飞过冥王星8个月后 科学家都发现了什么？
就在一年前，冥王星还是新视野号相机镜头里不起眼的明亮斑点，与1930年克莱德·汤博发现它时没什么两样。
但就在这一周的《科学》杂志上，新视野号团队的科学家们发表了第一套综合性论文，来描述去年7月新视野号近距离飞掠冥王星系统得到的最新探测结果。
来自美国西南研究院(SwRI)、新视野号首席科学家阿兰·斯特恩（Alan Stern）介绍说：“这五篇论文完全改变了以往我们对冥王星的认识，新视野号揭示这颗“前第九大行星”是一个拥有多种地貌、地质活动相当活跃的星球。冥王星表面物质成分令人惊异，且有一个与太阳交互作用复杂的大气层，以及一群有趣的小卫星。”
去年7月14日，在深空飞行9年，旅途长达30亿英里（近50亿公里）的新视野号抵达了它最重要的目标天体--冥王星。新视野号也是迄今从地球出发速度最快的探测器，离开地球时速度达到16.26千米/秒，在发射后9小时就飞过了月球轨道，而阿波罗飞船需要三天。
新视野号携带的七项仪器获得了冥王星约50Gb的科学数据，这些数据绝大多数是在飞掠前后九天的时间里获得的。
冥王星的第一张近距离照片显示了其表面拥有一个巨大的“心形”地貌特征，向科学家展示了这颗矮行星的冰封世界。这也是人类首次“涉足”这片遥远的太阳系边缘地带--柯伊伯带，而冥王星正是柯伊伯带里迄今发现的最大的天体，这些天体比之前我们建立模型预测的更有趣，也更令人迷惑。
在这之前，科学家们认为柯伊伯带的天体自形成以来应该变化不大。但新视野号近距离观测冥王星与冥卫一卡戎（Charon）的结果却让科学家不得不重新思考，究竟什么样的地质活动可以在这些遥远的天体上持续这么久。
通过分析冥王星表面物质的成分，科学家们认为今天冥王星复杂多样的地貌，源自亿万年来冥王星表面物质的持续相互作用。这些物质包括易挥发移动的甲烷冰、氮冰与一氧化碳冰，以及在冥王星低温表面较稳定的水冰。
来自洛厄尔天文台的科学家、论文第一作者威尔·格兰迪（Will Grundy）介绍说：“我们注意到表面易挥发冰类物质的分布变化，这说明冥王星有奇妙的挥发-冷凝循环过程。相比较地球上的水循环，冥王星的这个物质循环过程更丰富，至少有三种物质参与，并且这个相互作用过程我们现在还没有弄明白，但是我们肯定它们的相互作用让冥王星整个表面发生了变化。”
科学家们也发现冥王星上空分层的雾霭状大气，并且大气层比预期更冷更稠密，这影响到冥王星的上层大气如何逃逸到宇宙空间，以及如何与太阳风中的带电粒子流相互作用。
在这之前，科学家认为从冥王星大气逃逸损失的物质会非常多，就像彗星挥发的彗尾一样。但实际上，冥王星大气物质逃逸速度并不快，反倒和我们地球大气层很相似。科学家们发现冥王星大气逃逸的气体主要是甲烷，而不是氮气，这是相当令人惊讶的，因为冥王星近表大气有99%的组成是氮气。
科学家也对冥王星的四颗小卫星进行了首次近距离成像分析，这些卫星是在2005年至2012年间发现的。其中冥卫二尼克斯（Nix）和冥卫三许德拉（Hydra）直径约40千米，冥卫四科伯罗司（Kerberos）与冥卫五斯堤克斯（Styx）直径约10千米。科学家发现这些小卫星有异常高且不规律的旋转速度，以及不寻常的极向一致性。这些卫星都有明亮的冰层表面，且颜色与冥王星和冥卫一卡戎很不一样。
有证据证明其中几颗小卫星是由早期更小的碎片合并而成，并且表面地质年龄至少已有40亿年。这两条探测结果支持科学家此前对这些小卫星形成的假设：在冥王星-冥卫一双星系统形成期间，这些小卫星由很多碎片碰撞形成。
目前，科学家已接收到一半新视野号飞掠冥王星所获得数据，这些数据以无线电信号的形式光速传回地球需要五个小时，所有冥王星的科学数据将在2016年底全部发回。
以下为新视野号的九大新发现：
01.由表面撞击坑数量计算，冥王星在过去40亿年里一直处于地质活跃状态。此外，冥王星心形区域里光滑的“史泼尼克平原(Sputnik Planum)”没有探测到任何陨石坑，地质年龄非常年轻，不超过1000万年。
