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Some
Super Earths More Like Mini Neptunes
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Some "super-Earths" will never evolve to resemble our
planet, a new study suggests. Researchers looked at seven of these
worlds—distant planets whose mass lies between one and 10 times
ours—including 55
Cancri e(at right, compared to Earth) and GJ1214b, evaluating how the x-ray and extreme ultraviolet
radiation emitted by their parent stars might affect their
atmospheres over their remaining lifetimes. Even though many of the
planets orbit their stars very closely and have high temperatures,
which in turn causes their hydrogen-rich atmospheres to expand and
a fraction of the gases to escape the planet over time,
it's unlikely
that the planets will lose enough of their atmosphere to become
rocky bodies like Earth, the researchers report online today in theMonthly Notices of the Royal Astronomical
Society. And if any planets similar to these orbit in their
parents stars' habitable zone, substantially farther from the home
star where liquid water might more likely exist, their atmospheres
will lose even smaller amounts of hydrogen-bearing compounds over
time, the researchers note. So, instead of thinking of these
planets as super-Earths, astronomers should probably think of them
as "mini-Neptunes"—a planet in our solar system that weighs about
17 times the mass of Earth and is swaddled in hydrogen-rich gases.
Even if these mini-Neptunes never become habitable, however, many
scientists have previously proposed that any smaller, rockier
Earth-sized moons orbiting the gas giants could nevertheless host
life as we know it. |
一项新研究显示，一些超级地球将永远不会演化成为类似于我们地球的行星。研究人员观察了七个这样的星球，这些远方的行星质量在地球的1倍与10倍之间，包括55巨蟹e（图为该星球与地球的比较）和GJ1214b，评估了在它们的余生之中主恒星所释放的Ｘ射线和极端紫外线对大气的影响。今天，研究人员在《皇家天文学会月刊》在线版上报道说：许多这样的行星在很近的距离上围绕恒星旋转，而且拥有很高的温度，而高温又引起富氢大气膨胀，随着时间的推移一小部分气体就会逃离行星；尽管如此，这些行星不大可能失去足够多的气体而变成像我们地球这样的岩石星球。研究人员指出：如果有类似的行星在主恒星系统的可居住带上做环绕运动，这样就会距离主恒星远得多，更有可能存在液态水，但是它们的大气随着时间的推移将会损失更少的含氢化合物。因此，天文学家们不应把这些行星当作超级地球，而或许应该把它们当作“微型海王星”。海王星是太阳系中的一颗行星，质量为地球的17倍，被富氢气体包裹着。然而，尽管这些微型海王星永远不会变得可以居住，但是许多科学家们以前提出过：正如我们所了解到的那样，任何环绕这些气态巨星的地球一般大小的较小型多岩石卫星都可能拥有生命。 |
译自：美国《科学》杂志网站（4 February 2013, 2:25
PM）
原著：Sid
Perkins![]()
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青春就应该这样绽放 游戏测试：三国时期谁是你最好的兄弟！！ 你不得不信的星座秘密