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It's pretty reasonable to assume that Earth is the ultimate Eden in the universe, a paradise planet that's just perfect for life.
将地球视为宇宙里最后一个伊甸园是合情合理的，毕竟这是里天堂一般的行星，适合生命存在。
After all, not only is it our home, but it's also the only place we know life has evolved.
地球不仅是我们的家，也是目前所知道的唯一一个能孕育生命的地方。
But, as it turns out, there might be even better places to live, planets even more suitable for life.
但我们发现，可能会有居住环境更好的星球，更适合生命存在的星球。
Scientists call them superhabitable planets.
科学家称之为超级适居行星。
They're worlds that could sustain life more than five times longer than Earth,
这样的行星宜居程度是地球的5倍多。
and while we haven't found one for sure yet, there might be billions of them lurking in our galaxy alone.
虽然目前我们连一个都没找到，但其实我们所在的星系里可能就潜伏着数百万颗这样的行星。
The idea of superhabitable planets was introduced in 2014 by two North American researchers: René Heller and John Armstrong.
超级适居行星的概念是2014年2位北美洲研究人员提出的，他们是莱茵·希勒和小约翰·阿姆斯特朗。
And while each planet could look a little different, they would have two main features that would make them better than Earth.
虽然每颗行星的样子都有些许的不同，但他们有2个主要特征是优于地球的。
First, these planets would be able to maintain liquid water much longer than ours.
首先，这些行星保留液态水的时间比地球长。
Earth's cozy, life-sustaining environment is largely thanks to its position relative to the Sun, along with other factors like the atmosphere.
地球的环境之所以舒适宜居是因为其跟太阳之间的位置关系比较适中，除此之外还有一些因素，如大气层。
We exist in what's called the habitable zone, or the area around a star where liquid water can exist on a planet's surface.
人类生活在所谓的宜居地带，该地带是恒星附近的区域。在这里，液态水可以在某颗行星的表面存在。
But that won't last forever. In five billion years or so, toward the end of its lifetime, our Sun will have expanded into a larger red giant.
但液态水的存在不是永久不变的。大约50亿年后，地球的生命周期就会终结，太阳就会扩张到更大的红色星体中。
And it will actually go through some pretty major changes even before that point.
在那一天到来之前，太阳还会经历一些其他的重大变化。
Over time, as the Sun burns through the fuel in its core, it will gradually become hotter and brighter.
随着时间的流逝，太阳内核的燃料会渐渐燃烧殆尽，温度和亮度都会越来越高。
That means it will let out more energy, so the habitable zone will migrate outward.
也就是说，太阳会释放出更多的能量，这样的话，宜居地带就会向外移动。
For us, that means that it will eventually become so hot that the water on Earth will be vaporized.
对我们来说，这意味着太阳最终会达到极高的温度，致使地球上的水蒸发。
Which isn't exactly great for anything that wants to live here.
这会使地球的环境不再宜居。
The Sun's habitable zone is currently pushing outwards at about a meter a year.
每一年，太阳周围的宜居地带都会向外扩张一米左右。
And it's predicted that we'll fall off the zone's inner edge in some 1.75 billion years.
据预测，大概17.5亿年后，地球就会脱离宜居地带的内缘。
Two billion years is a really long time, but it turns out that other planets will stay in their stars' habitable zones for much longer, because they'll orbit stars better than our Sun.
20亿年的时间虽然很长，但我们发现，其他行星在宜居地带中待的时间比我们还要长，因为他们所环绕的恒星比地球的生命周期更长。
The Sun is a G-class yellow star, or one of the mid-sized, longer-lived stars in the universe.
太阳是G型黄星，即宇宙里大小适中、寿命较长的恒星。
But smaller stars actually live even longer.
但越小的恒星，生命周期就越长。
That's because there's less gravity to power the fusion reactions in the core, so they burn slower, and their fuel lasts longer.
这是因为，他们受到的引力作用更小，内核发生的聚变反应也就更少，所以燃烧速度更慢，燃料可以持续的时间更久。
That means their habitable zones will migrate outwards more slowly, too.
也就是说，更小的恒星，其宜居地带向外扩张的速度就更慢。
So a planet will be able to maintain the right temperatures for liquid water for many more years.
所以，围绕他们的行星保留液态水适宜温度的时间就更长。
The smallest stars are M-class red dwarfs, which live for trillions of years.
宇宙中最小的恒星是M型的红矮星，可以存续数万亿年的时间。
But they come with their own problems, like explosive solar flares.
但这类恒星也有自己的苦恼，比如爆炸性的太阳耀斑。
So instead, scientists think the ideal stars for habitable planets are the intermediate K-class orange stars.
所以，科学家反而觉得宜居行星的理想恒星是处于中间段的K型橙星。
They're about 50 to 80% the mass of our Sun and can live more than 30 or 40 billion years.
这类恒星的质量是太阳的约50%-80%，可以存续300多亿-400亿年的时间。
But superhabitability doesn't just come down to the star.