02.冥王星最大卫星冥卫一卡戎拥有一个古老的表面。例如，卡戎赤道附近的武尔坎平原(Vulcan Planum)可能是在40亿年前，由大量冰火山的喷发物流动形成的。这些流动的喷发物源自卡戎远古时期的地下海洋，从地壳破裂处喷发出来。
03.冥王星表面物质呈现区域性分布特征：有些区域氮较为丰富，有些甲烷较为丰富，而有些区域水冰分布较为集中，这样的发现已经非常让人惊讶，同时这种分布也为了解冥王星地质历史与气候变化创建了拼图。在外太阳系，冥王星表面的物质变化是前所未有的。
04.冥王星上层大气温度比之前预测的要低很多，这对冥王星大气逃逸速率有重要影响，但为什么冥王星大气层比预想的要冷仍是一个谜。
05.新视野号对冥王星大气中许多重要组成成分（包括分子氮、甲烷、乙炔、乙烯、乙烷）进行了测量，并首次绘制出高度函数。
06.同样也是首次，冥王星雾霾状大气层一种可能的形成机制被发现。这种机制涉及由浮力波影响的大气中混浊颗粒的浓度，由风吹过冥王星山区形成。
07.在飞掠冥王星前，因为发现了其他小型卫星，引发了对冥王星系统中可能存在冰与岩石碎片的担忧。但是新视野号携带的尘埃计数器在飞掠前五天内，只发现了零星的尘埃粒子，这表明冥王星周围区域实际上不是充满了碎片。
08.新视野号揭示了太阳风和冥王星大气之间的相互作用区域，在向着太阳的一面只有7000公里，不到冥王星半径的6倍，这比之前预期的要小的多。这可能是因为冥王星大气逃逸速率低于此前建模得到的结果，而之前建立的模型源于对冥王星紫外大气掩星的观测数据。
09.冥王星四颗小卫星拥有较高的反照率，大约50%~80%。这与柯伊伯带上其他小天体较低的反照率非常不同，其他小天体反照率只有5%~20%。这说明了这四颗小卫星并不是冥王星从柯伊伯带里俘获的，而是在早期形成整个冥王星卫星系统的过程中，大型撞击产生的物质盘聚合形成。
翻译来自腾讯太空，以下是nasa网站的英文原文：
year ago, Pluto was just a bright speck in the cameras of NASA’s approaching New Horizons spacecraft, not much different than its appearances in telescopes since Clyde Tombaugh discovered the then-ninth planet in 1930.
But this week, in the journal Science, New Horizons scientists have authored the first comprehensive set of papers describing results from last summer’s Pluto system flyby. “These five detailed papers completely transform our view of Pluto – revealing the former ‘astronomer’s planet’ to be a real world with diverse and active geology, exotic surface chemistry, a complex atmosphere, puzzling interaction with the sun and an intriguing system of small moons,” said Alan Stern, New Horizons principal investigator from the Southwest Research Institute (SwRI), Boulder, Colorado.
