地球的未来是金星？Future of the Earth is Venus?

最近，我们的红色邻居 - 火星，可是个热门度假胜地啊！

Our red neighbour - Mars has been busy a holiday destination lately! 

2月9日，阿联酋的“希望号”成功进入火星轨道，除夕前夜中国的“天问一号”也随后进入轨道，这周四更是有美国的“毅力号”来凑热闹。全世界的科学家们迫不及待想要挖掘这颗红色星球的更多潜力。

With the United Arab Emirates’ Hopeentering Mars’ orbit on the 9th Feb, China’s Tianwen entering the orbit the day before Chinese New Year eve and America’s Perseverance rover joining later this week, scientists are all excited about exploring the potentials of the Red Planet.

这三项任务都是在2020年7月发射的，目的是发现这颗行星是否曾经或未来适合居住。到达的时间取决于地球和火星围绕太阳的运行轨道，火星足够靠近地球机会每26个月才会有一次，而且只有一个月。

All three missions were launched in July 2020, set out to find whether the planet was ever habitable or will be in the future. The timings of the arrivals are dependent on the Earth’s and Mar’s obits, since there is only a one-month time window every 26 months for Mars to be close to Earth.

但作为我们的另一个邻居 - 金星，它与地球的距离只有火星的2/3，为什么大家都更执着于更远的那颗呢？

But what about our other neighbouring planet - Venus, with about only 2/3 the distance away from Earth compared to Mars, why are we more interested in missions on the planet further away? 

‘错峰出行’作为假期的第一准则，金星还是很值得一看的。不但大小与地球相似，岩石材料也大同小异。更何况目前金星和火星是唯一人类有可能到达的两颗类地球行星，除了他们，最近的‘地球’在12光年以外！

Keeping in mind ‘peak shifting travel’ during the holidays, Venus is well worth seeing. Not only in a similar size to Earth and it is also made roughly with the same rock materials. What's more, Venus and Mars are currently the only Earth-like planets that humans have a chance of reaching. Other than them, the nearest 'Earth' is 12 light-years away！

那今天我们就来看看《人类太空作死榜》的第三位 – 金星吧！（Top 1 = 月球，Top 2 = 火星）

So today, let's take a look at the third place in the ‘Best Places to Visit in Space’ list-- Venus! (Top 1 = the Moon, Top 2 = the Mars)

图为中国‘天问一号’围绕火星的轨道示意图

The planned track of China's 'Tienwen' around Mars

隔壁的桑拿房

The Sauna Next Door

此刻，由于失控温室效应，金星的表面温度达到470摄氏度，热到足以融化铅！而且其大气密度是地球的50倍，完全不适合居住。

Venus now has a surface temperature of 470 Celsius due to its runaway greenhouse effect, hot enough to melt lead and an atmosphere 50 times denser than Earth, making it completely uninhabitable.

不过，金星的大小和地球相似，岩石材料也大致相同，它是否曾经有过地球一样环境呢？也许它也有过汪洋大海，而非干燥的山脉、峡谷和极厚的二氧化碳大气？它会是地球的未来吗?

However, Venus being in similar size to Earth and made roughly with the same rock materials, could it have once upon a time been a planet, just like the one we are standing on? Potentially having an ocean rather than just bone-dry mountains, valleys and a punishingly thick CO2 atmosphere? Could it be the future of Earth?

要回答这些问题，首先必须知道另一个问题的答案：金星上的水从何而来？表面是否有过足够的水，哪怕只是用来形成湖泊的呢?

To answer these questions, another question has to be asked first: where did the water on Venus come from? And was there ever enough to form even lakes on the surface?

图为NASA的麦哲伦号飞船和先锋金星轨道器的火星数据合成图

Images of the composition of data from NASA's Magellan spacecraft and Pioneer Venus Orbiters

冒着泡儿的海

The Bubbling Ocean

类地行星在生命开始时是一团围绕恒星飞行的碎石堆，最初由尘埃和岩石组成，最终慢慢形成原行星直到‘成年’定型。由于这些物质互相碰撞和放射性衰变，它们会产生热量，并将行星融化，分离成密度较大的内核和密度较小的岩石外层。

Terrestrial planets start their lives as rubble piles flying around the star, first as collections of dust and rocks, and eventually forming into protoplanets until reaching their full size. Due to all the impacts and radioactive decay of the materials, heat would be produced, which melts and separated the planet into a dense core and a less dense rocky outer layer.

这时，热到冒泡的岩石海不仅会在冷却时释放气体到大气中，还会与大气中的氧气和水蒸气发生反应，将它们困在表面矿物质中。

This bubbling rocky ocean not only release gases into the atmosphere as it cools, but also react with the oxygen and water vapour in the atmosphere, trapping them in the minerals.

