For a certain kind of investor, asteroid mining is a path to untold riches. Astronomers have long known that asteroids are rich in otherwise scarce resources such as platinum and water. So an obvious idea is to mine this stuff and return it to Earth—or, in the case of water, to a moon base or Earth-orbiting space station.
对于某种类型的投资者来说，行星探矿是一条通往无限财富的道路。天文学家们早就知道，小行星富含其他稀有资源，比如铂和水。所以投资者们都想开采这些物质并将其运送回地球，或者，要是水资源的话，就送返月球基地或地球轨道空间站。
There is no shortage of interest in these ventures. In the last decade, investors have funded half a dozen companies that have set their sights on various nearby rocks. To many observers, it’s only a matter of time before such a mission gets the green light.
人们对这些商业投资从不缺乏兴趣。过去10年，投资者为6家公司提供了资金，这些公司将目光投向了附近的各种岩石。对许多观察员来说，这样的任务得到批准只是时间问题。
But profit margins are only part of the picture. A potentially more significant aspect of these missions is the impact they will have on Earth’s environment. But nobody has assessed this environmental impact in detail.
但利润空间只是其中的一部分。一个潜在的更为重要的方面是它们对地球环境的影响。但没有人详细评估过这种环境影响。
Today, that changes thanks to the work of Andreas Hein and colleagues at the University of Paris-Saclay in France. These guys have calculated the greenhouse-gas emissions from asteroid-mining operations and compared them with the emissions from similar Earth-based activities. Their results provide some eyebrow-raising insights into the benefits that asteroid mining might provide.
现在，这一变化多亏了法国巴黎萨克莱大学的安德里亚斯·海因（Andreas Hein）和他的同事们的工作。他们计算了小行星采矿工作时产生的温室气体排放量，并将其与类似的地球活动产生的温室气体进行了比较。他们的研究结果为小行星采矿可能带来的好处提供了一些让人惊讶的见解。
The calculations are relatively straightforward. Rocket launches release significant amounts of greenhouse gases into the atmosphere. The fuel on board the first stage of a rocket burns in Earth’s atmosphere to form carbon dioxide. For kerosene-burning rockets, one kilogram of fuel creates three kilograms of CO2. (The second and third stages operate outside the Earth’s atmosphere and so can be ignored.)
计算相对比较简单。火箭发射释放大量的温室气体到大气中。火箭第一阶段的燃料在地球大气层中燃烧，形成二氧化碳。燃烧煤油的火箭，一公斤燃料产生三公斤二氧化碳。(第二阶段和第三阶段在地球大气层之外运行，因此可以忽略不计。)
Reentries are just as damaging. That’s because a significant mass of a re-entering vehicle ablates in the upper atmosphere, producing NOx such as nitrous oxide (N2O), a greenhouse gas that is about 300 times more potent than CO2. By one estimate, the space shuttle released about 20% of its mass in the form of N2O every time it returned to Earth.
重返大气层同样具有破坏性。这是因为重新进入大气层的飞行器中有很大一部分会在高层大气中烧蚀，从而产生氮氧化物，比如一氧化二氮(N2O)，这是一种比二氧化碳强300倍的温室气体。据估计，每次航天飞机返回地球时，其质量的20%会以N2O的形式释放。
Hein and co use these numbers to calculate that a kilogram of platinum mined from an asteroid would release some 150 kilograms of CO2 into Earth’s atmosphere. However, economies of scale from large asteroid-mining operations could lower this to about 60 kilograms of CO2 per kilogram of platinum.
海因和他的同事利用这些数字计算出，从小行星上开采出的一公斤铂将向地球大气层释放约150公斤的二氧化碳。但以大型小行星采矿业务的经济规模来说，开采每公斤铂释放的二氧化碳可从150公斤减少到60公斤。
That needs to be compared with the emission from Earth-based mining. Here, platinum mining generates significant greenhouse gases, mostly from the energy it takes to remove this stuff from the ground.
这需要与地球的采矿排放量进行比较。在这里，铂矿开采产生的大量的温室气体主要来自于从地下开采这些物质所需要的能量。
Indeed, the numbers are huge. The mining industry estimates that producing one kilogram of platinum on Earth releases around 40,000 kilograms of carbon dioxide. “The global warming effect of Earth-based mining is several orders of magnitude larger,” say Hein and co.
事实上，这个数字非常巨大。采矿业估计，在地球上生产一公斤铂会释放约4万公斤二氧化碳。海因及其同事说:“地球采矿对全球变暖的影响要大上几个数量级。”
The figures for water are also encouraging. In this case, the authors calculate the greenhouse-gas emissions from an asteroid-mining operation that returns water to anywhere within the moon’s orbit, a so-called cis-lunar orbit. They compare this to the emissions from sending the same volume of water from Earth into orbit.
水资源的相关数据也同样振奋人心。在这种情况下，作者计算了一项小行星采矿作业产生的温室气体排放量，该作业将水返回到月球轨道内的任何地方，即所谓的顺月轨道。他们将这项排放量与将同样体积的水从地球送入轨道的排放量进行了比较。
The big difference is that a water-carrying vehicle from Earth can haul only a small percentage of its mass as water. But an asteroid-mining spacecraft can transport a significant multiple of its mass as water to cis-lunar orbit. “Substantial savings in greenhouse gas emissions can be achieved,” say Hein and co.
最大的区别是，地球上运水的车辆只能运送其车辆质量的一小部分作为水。但是，一艘小行星采矿的航天器可以将其质量的很大一部分作为水输送到顺月轨道。海因及其同事表示:“这可以实现温室气体的大幅减排。”
This interesting work should help to focus minds on the environmental impacts of mining, which are rapidly increasing in profile. But it is only a first step. There is significant uncertainty in the numbers here, so these will need to be better understood.
这项有趣的工作应有助于使人们将注意力集中在采矿对环境的影响上，而这种影响从正在从侧面迅速增加。但这只是第一步。这些数字有很大的不确定性，所以这些需要被更好地理解。
Other factors will also eventually need to be taken into account. The Earth-bound mining industry could become more environmentally friendly by using renewable energy rather than burning coal to generate power (as it does in South Africa). Rocket launching could also become greener if more eco-friendly fuels are developed. Both these things would change the numbers.
最后还需要考虑其他因素。通过使用可再生能源而不是烧煤发电(就像南非那样)，地球上的采矿业将变得更环保。如果开发出更环保的燃料，火箭发射也会变得更加绿色环保。这两种情况都会改变这些数字。
There are also emissions that this analysis does not take into account. For example, it does not include the emissions from mission control on Earth or from launch-pad construction. Then there are the ongoing effects of rocket launches on the ozone layer, which also need to be considered.
这种分析也没有考虑到排放问题。例如，它不包括来自地面任务控制或发射台建设的排放。此外，还需要考虑火箭发射对臭氧层的持续影响。
So there is more work to be done. But Hein and co have taken a significant first step toward realistic environmental life-cycle assessments for asteroid mining, a task that will surely become more pressing as this industry matures.
所以还有更多的工作要做。但是海因和他的同事已经向小行星采矿的现实环境生命周期评估迈出了重要的第一步，随着这个行业的成熟，这个任务一定会变得更加紧迫。
Ref: arxiv.org/abs/1810.04749 : Exploring Potential Environmental Benefits of Asteroid Mining
引用:arxiv.org/abs/1810.04749:探索行星探矿潜在的环境效益
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