火星“地球化”需要做什么？| Nature Podcast

又到了每周一次的 Nature Podcast 时间了！欢迎收听本周由Ellie Mackay和Adam Levy带来的一周科学故事，本期播客片段讨论改造火星大气。欢迎前往iTunes或你喜欢的其他播客..下载完整版，随时随地收听一周科研新鲜事。 [原文来自：www.11jj.com]

音频文本：

Interviewer: Ellie Mackay

First up this week: have you ever thought about living on Mars? Right now, it’s not the most inviting environment. But there have been plenty of ideas about how that might be changed. Here’s Bruce Jakosky – he’s one of the authors of a paper in Nature Astronomy this week, and he’s been looking at how realistic some of these ideas might be.

Interviewee: Bruce Jakosky

Right now, the average temperature at the surface of Mars is about -60°C, and if we could raise it up to 0 °C, then we could have liquid water. That would allow us to function as humans in the environment without the need for domes or habitats.

Interviewer: Ellie Mackay

Bruce is talking about the concept of terraforming Mars – modifying the atmosphere to make the planet more Earth-like, and therefore habitable. But it’s not just the temperature that’s an issue. For us to live there, the atmospheric pressure of Mars would need to be 150 times greater than it is today. Yet proposals to terraform Mars have become increasingly popular. Iasked Bruce how realistic the concept of terraforming Mars actually is.

Interviewee: Bruce Jakosky

What you can’t see is that I’m smiling at that question, because the less we know about how we would actually terraform Mars, the easier we think it is, and as you begin to explore it, it gets harder and harder. Right now, it’s in the realm of science fiction because we don’t really know how to do it, and I think the fact that we’re changing the environment on the Earth inadvertently underscores the fact that we really don’t understand how climates work. Despite that, a lot of people have been speculating in the press lately about how easy it might be to terraform Mars. Our paper will be an interesting contrast to that, in terms of dashing some people’s hopes, to be honest.

Interviewer: Ellie Mackay

Well that doesn’t sound very encouraging, but to start off with, can you explain what’s actually being proposed? So, from a scientific point of view, how might we overcome these barriers of temperature and pressure?

Interviewee: Bruce Jakosky

If we wanted to terraform Mars, the way we would do it would be to put a greenhouse gas in the atmosphere. That would serve both functions of increasing the pressure and by trapping heat from the sun, increasing the temperature. And that really depends on the availability of greenhouse gases or our ability to manufacture them. The most available and accessible greenhouse gas at Marswould be carbon dioxide – CO2.

Interviewer: Ellie Mackay

Okay, and so this is what your research was looking at?

Interviewee: Bruce Jakosky

So, we wanted to look at the inventory of CO2 on the planet – where reservoirs of CO2, if you will, reside, how much would be there, and how easy it would be to mobilise it and put it back into the atmosphere.

Interviewer: Ellie Mackay

Essentially, that’s what we’re doing to this planet with global warming and we’re trying to force a way to do that somewhere else. So it’s like we could send all of our industry and all of our fossil fuel burning over to Mars, and it would have a beneficial effect over there, instead of…

Interviewee: Bruce Jakosky

That’s absolutely right. We don’t even need to send the manufacturing and industry to Mars, we could just ship all the CO2 there. And that would solve both planets’ problems. It’s totally facetious and absolutely unworkable. We don’t have that much CO2 in our atmosphere, and the number of rockets you would have to ship to get the CO2 there is immense.

Interviewer: Ellie Mackay

Okay, so if we can’t ship it there, let’s get back to this idea of using reserves of CO2 on Mars. Your paper mentions several possible sinks –there’s CO2 in the polar ice, there’s some in minerals called carbonates, and there’s gas that gets bound to the layer of soil called the regolith on the surface of the planet. So, that seems like a lot of different places for the CO2 to be trapped. How might we mobilise or release it from these sources?

Interviewee: Bruce Jakosky

Probably the easiest is the CO2 locked up in the polar ice. All you need to do is spread dark dust over the polar caps, and it would absorb more sunlight and heat up. That’s the easiest one, and if that sounds hard, you may not like the next ones. The carbonates you have to heat up to temperatures at which they break apart, and that’s around 300 °C. That automatically means a large scale industrial operation, and it wouldn’t get you very much. I think the most difficult CO2 to mobilise is gas that is physically attached to the soil. You would almost have to strip-mine the entire planet in order to put that gas back into the atmosphere, and that won’t work because once you put it there it’ll go right back into the regolith.So this question of how easy it is to get it out of these sinks and into the atmosphere is a really important one. Ultimately, it’s not possible.

Interviewer: Ellie Mackay

If it were to become possible to do somehow, melting the polar ice caps seems to be the most popular solution. How much CO2 is actually trapped there?

Interviewee: Bruce Jakosky

At one time we thought there might have been the equivalent of an Earth’s atmosphere of gas in the polar caps, but that idea is demonstrably wrong based on our knowledge today. The estimates today are that if you put all the CO2 in the polar caps into the atmosphere it would only double the atmospheric pressure.

Interviewer: Ellie Mackay

So that’s not even close?

Interviewee: Bruce Jakosky

No, so that’s a very small increment. This amount of CO2 just isn’t enough to even have a start at raising the temperature or the pressure.

Interviewer: Ellie Mackay

And what about if we added the CO2 from the other sources, the rocks and the minerals, the soil, and released all of the CO2 from all these different reserves?

Interviewee: Bruce Jakosky

We’ve looked at how much CO2 can be locked up in each of these sinks for CO2 that are remaining on the planet. If we could mobilise all of it and put it back into the atmosphere, we would still have less than 10% of the amount of CO2 we need to raise the temperature. So, the most we can get is a tiny fraction of what would be needed.

Interviewer: Ellie Mackay

Is that what you expected to find?

Interviewee: Bruce Jakosky

It’s the answer we knew going in. I think within the Mars community this is not a surprising answer. I’ll be honest, that’s why we wrote this paper, because people are getting up and talking about how easy it is to terraform the planet, without having a realistic understanding of what would be involved and where the CO2 is and how much there is.

Interviewer: Ellie Mackay

So, does this mean this is the end of the concept of terraforming Mars?

Interviewee: Bruce Jakosky

This doesn’t mean we can’t terraform the planet. It means we can’t do it today with available technology. People have also talked about manufacturing molecules that are very effective greenhouse gases, things like Freon, but the scale of manufacturing that would be required to produce enough is so far beyond our current capability that you have to put it into the distant future.

Interviewer: Ellie Mackay

So what would you say to those people who are keen to inhabit Mars in the relatively near future?

Interviewee: Bruce Jakosky

Well first of all, I don’t think this impacts either our desire or our ability to explore Mars with humans. We can carry out that kind of a mission beginning today, and it would be exciting from the human perspective and from the science perspective. And this is part of that process of discussing what’s possible and where we as a society want to head. I think if we’re going to talk about sending humans to Mars, we need to do it in the context of a real and valid understanding of what is on the planet, based on the best available scientific information today.

Interviewer: Ellie Mackay

That was Bruce Jakosky from the University of Colorado in the US. To read that story in Nature Astronomy, you can head over to nature.com/natastron.ⓝ

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