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也许生命并不需要水

Maybe Life Doesn't Need Water, After All

前奏
[♪ INTRO]
有许多方法可以在其他星球寻找生命
There are a lot of ways to search for life on other planets,
而且多年以来
and over the years, we’ve
我们已经多次探讨它们
talked about plenty of them,
透过不寻常的光寻找特定的气体
from looking for certain gases to unusual types of light.
但是这些方法多半有一条指导原则:关注水
But for the most part, all those methods aregoverned by one guiding principle: Follow the water.
因为在地球上
That’s because, on Earth,
我们还不知道有哪个物种可以缺水生存
we don’t know of any species that can survive without it.
显然 水非常重要
Water is so important that, by definition,
一个星球的可居住地区条件
the habitable zone around a star
就是有液态水存在
is the area where the conditions are right for liquid water to exist.
但是正如一些研究员指出
But as some researchers have pointed out,
可能我们有点想当然以地球为标准了
there’s a chance that we’re just beinga teeny bit Earth-centric.
毕竟 地球外有许多奇特的化学作用
After all, there’s an awful lot of chemistry out there,
所以可能有一些生命
so maybe there’s some type
可以用其他物质替代水
of life that uses an alternative to water.
这听起来有点荒唐 但是研究者已经开始调查了
It sounds a little ridiculous, but researchers have begun to look into it.
并且他们已经发现这并非不可能
And they’ve found that it might not be impossible.
首先
At first, the idea
没有水有生命存在的观点听起来多么愚蠢 因为水是直接简单
of life without water sounds so silly because water is straight-up amazing.
我的意思是看它的结构
I mean, look at its structure.
水分子是只有两个氢原子和一个氧原子构成的简单分子
Water is a simple molecule of just two hydrogen atoms and an oxygen.
但是正是因为这些原子的排列方式
But because of the way that those atoms are arranged,
分子的一边有轻微的正电荷
one side of that molecule has a slightly positive charge,
另一边是轻微的负电荷
and the other is slightly negative.
这样使水分子是一个极性分子
That makes water a polar molecule.
虽然还有许多其他分子和它一样
And while there are plenty of others like it,
水分子却是特别的
water is special because the difference
因为它的电荷之间的差异是比较大的
between its charges is relatively large.
还有其他原因使得水分子成为很好的溶解物
Among other reasons, that makes H2O reallygood at dissolving things.
它的电荷使水能够和其他物质强烈作用
Its charges allow water to interact
通过紊乱它们分子或原子的化学键
with other substances so strongly that it disrupts the
从而导致其他物质的溶解
chemical bonds between their molecules or atoms, causing the other substance to dissolve.
水可以溶解大量的化合物
And water can do that with a huge range ofcompounds.
它被科学家称为万能溶剂
It’s what scientists call a universal solvent.
强力的溶剂是生命的必需
A powerful solvent is essential for life,
因为生物过程需要
since biological processes require lots of
大量不同分子集于一处
different molecules all in one place.
溶剂使它们混合并相互作用
And solvents allow them to mingle and interact.
虽然这并不是水的唯一好处
That isn’t the only good thing about water,though.
在地球上 水的性能
On Earth, its properties may also have
能让生命首次进化
allowed life to evolve in the first place.
那是因为一些分子
That’s because some molecules can be
普遍能够被水吸引或排斥
generally attracted to or repelled by water.
而且某些物质在同一部位兼具亲水和疏水属性
And certain substances have both water-loving and water-hating parts in the same package.
磷脂就是其中一种
Phospholipids are one of those substances.
为了努力同时接近
In an effort to get close to and away
和远离水
from the water at the same time,
它们把自己组成完美的小泡 叫做囊泡
they’ll organize themselves intonice little bubbles, called vesicles.
这里可以产生微小的化学反应并且不被打扰
That creates tiny pockets of chemistry, where reactions can happen without being disturbed.
这就可能使生命得以出现
And that may have allowed life to emerge.
总的来说
As a whole,
水的结构使它成为强大的生物化学媒介
water’s structure makes it a powerful medium for biochemistry,
就更不用说它的其他性质了
and that’s not to mention all of its other qualities,
比如它能使得一个星球上的温度更加稳定
like the fact that it can keep temperatures on a planet more stable.
但正是因为水在这很重要
But just because water is important here doesn’t
并不意味着水到处都重要
mean it has to be important everywhere.
还有其他分子能够取代水的角色
There are other molecules that can fill someof water’s roles.
拿氨来说 它是一个氮原子连着三个氢原子
Take ammonia, which is one nitrogen atom bondedto three hydrogens.
木星的云层含有丰富的氮
Ammonia is abundant in Jupiter’s clouds,
在土星的卫星土卫二喷出的羽状物中
and it’s also been detected in the
也被检测出有氮
plumes emitted from Saturn’s moon Enceladus.
像水一样 它的原子有电荷差
Like water, it has a charge difference among its atoms,
使它有两极
making it polar.
这就意味着它能溶解许多物质
That means it can dissolve a lot of substances,
包括许多在生化反应中的物质
including many used in biochemical reactions.
但就是因为它的结构和水不完全一样
But because its structure isn’t exactlythe same as water,
它溶解相同物质的效果就不是很好
