最小的系外行星（图） 

虽说根本不象家园，但就系外行星来说，比起天文学家们所遇到的任何其他行星，它在大小上更为接近地球。

The Smallest Extrasolar Planet

When it comes to planets outside our solar system, smaller is better. That's because smaller planets are more likely to resemble Earth. So the discovery of the smallest known extrasolar planet, announced today at the June meeting of the American Astronomical Society in St. Louis, Missouri, comes as good news. "It gives us hope of finding lots of habitable planets," says astronomer Sara Seager of the Massachusetts Institute of Technology in Cambridge, who was not involved in the discovery.	就太阳系以外的行星而言，越小就越理想，因为较小的行星更有可能跟地球类似。因此，今天在密苏里州圣路易斯举行的美国天文学会六月份会议上，科学家们宣布发现了最小的已知系外行星，这是个好消息。“这使我们有望发现许多适合居住的行星，”剑桥麻省理工学院的天文学家萨拉·西格说。西格没有参与这项发现。
The detection comes courtesy of a technique called microlensing. Employed by consortia that operate global networks of telescopes (the Optical Gravitational Lensing Experiment and Microlensing Observations in Astrophysics), microlensing allows continuous monitoring for subtle brightening of far-distant stars as a relatively nearby star passes in front of them. The nearer star's gravity can slightly bend--or lens--the background star's light toward Earth, temporarily brightening it. If a planet circling the nearer star also lines up and bends some starlight, the network picks up a secondary brightening.	该发现借助一种叫做“微引力透镜”的技术。天文协会启动全球的望远镜网络，利用微引力透镜效应，可以连续监视诸多远距离恒星微妙的亮度增加情况。当一颗较近的恒星在遥远的恒星前面经过时，较远恒星的亮度就会有所增加。较近恒星的引力可以使背景恒星射向地球的光线发生折射，暂时地使其更加明亮。如果一颗行星围绕着较近的恒星旋转，若与其恒星及背景恒星排列成直线，也会使恒星的一些光线发生折射，望远镜网络可以探测到亮度的再度增加。
At the meeting, astronomer David Bennett of the University of Notre Dame in Indiana, speaking for the consortia, announced the microlensing discovery of a planet just three times the mass of Earth. Most of the 300 or so known extrasolar planets are many times the mass of Jupiter, or thousands of times the mass of Earth. The newly discovered planet, which the team is referring to as MOA-2007-BLG-192L, orbits its star at 70% of the sun-Earth distance. That means the planet probably formed with lots of ice and gases, Bennett said, more like Neptune in composition than Earth.	在会议上，印第安纳圣母大学的天文学家大卫·贝内特代表天文协会发了言。他宣布说，利用微引力透镜技术发现的这颗行星仅仅是地球质量的三倍。然而，在已知的约300颗系外行星中，多数行星的质量是木星的许多倍。这颗新发现的行星，被研究小组称为MOA-2007-BLG-192L，公转轨道距其恒星的距离为地球到太阳距离的70％。贝内特指出，这意味着该行星很可能是由许多冰和大量气体构成的，在构成成分上更象海王星，而不象地球。
The planet's host star is small as well. At roughly 6% the mass of our sun, the star is probably too small to sustain fusion reactions in its core, said Bennett, making it a dimly glowing brown dwarf.	该行星的主恒星也很小，约为太阳质量的6％。因此贝内特称，这颗恒星太小，其核心部分很可能无法维持聚变反应，使其成为光线暗淡的褐矮星。
Bennett said the microlensing technique holds promise for finding planets even closer in size to Earth. What's more, he noted, future orbiting telescopes may be able to image a planet distinct from its star and therefore search for signs of life.	贝内特说，微引力透镜技术有望用来发现跟地球大小更为接近的行星。而且他还指出，将来绕轨道运行的望远镜也许能够拍到清晰的行星图像，可以明显地与其恒星区别开来，因此可以用来搜寻生命的迹象。