After a 9.5-year, 3-billion-mile journey – launching faster and traveling farther than any spacecraft to reach its primary target – New Horizons zipped by Pluto on July 14, 2015. New Horizons’ seven science instruments collected about 50 gigabits of data on the spacecraft’s digital recorders, most of it coming over nine busy days surrounding the encounter.
The first close-up pictures revealed a large heart-shaped feature carved into Pluto’s surface, telling scientists that this “new” type of planetary world – the largest, brightest and first-explored in the mysterious, distant “third zone” of our solar system known as the Kuiper Belt – would be even more interesting and puzzling than models predicted.
“Observing Pluto and Charon up close has caused us to completely reassess thinking on what sort of geological activity can be sustained on isolated planetary bodies in this distant region of the solar system, worlds that formerly had been thought to be relics little changed since the Kuiper Belt’s formation,” said Jeff Moore, lead author of the geology paper from NASA's Ames Research Center, Moffett Field, California.
Scientists studying Pluto’s composition say the diversity of its landscape stems from eons of interaction between highly volatile and mobile methane, nitrogen and carbon monoxide ices with inert and sturdy water ice. “We see variations in the distribution of Pluto's volatile ices that point to fascinating cycles of evaporation and condensation,” said Will Grundy of the Lowell Observatory, Flagstaff, Arizona, lead author of the composition paper. “These cycles are a lot richer than those on Earth, where there's really only one material that condenses and evaporates – water. On Pluto, there are at least three materials, and while they interact in ways we don't yet fully understand, we definitely see their effects all across Pluto's surface.”
Above the surface, scientists discovered Pluto’s atmosphere contains layered hazes, and is both cooler and more compact than expected. This affects how Pluto’s upper atmosphere is lost to space, and how it interacts with the stream of charged particles from the sun known as the solar wind. “We’ve discovered that pre-New Horizons estimates wildly overestimated the loss of material from Pluto’s atmosphere,” said Fran Bagenal, from the University of Colorado, Boulder, and lead author of the particles and plasma paper. “The thought was that Pluto’s atmosphere was escaping like a comet, but it is actually escaping at a rate much more like Earth’s atmosphere.”
SwRI’s Randy Gladstone of San Antonio is the lead author of the Science paper on atmospheric findings. He added, “We’ve also discovered that methane, rather than nitrogen, is Pluto’s primary escaping gas. This is pretty surprising, since near Pluto’s surface the atmosphere is more than 99 percent nitrogen.”
Scientists also are analyzing the first close-up images of Pluto’s small moons—Styx, Nix, Kerberos and Hydra. Discovered between 2005 and 2012, the four moons range in diameter from about 25 miles (40 kilometers) for Nix and Hydra to about six miles (10 kilometers) for Styx and Kerberos. Mission scientists further observed that the small satellites have highly anomalous rotation rates and uniformly unusual pole orientations, as well as icy surfaces with brightness and colors distinctly different from those of Pluto and Charon.
They’ve found evidence that some of the moons resulted from mergers of even smaller bodies, and that their surface ages date back at least 4 billion years. “These latter two results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary system,” said Hal Weaver, New Horizons project scientist from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, and lead author of the Science paper on Pluto’s small moons.
About half of New Horizons’ flyby data has now been transmitted home – from distances where radio signals at light speed need nearly five hours to reach Earth – with all of it expected back by the end of 2016.
“This is why we explore,” said Curt Niebur, New Horizons program scientist at NASA Headquarters in Washington. “The many discoveries from New Horizons represent the best of humankind and inspire us to continue the journey of exploration to the solar system and beyond.”
year ago, Pluto was just a bright speck in the cameras of NASA’s approaching New Horizons spacecraft, not much different than its appearances in telescopes since Clyde Tombaugh discovered the then-ninth planet in 1930.
