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科学家发现新的类地行星

所属:社会热点 作者:颜麦粥 来源:National Geographic 阅读:3381 次 评论:0 条 [我要评论]  [+我要收藏]

小编摘要:人类向宇宙的探索不曾停止,一项新的研究称,最新发现的一颗距离地球大约36光年的行星可能是跟地球最类似的行星之一,前提是那个行星上有足够的云层。

导读:一项新的研究称,最新发现的一颗距离地球大约36光年的行星可能是跟地球最类似的行星之一,前提是那个行星上有足够的云层。研究发现该行星绕行在帆船座的一颗橙矮星的轨道上。高精度径向速度行星搜索器(HARPS)收集的数据显示,这颗行星的质量是地球的三倍,它与其绕行恒星的距离刚好可以使得其星球表面的水呈液态,而这一点对人类生活是非常重要的。新类地行星到恒星的距离比金星到太阳的距离稍远,会比地球吸收到更多的太阳能。到目前为止,这颗新类地行星是太阳系之外第二个在其可居住地区里有岩石的新世界,在这个可居住的区域里温度足够适宜使水保持液态。之前发现的另一颗行星则在该恒星可居住区域里偏冷的边界区。受太空旅行的限制,目前人类仍无法访寻新类地行星。 

A new planet found about 36 light-years away could be one of the most Earthlike worlds yet—if it has enough clouds, a new study says.

The unpoetically named HD85512b was discovered orbiting an orange dwarf star in the constellation Vela. Astronomers found the planet using the European Southern Observatory's High Accuracy Radial velocity Planet Searcher, or HARPS, instrument in Chile.

Radial velocity is a planet-hunting technique that looks for wobbles in a star's light, which can indicate the gravitational tugs of orbiting worlds.

The HARPS data show that the planet is 3.6 times the mass of Earth, and the new world orbits its parent star at just the right distance for water to be liquid on the planet's surface—a trait scientists believe is crucial for life as we know it.

"The distance is exactly the limit where you want to be to have liquid water," said study leader Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics and the Max Planck Institute for Astronomy.

"If you scale it to our system, it's a bit further out than Venus is to our sun." At that distance, the planet likely receives a bit more solar energy from its star than Earth does from the sun.

But Kaltenegger and colleagues calculate that a cloud cover of at least 50 percent would reflect enough of the energy back into space to prevent overheating.

On average, Earth has 60 percent cloud cover, so partly cloudy skies on HD85512b are "not out of the question," she said.

Of course, clouds of water vapor depend on the presence of an atmosphere similar to Earth's, something that can't be detected on such distant planets with current instruments.

Models of planet formation predict that planets with more than ten times Earth's mass should have atmospheres dominated by hydrogen and helium, Kaltenegger said. Less massive worlds—including HD85512b—are more likely to have Earthlike atmospheres, made mostly of nitrogen and oxygen. 

New World "A Strong Candidate" for Habitability  

So far, the newly detected planet is only the second rocky world outside our solar system to be confirmed in its star's habitable zone—the region around a star that's not too hot and not too cold for liquid water.

The other contender, planet Gliese 581d, was previously discovered using the HARPS instrument. This world lies just on the cool edge of its star's habitable zone.

Another promising planet, Gliese 581g, was discovered in 2010 and dubbed the most Earthlike planet yet. But controversy surrounds the claim, with some experts declaring that the entire planet is actually a data glitch.

Manfred Cuntz, director of the astronomy program at the University of Texas, Arlington, noted that more information is needed before anyone can speculate whether aliens are wandering around the newfound planet.

"It's not their fault no extra information [about the planet's atmosphere] is available right now," Cuntz said of the research team. "It looks like this is a strong candidate, in principle."

In addition to size and location, HD85512b has two other points in its favor for potentially harboring life, Cuntz said.

The planet's orbit is nearly circular, which would provide a stable climate, and its parent star, HD85512, is older—and therefore less active—than our sun, which would lower the likelihood of electromagnetic storms damaging the planet's atmosphere.

Not only that, but in principle, the age of the system—5.6 billion years—"gives life a chance to originate and develop," he said. By contrast, our own solar system is thought to be about 4.6 billion years old. 

New Planet a Great Place for Yoga?

Given current limits on space travel, it's unlikely for now that humans will get to visit HD85512b.

But if we could get there, the newfound planet might seem like a fairly alien world: muggy, hot, and with a gravity 1.4 times that of Earth's, study leader Kaltenegger said.

On the bright side, "hot yoga might be one of the things you don't have to pay for there," she quipped.

The paper describing HD85512b appears online at arXiv.org and has been accepted for publication in the journal Astronomy and Astrophysics

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2011-09-01 20:19 编辑:颜麦粥
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