超级适居的希望并不只在恒星身上。
The second trick to being better than Earth involves tweaking the planet itself; its atmosphere, geology, and geography.
想要实现比地球更好的宜居环境，还可以从行星自身上抓，即行星的大气层、地质和地形。
Earth is pretty good, but we still have deserts, ice caps, and big chunks of deep ocean without as much complex life.
地球已经相当不错了，但地球上依然有沙漠、冰冠、复杂生命无法生存的大片深海区域。
A superhabitable planet would do away with these barren landscapes to support more species and more diversity.
超级适居的行星上是不会存在这类不适宜生命生存的地貌的，反而可以支持更多的物种存在，支持生物多样性。
And one of the ways of doing that is to be more massive than Earth.
其中一种实现生物多样性的方式就是比地球质量更大。
According to researchers, an Earth-like planet maybe twice as massive as ours would have a bunch of great things for life.
研究人员认为，与地球相似的行星，其质量可能是地球的2倍，这样才能适宜生命存在。
For one, it would have more gravity, which would help to hold on to more atmospheric gases.
一方面原因是：这样的行星引力更大，能留住更多的大气层气体。
That would give the planet more greenhouse-style warming, so it could orbit a little farther from its star and still stay warm enough to have liquid water.
这样，行星就会出现更多与温室效应类似的变暖情况，这样他们离其所环绕恒星的距离就会更远，但温度又可以足够温暖，能够让液态水存续更久。
That would buy it even more time before it fell off the inner edge of the habitable zone.
这样其脱离宜居地带内缘的时间就会更久。
Stronger gravity would probably also help heat the center of the planet, which might cause more active plate tectonics.
引力越大，行星地心的温度就越高，这样可能会导致板块活动更频繁。
That would likely be a good thing for life.
这对于生命的存续来说是一件好事。
A geologically active planet would keep renewing elements like phosphorus and calcium, which life needs to thrive.
板块活跃的行星，磷元素和钙元素就会保持更久的活性，这样生命才能保持活跃。
All the shifting plates would keep bringing the elements to the surface, stopping them from getting trapped in the planet's crust for too long.
板块的不断活动会将元素带到地表，这样，元素就不会在地壳中积压过久的时间。
And, if that wasn't enough, higher gravity would also cause the iron core of a planet like this to be hotter.
除此之外，由于引力更大了，这类行星含铁的地心温度就会更高。
That would likely result in a stronger magnetic field, which would protect the planet's atmosphere from particles and flares flying off its star.
这样会使磁场更强，保护其大气层不受粒子和耀斑的撞击。
So, in around two billion years, when it's time for humans to find a new home, we have our checklist of requirements.
所以，大概20亿年后，人类就要寻找新的家园了。找新家园是有几点要求的。
And the good news is, there might be a pretty good chance of us finding one of these superhabitable worlds.
不过，好消息是：我们还是很有可能找到超级适居行星的。
When scientists peer into the night sky, K-class stars are actually about twice as common as Sun-like stars.
科学家观测夜空发现，K型恒星的数量是与地球类似的恒星数量的近2倍。
And since research suggests there are planets around most of the stars in the universe, there's potential for more than 10 billion superhabitable planets in the Milky Way alone.
而且鉴于有研究表明宇宙里大多数恒星周围都有行星，所以单是银河系里可能就有100多亿颗超级适居行星。
Using new space telescopes like TESS, scientists soon hope to study the characteristics and atmospheres of promising candidates, like one 1200 light-years away called Kepler-62f.
通过使用凌星系外行星巡天望远镜，科学家不久后就有希望研究候选行星的特征和大气层，比如有一颗备选行星叫开普勒-62f，距离我们1200光年远。
Then, they can see if their hypotheses about superhabitability hold up.
那时候，科学家就可以检测他们关于超级适居行星的假设是否成立了。
So, while it might come as a bit of an unwelcome surprise that Earth probably isn't the best place in the universe, there's no need to be too bummed out.
地球很有可能不是宇宙里最宜居星体的这件事虽然让我们震惊又颇感失望，但也不必太过丧气。
We're well on our way to finding a new Eden out there among the stars.
我们已经开始着手在茫茫恒星中寻找新的伊甸园了。
Then all we have to do is figure out how to get there.
之后，我们就只需要搞明白如何抵达新的伊甸园就可以了。
Thanks for watching this episode of SciShow Space!
感谢收看本期的《太空科学秀》！
Whether we're talking about planets, galaxies, or missions, we love learning about the universe and exploring our place within it.
不管我们讨论的主题是行星、星系和空间任务，我们都钟爱了解宇宙并探索宇宙中的各种地方。
If you'd like to help us keep making videos like this one, you can go to patreon.com/scishow.
如果您想要帮助我们制作类似于本期的视频，可以访问patreon.com/scishow。
And to all of our patrons, thank you! We couldn't do this without you.
在此感谢我们栏目的所有忠实粉丝，没有你们，就没有我们的栏目。