最后，行星的大气层是由火山爆发的和来自太空的水和挥发性气体重建的。而来自外太空的气体很大一部分可能来自星球形成初期陆续着落彗星或陨石。对地球来说，它们的点睛之笔为我们来带了最终质量的0.5% - 1.5%。因此，行星科学的一个关键部分就是充分了解这些事件是何时发生的，以及它们是否从太阳系外为行星带来了额外的水。

The planet’s final atmosphere is rebuilt by its volcanic eruptions and the water and volatile gases from space, which could be from arrival of comets or meteorites. For the Earth, they added the final 0.5–1.5 % of the planet’s final mass. Therefore, a key part in planetary science is to find out when those events took place and whether they brought extra water from outer Solar system.

图为欧洲航天局的'金星快车'在飞行操纵期间的可视化

Visualisation of ESA’s Venus Express during the aerobraking manoeuvre

最近，为了回答关于金星的这些问题，一组欧洲科学家利用了金星现在的大气数据来测试不同时期的不同天体着陆对金星表面的影响，并通过这些数据研究了大气的长期演化。

So recently, to answer these questions in the case of Venus, a group of European scientists used present day atmospheric measurements to test the effects of different late accretions, and through it investigated the long-term evolution of Venus’ atmosphere.

研究小组假设在没有任何天体到达之前，金星大气的初始条件是干燥无氧的。这是因为早在岩浆海阶段，行星就通过非常有效的化学已经把大气中的氧气和水都抽干了。

The team assumed initial condition of accretion-free Venus atmosphere to be dry and oxygen-free. This is because the planet is thought be very effective at removing oxygen and water from the atmosphere via chemical reactions when it was in the magma ocean.

然后，小组利用数学模型模拟了固定质量的陨石撞击表面对行星的影响。模拟中包括了不同陨石的类型（水含量）以及撞击的时间，以观察这些条件对最终水含量的影响。

Then, mathematical models were used to simulate the effect of fixed mass meteorites crashing onto the surface planet.  The team varied the types of meteorites (i.e. dry vs. wet rich) as well as the time of impact to see how those conditions would impact the water levels.

图为前苏联的'金星13号探测器'于1982年3月着陆时拍摄到了金星表面

The surface of Venus captured from the former Soviet Union’s Venera 13 spacecraft, which touched down in March 1982

不太平的水

The Busy Water

遗憾的是，当水到达金星时，它不会有机会停留在原型。首先它会因为表面的高温变成水蒸气，然后在太阳的紫外线辐射下分解成氢和氧。即使太阳几十亿年前没那么活跃，水仍然会分解，因为这些粒子将与上层大气——外逸层发生碰撞；然后可能会被太阳风从行星大气中移除。

Unfortunately, water does not get to stay as it is when it arrives on Venus. It first turns into water vapor and then split into hydrogen and oxygen by Sun’s UV radiation. Even though the Sun would have been less active back then a few billion years ago, the water would still be disintegrated. The particles would collide with the upper atmosphere - the exosphere; then potentially get removed from the planetary atmosphere by the solar wind.

由于这种效应，对行星演化的研究变得更加困难了。作为一个多学科的研究领域，它需要在统计力学、流体力学、等离子体物理、碰撞理论和表面科学等广泛学科的专业知识，使得行星学往往变得扑朔迷离。

Due to this effect, research on planetary evolution is made much more difficult. It is a multidisciplinary research field that requires an expertise in a wide range of subjects including statistical mechanics, fluid mechanics, plasma physics, collision theory, and surface science, adding uncertainties.

所以，在这些过程中，较轻的氢原子会被再次被推入太空，离开它们的老搭档——氧，任其留在金星的大气中。

So, from these processes, the lighter hydrogen atoms would be boosted into the space again, leaving their ex-partners - the oxygens back in the atmosphere.

然而，从到金星之前的各种研究上来看，今天在其大气中只能检测到少量的氧气。因此，研究小组试图预测在过去的45亿年间，也就是从金星结束岩浆海阶段到现在的时间时间段里，大气在演变后可能遗失多少氧气。

However, from various mission to Venus, only little amounts of oxygen were detected in its atmosphere today. So, the team tried to predict how much oxygen could have left Venus over in the last 4.5 billion years, which is from when Venus ended its magma ocean stage to the present day. 

模拟中不仅考虑了太阳辐射在这期间的变化，还包括了火山向大气中添加二氧化碳和氮所导致大气压力的变化。

The modeling also took into account the possible changes of the Sun’s radiation, and the planet’s atmosphere pressure changes as its volcanos add carbon dioxide and nitrogen into atmosphere mixture.

最终，金星失去的氧气越多就会表明它从陨石中获得的水就越多。

The expected results would simply be the more oxygen Venus was able to lose, the more water it received from meteorites.