it isn’t as good at dissolving the same things.
那就意味着地球上的生命
That means life on Earth couldn’t use it
不能够把它当成一个直接替代品
as a direct substitute, but scientists think
但科学家认为
it’s possible that a different kind
一种不同的生命可能已经进化到可以利用它
of life could have evolved to take advantage of it.
那里甚至有亲氮分子和疏氮分子
There are even ammonia-loving andammonia-hating molecules out there,
这些可以产生化学反应的小泡
which could give rise to thosevesicles for chemical reactions.
所以氮是水的一个很好替代品
So ammonia is a promising alternative to water,
但不是最佳的
but it’s not perfect.
它较弱的电荷和互相作用使得化学反应更加困难
Its weaker charges and interactions make chemical reactions just a bit more tough. Plus,
另外 水的沸点是在100摄氏度
while water is liquid over a range
而氮在地球的压力下
of 100 degrees Celsius, ammonia’s liquid range
沸点只有44度
is just 44 degrees at Earth-like pressures.
如果星球的气候波动的话 那么生命的活动空间就会减少
That would give life less wiggle room if a planet’s climate fluctuated.
如果压力越大那么沸点越高
It can stay liquid at higher temperaturesif there’s higher pressure,
像在一个充满气体的巨星中
like in a gas giant,
但是到如今我们还没理解
but right now we just don’t understand how life
生命怎么才能诞生在气体行星的云层中
could get started suspendedin the clouds of a gassy planet.
所以另外一批研究人员认为是碳氢化合物 比如甲烷和乙烷
So another option researchers are considering is hydrocarbons, like methane and ethane.
一般来说 它们都是由碳和氢连接而成
Broadly speaking, these are strings of carbon and hydrogen,
在地球上 它们是天然气的主要成分
and on Earth, they make up natural gas.
但在太阳系的其他更冷的地方
But elsewhere in the solar system,
这些碳氢化合物是液态的
where it’s much colder, these hydrocarbons exist as liquids.
2004年我们发现了最显著的案例
We discovered the most famousexample of this in 2004,
当卡西尼–惠更斯卫星飞行显示
when the Cassini-Huygens mission revealed that the surface
土星的泰坦卫星表面
of Saturn’s moon Titan
被液态碳氢化合物形成的湖泊和海洋覆盖
is covered with lakes andoceans of liquid hydrocarbons.
首先 甲烷看起来
At first, things like methane might seem
并不是水的合理替代品
like a weird substitute for water,
因为他们不是极性分子
because they aren’t polar,
所以它们没有相同的溶解性质
so they don’t have the same power to dissolve things.
但也不是像碳氢化合物一样不可溶
But it’s not like hydrocarbons can’t dissolve anything.
它们可以溶解各种油和脂肪
They can dissolve all kinds of oils and fats,
所以一些反应可能发生
so some reactions would be possible. Also,
当然 一些在DNA中的分子
some molecules, like ones used in DNA,
在碳氢化合物中甚至可能比在水中更稳定
might be even more stable in hydrocarbons than in water.
所以生命可能更容易在那里形成
So maybe it would be even easier for life to evolve there.
科学家们也暗示
Scientists have also suggested that something
像从泰坦这样的地方发现类似囊泡的物体
like vesicles could form in places like Titan,
虽然他们可能用了不同的分子
although they would likely use a different molecule,
这是因为那里没有真的磷脂
since there aren’t really phospholipids there.
所以 虽然以碳氢化合物为基础的生命有点不同
So again, while hydrocarbon-based life might look a bit different,
但也不是完全不可能的
it’s not totally out of the question.
氨和碳氢化合物也不是水的唯一替代品
Ammonia and hydrocarbons aren’t the onlywater alternatives, either.
科学家们也研究了
Scientists have also been studying everything
从液氮到硫酸的全部性质
from liquid nitrogen to sulphuric acid,
而且每样都有存在可能性
and each seems to have some potential. So,
所以 不管怎么说
at the end of the day,
水可能不是生命的必需
maybe water isn’t necessary for life.
在我们能够明确地说这件事之前
Before we can say that for sure, though,
科学家需要多学学生物化学相关知识
scientists will need to learn more about biochemistry,
并且多了解水本身
and more about water itself.
因为一些研究者认为
Because some researchers think we don’t
我们甚至不理解
even understand all of the ways
水作为必需品的所有原因
that water is necessary yet.
不管怎样 一旦我们能够更好理解这件事
Either way, as we start to understand this better,
科学家们可能不得不改变他们评判宜居星球的标准
scientists might have to change whatthey consider a habitable planet.
如果他们这样做
And if they do,
那将真的开启全新领域的研究
that will literally open up a whole new world of study.
感谢观看本期的《太空科学秀》!
Thanks for watching this episode of SciShowSpace!
宇宙中还有许多需要探索 从化学到天体动力学
There’s lots to explore in the universe,from chemistry to astrodynamics,
我们无比感激有机会解读这些知识
and we’re thankful for the chance to unpack so much of it.
感谢我们Patreon的赞助商!
So to our patrons on Patreon, thank you!
如果你支持本节目
And if you want to support the show
帮助我们制作更多这样的剧集
and help us make more episodes like this,
你可以访问 patreon.com/scishow
you can go to patreon.com/scishow.
尾奏
[♪ OUTRO]

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视频概述

在我们认识当中,水是生命的必需。可是事实真的是如此吗?走进《太空科学秀》,或许能找到不一样的答案!

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视频来源

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