The Habitable Zone
宇宙生命奥秘
适居带(HZ)是天文学上给一种空间的名称，指的是那里的情况有利于生物的存在，或许可以发现像地球这样的生命体。有两种区域是有可能的，一个是在行星系内，另一个则存在于星系之中。在适合的区域内的行星和天然卫星是最佳的候选者，这些地球外的生命有能力生活在类似我们的环境下。天文学家相信生命最可能发生在像太阳系这样的星周盘适居带(CHZ)和大星系的星系适居带 (GHZ)内。适居带也许是指"生命带"、"绿带"或"Goldilocks带"(因为既不太热也不太冷，就是刚好)。在我们的太阳系，适居带被认为从0.95天文单位延伸至1.37天文单位。
Y: Do you think there's life on other planets Don?
D: It seems perfectly reasonable that there would be Ya?l. what with how unfathomably large the universe is.Don't you think？
Y:I do.But then again, life is a tricky thing. So much has to fall into place for the conditions for life as we know it to be possible.For instance, a planet has to be just the right distance from the star it revolves around.
D:How is that?
Y:If it’s too close to its star, the heat from the star would cause any water on the planet to boil away. If it’s too far away, the opposite problem occurs: the cold temperature would cause water to freeze. The range of distance from a star that will allow water to remain a liquid is called the habitable zone.
D:So we Earthlings are lucky I guess that we are just the right distance away from the sun.
Y:Very lucky it seems.In 2007, scientists discovered the first two Earth-like planets outside our solar system that appear to be located near or within their star’s habitable zone. Previously discovered planets have had masses more akin to Jupiter’s. The planets orbit the same star and are known as Gliese 581c and Gliese 581d.
D:Wow,so there is other life out there?
Y:Not so fast, upon further investigation, it seems that Gliese 581d may be the only one of the two actually in the habitable zone, and its orbit seems to take it in and out of the zone. Not to mention as I said, a lot of factors must come into play for life to exist. Being within the habitable zone is just one of them.
译文
Y:Don，你认为其他行星上会有生命存在吗？
D:似乎完全有理由相信有生命存在。宇宙如此之大，深不可测，不是吗？
Y:的确如此。但是话又说回来，生命的存在是一件极其有难度的事。据我们所知，生命存在的可能性需要满足众多适合生存的条件。比如说，行星与其所围绕旋转的恒星之间的距离是否适当。
D:这有什么关系？
Y:如果太近，来自恒星的热量会导致行星上水分蒸发，与之相反，要是距离太远，温度太低会致使水冻结。与恒星之间的距离要能保持水呈现的是液体状态，这个范围被称作适居带。
D:那我们地球岂不是很幸运，与太阳之间的距离正当适宜。
Y:是非常的幸运。2007年，科学家们在太阳系以外首次发现两颗类似地球，可能位于适居带附近的行星，而之前发现的行星更类似于木星。这两颗行星都围绕格利泽581恒星转动，因此他们被称作格利泽581d和格利泽581c。
D:哇！那探索到有生命存在吗？
Y:没那么快。据进一步调查研究发现，格利泽581d可能是二者中在适居区以内的行星，而且其运行轨道使其在适居区内游离。更何况正如我所说的，生命存在还有诸多因素要考虑，在适居区只是其中之一。 |