百科知识视频之煎蛋小学堂45 世界末日，人类如何自保？

The sun is around 4.5 billion years old.And just like you and I,it's aging,In just over a billion years,the sun will expand it so much that the heat will begin to melt the earth's surface,So,is there any way as earth things can avoid this detrimental event?Can we save ourselves from the sun's ultimate death?

太阳已有大约45亿岁了。正如你我一样 它也在衰老。在10亿年后 它将变得巨大 它带来的热量会融化地球表面。地球生物怎么才能躲过这次致命的打击?在太阳消亡时我们能否自保?

Sure,none of us would be here,assuming we don't find the secret to everlasting life.but at the billion year mark,the sun will have used up the hydrogen fuel in its core,forcing it to burn at its surface.The increase radiation will boil away all of the water on earth,creating an international desert.

当然 如果没发现长生不老的秘诀 我们活不到那时候。但十亿年后 太阳将会耗尽其内核所有的氢燃料，迫使其在表面燃烧。不断增强的辐射会蒸发干地球上所有的水分，造出洲际沙漠。

Flash foward about 5 billion years,and the swelling sun will bigin literally melting mountains with most,if not all life on earth,now extinct.Around 7.5 billion years,the expanding sun,now a red giant,will engulf the earth entirely,Sounds bleak,so can we avoid this hot mass?

再向后50亿年 巨大的太阳开始将融化山脉 而地球上绝大多数生物早已灭绝。75亿年后 不断膨胀的太阳已成红巨星，并将完全吞噬地球。听起来很吓人 那我们能躲过这团热球吗?

It turns out,our best bet lies something called gravity assist.a technique we have been using for years only to launch space craft through our solar system.Any time a space craft or satellite comes in close proximity to a planet,Cravity grabs hold.And if the spacecraft arrives at the perfect angle,it's able to use some of the planet velocity to catapult it further into space.This extra energy comes from the planet's own enery of motion around the sun.

实际上 我们最有利的赌注在于引力助推。一种多年来 我们只用在向太阳系内发射航天器的技术。当飞行器或卫星靠近行星时，重力会抓住它。如果飞行器的角度刚好合适，它可以利用行星的速度将自身推到宇宙更远。多余的能量来自于行星绕太阳旋转时自身的动能。

But as Newton famously said,To every action,there's an equal and opposite reaction.As the spacecraft uses the earth's gravity to speed up and move towards the earth,the planet will ever so slighty slow down and move toward the spacecraft.Of course,the spacecraft's mass is so small comparatively that it gets launched incredibly far while the planet experience little change.

但正如牛顿所言 每个作用力都存在与之大小相等 方向相反的反作用力。当飞行器利用地球引力加速 向地球靠近时，地球的速度会略有下降 并向飞行器靠近一点。当然 相比之下飞行器的质量太小 以至于卫星可被发射到极远处 而行星却丝毫未变。

But,if we were to increase the spacecraft's size,or use an asteroid,we could potentially move the earth's orbit away from the sun.This would take millions of years and involve large objects coming just close enough to not collide with earth.But,hey,we're got a billions years ahead start.It may seem far fetched,but it's already happening.

但是 如果能让飞行器变大 或者利用小行星，我们就可以让地球轨道远离太阳。这需要数百万年时间，并得让足够大的物体离地球够近 却不能撞到地球。但是 我们还有好几十亿年时间呢。看上去很遥远 但这已经在发生了。

On Oct,9,2013,earth will be used up to gravity assist a spacecraft called Juno which is on its way to Jupiter,As Juno flies within 559 km of us,it will use earth's gravity as the slingshot to boost its velocity by 7.3km/s.Meanwhile,earth will have been moved by a fraction.Juno will later arrive at Jupiter in 2016,where it will study the interior of the planet and help to unveil many new spectacular mysteries of our solar system.

在2013年10月9日 地球将为一颗名叫“Juno"的航天器做引力助推 后者正向木星前进。当Juno飞到距我们559千米处时，地球引力将是它的弹力 它将借此加速到7.3km/s。与此同时 地球仅被移动了一点点。Juno将在2016年抵达木星。在那里 它会研究行星的内部 并帮助我们揭秘关于太阳系的诸多精彩谜题。

In order to move the earth within our billion year's time line,we would need approximately one encounter every 6000 years,using an object with a mass of approximately 10^19 kilograms.That's 0000,0000,0000,0000,000.Some are around the size of 100 kilometer wide asteroids,In between passes,the asteroid would slingshot around the sun,fly up to Jupiter and be gravity assisted back to the earth.Like one long version of catch between planets.

为了在这十亿年间移动地球，我们大约得每6000年一次 用一个质量大约为10^19千克的物体。就是0000，0000，0000，0000，000.某些直径100千米的小行星差不多的东西。在中间穿过时 小行星绕太阳绕太阳加速，飞到火星 之后又被引力助推回地球。正如长距版的星际抛球。

Over millions of years,this would move the earth to a comfortable 225 million km orbit out from the sun.While it is feasible,even with today's technology,it doesn't come without risks.For one,we may lose the moon,which could ultimately create some extreme weather patterns.Not to mention,the earth's spin may increase,making days only hours long,The surrounding planets like our new neighbors,Mars,would likely have their own orbits disstabilized.

几百万年后 地球将因此而移动到安全距离 距太阳 2.25亿公里的轨道。而即使计划可行 凭借今天的科技 这种方式仍有风险。其一 我们会失去月亮。这终将导致某些极端天气模式。更不用说地球自转的速度也将加快 每天都只有几小时。我们周围的新邻居 如火星，他们的轨道会变的不稳定。

You know,the asteroid could come plummeting into earth by accident.But perhaps these other risks we need to take to give our decedents,the planet,and all life on it,a few extra billions of years.

你知道 小行星也会偶然间砸向地球表面。不过 我们可能得把这些风险留给我们的子孙了 一颗行星 其上所有的生命 还有几十亿年。