热。这种大气层消除了地球表面存在生命的可能性（正如我们所认识到的那样）。

Earth is squarely in the middle of the sun's habitable zone. Some researchers say that isn't a coincidence; after all, we created the idea of "habitable zones" to look for planets like ours. To be fair, we have only one frame of reference. But as a result, we may be overlooking even better conditions for life than those on Earth because our view is too narrow.

地球正好位于太阳可居住区的中间。一些研究人员表示，这并非巧合；毕竟，我们创造了“宜居区”的概念，以寻找像我们这样的行星。公平地说，我们只有一个参照系。但结果，我们可能会忽视比地球上更好的生活条件，因为我们的视野太狭隘。

Mars is at the far, chilly edge of the sun's habitable zone. But there is evidence that an ocean may have once flowed on Mars, and NASA's Perseverance rover is still busily sampling for microbial life that could be hidden below the planet's surface.

火星位于太阳宜居带的遥远、寒冷的边缘。但有证据表明，火星上可能曾经流过海洋，美国宇航局的“毅力号”火星车仍在忙碌地采样，寻找可能隐藏在火星表面以下的微生物生命。

Researchers use the idea of a habitable zone to narrow down which exoplanets might be good candidates in the search for extraterrestrial life.

研究人员利用可居住区的概念来缩小哪些系外行星可能是寻找外星生命的良好候选行星。

As of early 2023, NASA's Kepler Space Telescope and TESS missions have detected and cataloged more than 5,000 exoplanets, according to the NASA Exoplanet Archive (opens in new tab), and those represent just a tiny fraction of the planets we're likely to discover as we keep looking. Kepler showed that, on average, every star has at least one planet.

根据NASA外行星档案（在新标签中打开），截至2023年初，NASA的开普勒太空望远镜和TESS任务已经探测并编目了5000多颗系外行星，而这些只是我们继续寻找可能发现的行星的一小部分。开普勒表明，平均而言，每颗恒星至少有一颗行星。

If you're excited about the possibility of civilizations in space, check out what's new at the SETI Institute (opens in new tab), an organization dedicated to the search for extraterrestrial intelligence. Try your hand at a little exoplanet exploration of your own with NASA’s citizen science project (opens in new tab). And if you want to dive deeper into the search for habitable worlds, read "The Smallest Lights in the Universe (opens in new tab)" (Crown, 2020), an astrophysicist's memoir about searching the universe while appreciating life on Earth.

如果你对太空文明的可能性感到兴奋，请查看SETI研究所（在新标签中打开）的最新动态，该机构致力于寻找外星智慧。在NASA的公民科学项目（在新标签中打开）中，尝试一下自己的系外行星探索。如果你想深入探索适合居住的世界，请阅读《宇宙中最小的光（在新标签中打开）》（Crown，2020），这是一本天体物理学家的回忆录，讲述了在欣赏地球生命的同时探索宇宙。

De La Torre, L. B. (2022, December 15). What is the habitable zone? Exoplanet Exploration: Planets Beyond Our Solar System. NASA/JPL. https://exoplanets.nasa.gov/resources/2255/what-is-the-habitable-zone (opens in new tab)

德拉托雷，L.B.（2022年12月15日）。什么是宜居区？外行星探索：太阳系以外的行星。美国国家航空航天局/JPL。https://exoplanets.nasa.gov/resources/2255/what-is-the-habitable-zone（在新选项卡中打开）

NASA Exoplanet Science Institute. Exoplanet and candidate statistics. (n.d.). NASA Exoplanet Archive. Retrieved January 27, 2023, from https://exoplanetarchive.ipac.caltech.edu/docs/counts_detail.html (opens in new tab)

美国宇航局系外行星科学研究所。系外行星和候选统计。（未注明）。美国宇航局系外行星档案馆。检索于2023年1月27日，来自https://exoplanetarchive.ipac.caltech.edu/docs/counts_detail.html（在新选项卡中打开）

NASA. (2021, April 2). The search for life. Exoplanet Exploration: Planets Beyond Our Solar System. https://exoplanets.nasa.gov/search-for-life/habitable-zone (opens in new tab)

美国宇航局。（二零二一年四月二日）。寻找生命。太阳系以外的行星。https://exoplanets.nasa.gov/search-for-life/habitable-zone（在新选项卡中打开）