图为2006年5月16日，欧洲航天局“金星快车”上的可见光和红外热成像光谱仪(VIRTIS)获得了金星南半球的图像。夜侧半球(红色部分)是由1.74微米拍摄的红外图像组成，显示了行星表明45公里高度的云层下层。日面半球(蓝色部分)则是由480纳米的紫外线图像组成的，显示了大约65公里高度的云层顶部。

The southern hemisphere of Venus as a mosaic of images obtained by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board ESA’s Venus Express on 16 May 2006. The night-side hemisphere (in red at the top) is made of infrared images taken at 1.74 μm, showing the lower layers of the cloud deck surrounding the planet at about 45-km altitude. The day-side (in blue at the bottom) is made of ultraviolet images taken at 480 nm, showing the cloud top layer at about 65-km altitude.

干到‘裂开’

About to Crack

模拟的结果令人惊讶，金星在向太空输出氧气方面的实力其实相当的差。数据显示，要么到达的陨石要么含水量都只有2.5%，要么都是在金星两岁之前到达的，不然金星不会有足够的时间消耗掉那么氧气。

Results from the modeling came as a surprise, Venus is actually quite bad at losing oxygen to space. It indicates that the meteorites arrived were either all 97.5% dry or all got there in first 2 years of Venus’ lifetime for the planet to have enough time to get rid of all the oxygen.

金星这辈子消耗的水量仅仅是今天地球表面的水的十分之一。也就是说，也许金星从来都是一颗干燥的星星，从来没有过地球上的环境，甚至根本不适合任何生物居住。

The absolute maximum amount of water lost by Venus over time is only 1/10 of water on Earth’s surface today. This means that Venus might have always been too dry to have Earth-like conditions, or even habitable at all.

图中显示了金星生命周期中可能增加到大气中的水量。黑色显示了由氧气流失到太空后剩下最多的水量。蓝色和紫色显示了金星大气中的水和氧气在被不同的陨石撞击后的变化。锯齿状的红色曲线显示了只有干陨石撞击金星的情况。

Diagram shows the amount of water Venus could have had added to its atmosphere during its lifetime. The black shows the max amount of water that can be accounted for by loss of oxygen to space. The blue and purple  show what happens to the water and oxygen in Venus’ atmosphere after being hit by different meteorites. The jagged red curve shows the situation when only dry meteorites hit Venus.

但这一数据并不能完全排除金星上存在生命的可能性。对金星早期气候的研究表明，即使金星表面含水量极少，也仍然有机会达到适宜居住的条件。

But this data does not completely rule out the possibilities of life existence on Venus. Studies on Venus’ early climate suggest that habitable conditions might still have attainable even with the tiny amount of water available at the surface.

话虽如此，金星上氧气的消失还有其他可能的原因。其中之一就是把铁变成铁锈。金星形成的初期，它完全被富含铁的熔岩流所覆盖的，而这些熔岩很容易与水发生化学反应并吸取所有的氧气。

With that said, there are also other possible reasons for the disappearance of oxygen on Venus. One of them being turning iron into rust. Venus was absolutely covered in rich iron lava flows, which can easily react with and trap all the oxygen from water in the early times of Venus.

不管怎样，现在证明金星过去、现在和将来都不会是最好的度假目的地，那希望就都托付给火星上的新发现吧！祈愿在我们找到下一个家园之前，地球不会变成一个颗金星似的行星，虽然我们现在所有的污染都在加快这件事的发生。

Proven that Venus was and will not be the best holiday destination, hopes lye on the new findings on Mars and that Earth will not turn into a Venus-like planet before we find our next home, which we are encouraging it now with all the pollutions.

在漫长的太空历险探索期间，

我们能做到最好的支持就是

保住现在的饭碗，

别吃着碗里的，看着锅里的！

During these long space adventures, 

the best support we can offer 

would be to keep our mother Earth 

as healthy as she can be!

图为太阳风暴袭击火星时从火星高层大气中剥离离子的艺术绘画

Artist’s rendering of a solar storm hitting Mars and stripping ions from the planet's upper atmosphere.

天体图片来自 NASA, CGTN, ESA 官网以及以下论文

文中部分英文信息参考来自德国、比利时、法国和瑞士学者合作， 由 C. Gillmann 带领的团队的 “Dry Late Accretion inferred from Venus” coupled atmosphere and internal evolution" 论文

其余中英文内容为原创

Stellar images from official website of NASA, CGTN, ESA and the below article

Parts are from “Dry Late Accretion inferred from Venus' coupled atmosphere and internal evolution" by the scientist team lead by C. Gillmann from Belgium, Germany, France and Switzerland

The rest of the Chinese and English content is original