Water World Is New Type of Planet
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Talk about a sauna. Data gathered by the Hubble Space Telescope suggest that a planet tightly circling a star 40 light-years from Earth is a water world swaddled in a thick, steamy atmosphere. Previous observations of GJ1214b (artist's concept shown), which was first discovered in 2009 and has an estimated surface temperature of about 230°C, couldn't eliminate the possibility that the planet's atmosphere was simply hazy rather than steamy. But the new observations, detailed online in The Astrophysical Journal, reveal that the atmosphere transmits light consistently across a broad range of wavelengths—which tips the balance strongly toward an atmosphere mostly composed of water vapor, the researchers say, because a hazy atmosphere would be more transparent to infrared light than to visible wavelengths. While our solar system contains rocky worlds such as Venus and Earth, gas giants such as Jupiter and Saturn, and icy orbs such as Pluto—and other solar systems sport "lava worlds" and "hot Jupiters"—GJ1214b is the first planet discovered to be composed largely of water rather than rock. Scientists estimate that GJ1214b is about 2.7 times Earth's diameter and weighs about seven times as much, giving the planet a density of about 2 grams per cubic centimeter compared with water's density of 1 gram per cubic centimeter and Earth's average density of 5.5 grams per cubic centimeter. |
讲一讲类似桑拿浴的情况。从哈勃太空望远镜搜集来的资料显示：一颗行星在近围围绕着一颗恒星旋转，该恒星距离地球40光年，该行星是一颗水星球，裹着一层厚厚的充满水汽的大气。行星GJ1214b（见艺术家提供的概念图）最初是2009年被发现的，据估计表面温度大约为230°C。以前的观察没有排除这种可能性：这颗行星上的大气只是雾气而不是水蒸气。但是，《天体物理学杂志》在线版上详细阐述的新一轮观察显示：该行星大气在宽泛的波长范围内都能够一致地传播光线，因而有力地倾向于其大气主要是由水蒸气构成的。研究人员称，原因是大气中的雾气对于红外光比对于可见光更加透明。尽管我们太阳系包含岩石星球像金星和地球，也包含气态巨星像木星和土星，还包含冰封的球体像冥王星，尽管别的恒星系统拥有“熔岩星球”和“热木星”，但是像GJ1214b这样主要由水而不是岩石构成的行星还是第一次发现的。科学家们估计，GJ1214b大约是地球直径的2.7倍，大约是地球质量的7倍，其密度大约为每立方厘米2克。相比之下，水的密度为每立方厘米1克，地球的平均密度为每立方厘米5.5克。 |
译自：美国《科学》杂志网站（21 February 2012, 12:40 PM）
原著：Sid Perkins
