“逃出”太阳系：旅行者1号踏上星际旅程(有声)

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        MELISSA BLOCK, host: It has spent 33 years traveling nearly 11 billion miles from the sun at a rate of about 38,000 miles per hour, sending back spectacular images of the planets and their moons. And now the space probe Voyager 1 is poised to cross the outer edge of our solar system and venture into interstellar space. We say, poised, meaning in about four years.
        The astrophysicist Neil deGrasse Tyson joins us to talk about that impending transition. He directs the Hayden Planetarium at the American Museum of Natural History in New York. Welcome back to the program.
        Dr. NEIL DEGRASSE TYSON (Director, Hayden Planetarium): Happy to be with you.
        BLOCK: This is the farthest any spacecraft has gone by far, right?
        Dr. TYSON: Mm-hmm.
        BLOCK: NASA announced this yesterday, the Voyager 1 will be leaving the region called the heliosheath（日鞘）. What does that mean?
        Dr. TYSON: Well, there's a boundary between what we call the heliosphere, and that's the region of influence that the sun has over its environment. The sun has a wind. You might've heard of that before - the solar wind. That's what makes the aurora borealis（北极光）. These are particles from the sun that are charged, and when they hit the earth's atmosphere they collide with the atmospheric molecules and render them aglow.
        Well, this stream of particles doesn't just stop at earth, it goes out to the outer reaches of space. And you reach a point where particles from the sun are no longer distinguishable from random other particles traveling throughout the galaxy. And that's the realistic edge of the sun's influence out there. And that's where Voyager 1 is approaching.
        BLOCK: And once Voyager 1 leaves the sphere of influence of the sun and goes out into interstellar space, what do you think astrophysicists like yourself might be learning from it?
        Dr. TYSON: Well, first of all, the transition from being within the heliosphere of the sun to being outside of it is itself an interesting boundary. There's still a lot of interesting measurements that can be made there. Once you're completely beyond it, then you're - that's it, the sun is no longer really operating on you.
        And once you're outside the zone, it's not clear whether things will change much for you because you're kind of wandering
        BLOCK: Will Voyager 1 still be sending information back once it's crossed into interstellar space?
        Dr. TYSON: Yes. It has some - while it's not undergoing any kind of propulsion at the moment, it still has a way to generate electricity. And it's that small amount of electricity that it uses to communicate back and forth with us. So there's no reason why we couldn't keep talking to Voyager well into the next decade.
        BLOCK: I read this from the former mission design manager of Voyager, calling it the greatest mission of discovery in the history of mankind. What do you think we've learned from Voyager 1 that's so spectacular?
        Dr. TYSON: I might be a little biased, but I have to agree that because it wasn't just a mission to one planet, it was a mission to many. It was carefully conceived to be a sort of multi-cushion pool shot from one planet around to another planet. And it was sort of a grand tour of the outer solar system. And then it continued beyond.
        For me, it told me that the moons of planets can be as interesting or more interesting than the planets themselves. These planetary missions, on the flybys that they executed, got good close-up images of Europa and Io and Titan and Ganymede. These are the names of moons around Jupiter and Saturn. And when you see them, they have volcanoes and ice sheets and lakes and you say, my gosh, it's not just this big ball of gas out there, they're surrounded by worlds.
        And when we think of a world, you think of a place you might want to visit. And so I think of the solar system differently in the era of Voyager than I did before.
        BLOCK: Well, Neil deGrasse Tyson, thanks so much.
        Dr. TYSON: Happy to be with you again.
        BLOCK: Astrophysicist Neil deGrasse Tyson directs the Hayden Planetarium at the American Museum of Natural History in New York. He's also author of the book "The Pluto Files: The Rise and Fall of America's Favorite Planet."
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        美国国家航空航天局“旅行者”1号太空探测器发回数据显示，探测器进入一个朝太阳系外方向太阳风风速为零的区域，意味着探测器朝着太阳系边缘又迈进一步。研究人员推算，“旅行者”1号4年后可完全脱离太阳系，进入星际空间。
        周围太阳风风速减为零
        美国航天局位于加利福尼亚州的喷气推进实验室“旅行者”项目科学家埃德·斯通确认：“太阳风已经（向太阳系边缘两侧）偏转，‘旅行者’1号接近星际空间。”
        研究人员今年6月发现探测器周围太阳风风速减为零，当时探测器距太阳约170亿公里。研究人员未立即下定论，而是继续观察4个多月，最终确信探测器周围指向太阳系外方向的太阳风速率的确已减为零。
        测算太阳风速率的方法是，探测器在飞行过程中，测定撞击探测器的带电粒子速率，由相对速度推断太阳风绝对速率。当测算到的相对速度等于探测器飞行速度时，表明太阳风带电粒子在探测器飞行方向上处于静止状态。
        探测器一直向太阳系边缘方向飞行。现有数据结果显示，2007年8月时，探测器周围太阳风速度为每小时21万公里，后来每年大约放慢7.2万公里，自今年6月开始在探测器飞行方向上保持为零。
        按美国航天局说法，探测器进入这个区域是“旅行者”1号离开太阳系过程中一个重要里程。
        长时间运行令科学家惊奇
        研究人员相信，“旅行者”1号仍未进入星际空间，按现阶段估计，完全脱离太阳系大约在4年后。
        研究人员会用模型计算最新数据，更准确地推断“旅行者”1号告别太阳系的时间点。
        探测器一旦飞离太阳系，它周围的热粒子密度会急剧下降，冷粒子密度迅速增加。“旅行者”项目另外一名科学家罗布·德克尔对“旅行者1号”在飞行33年后进入太阳风速度为零区域感到惊奇：“‘旅行者’连续运行33年，仍在向我们提供全新情况。”
        携带唱片准备“问候”外星生命
        “旅行者”项目科学家斯通告诉英国广播公司记者：“发射‘旅行者’时，（美国）航天时代的历史只有20年，（当时）并不知道航天器能持续运转这么久。”“旅行者”1号1977年9月5日升空，“旅行者”2号比它早数日启程。
        脱离地球进入太空后，“旅行者”1号时速6.1万公里，“旅行者”2号时速5.6万公里，两者飞行方向相反。
        美国航天局送两个“旅行者”上天的最初目标是探测木星、土星、天王星和海王星。1989年两个探测器完成既定目标后，继续借助同位素温差发电机 作为动力来源，向太阳系边缘探测，并定期向地球发回数据。随着越来越远离地球，数据回传时间越来越长，现阶段数据回传大约需要16个小时。
        两个探测器各自携带有一张铜质镀金唱片，其中刻写有反映地球生命和文化的声音和图像，以及55种语言念读的问候语，专为“旅行者”旅行途中可能遇到的其他生命准备。