But this week, in the journal Science, New Horizons scientists have authored the first comprehensive set of papers describing results from last summer’s Pluto system flyby. “These five detailed papers completely transform our view of Pluto – revealing the former ‘astronomer’s planet’ to be a real world with diverse and active geology, exotic surface chemistry, a complex atmosphere, puzzling interaction with the sun and an intriguing system of small moons,” said Alan Stern, New Horizons principal investigator from the Southwest Research Institute (SwRI), Boulder, Colorado.
After a 9.5-year, 3-billion-mile journey – launching faster and traveling farther than any spacecraft to reach its primary target – New Horizons zipped by Pluto on July 14, 2015. New Horizons’ seven science instruments collected about 50 gigabits of data on the spacecraft’s digital recorders, most of it coming over nine busy days surrounding the encounter.
The first close-up pictures revealed a large heart-shaped feature carved into Pluto’s surface, telling scientists that this “new” type of planetary world – the largest, brightest and first-explored in the mysterious, distant “third zone” of our solar system known as the Kuiper Belt – would be even more interesting and puzzling than models predicted.
“Observing Pluto and Charon up close has caused us to completely reassess thinking on what sort of geological activity can be sustained on isolated planetary bodies in this distant region of the solar system, worlds that formerly had been thought to be relics little changed since the Kuiper Belt’s formation,” said Jeff Moore, lead author of the geology paper from NASA's Ames Research Center, Moffett Field, California.
Scientists studying Pluto’s composition say the diversity of its landscape stems from eons of interaction between highly volatile and mobile methane, nitrogen and carbon monoxide ices with inert and sturdy water ice. “We see variations in the distribution of Pluto's volatile ices that point to fascinating cycles of evaporation and condensation,” said Will Grundy of the Lowell Observatory, Flagstaff, Arizona, lead author of the composition paper. “These cycles are a lot richer than those on Earth, where there's really only one material that condenses and evaporates – water. On Pluto, there are at least three materials, and while they interact in ways we don't yet fully understand, we definitely see their effects all across Pluto's surface.”
Above the surface, scientists discovered Pluto’s atmosphere contains layered hazes, and is both cooler and more compact than expected. This affects how Pluto’s upper atmosphere is lost to space, and how it interacts with the stream of charged particles from the sun known as the solar wind. “We’ve discovered that pre-New Horizons estimates wildly overestimated the loss of material from Pluto’s atmosphere,” said Fran Bagenal, from the University of Colorado, Boulder, and lead author of the particles and plasma paper. “The thought was that Pluto’s atmosphere was escaping like a comet, but it is actually escaping at a rate much more like Earth’s atmosphere.”
SwRI’s Randy Gladstone of San Antonio is the lead author of the Science paper on atmospheric findings. He added, “We’ve also discovered that methane, rather than nitrogen, is Pluto’s primary escaping gas. This is pretty surprising, since near Pluto’s surface the atmosphere is more than 99 percent nitrogen.”
Scientists also are analyzing the first close-up images of Pluto’s small moons—Styx, Nix, Kerberos and Hydra. Discovered between 2005 and 2012, the four moons range in diameter from about 25 miles (40 kilometers) for Nix and Hydra to about six miles (10 kilometers) for Styx and Kerberos. Mission scientists further observed that the small satellites have highly anomalous rotation rates and uniformly unusual pole orientations, as well as icy surfaces with brightness and colors distinctly different from those of Pluto and Charon.
They’ve found evidence that some of the moons resulted from mergers of even smaller bodies, and that their surface ages date back at least 4 billion years. “These latter two results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary system,” said Hal Weaver, New Horizons project scientist from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, and lead author of the Science paper on Pluto’s small moons.
About half of New Horizons’ flyby data has now been transmitted home – from distances where radio signals at light speed need nearly five hours to reach Earth – with all of it expected back by the end of 2016.
“This is why we explore,” said Curt Niebur, New Horizons program scientist at NASA Headquarters in Washington. “The many discoveries from New Horizons represent the best of humankind and inspire us to continue the journey of exploration to the solar system and beyond.”