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我们会征服火星吗?

2015年06月10日08:40    来源:中国科技网    手机看新闻
原标题:我们会征服火星吗?

  中国科技网6月8日报道(张微 编译)火星。这里是一个不毛之地。在这个干旱,甚至可以说干燥的世界里,地表温度是-55 °C (-67 °F)。而在它的两极,温度可低至-153 °C (243 °F)。这在很大程度上与火星稀薄的大气层有关,因为火星的大气层过于稀薄难以保存热量(更别提呼吸了)。但为什么征服火星的想法对我们有如此大的吸引力呢?

  这其中包含很多原因,包括我们两颗行星之间的相似性,可利用的水,有产生食物和氧气的可能,以及可以就地取材的建筑材料。甚至有利用火星作为原材料来源并将其改造成一个宜居环境的长远计划。让我们来逐一分析。

  优势:

  正如前文提到的,地球与火星之间具有很多相似之处,使得人类定居火星成为一个可行的选择。首先,火星和地球上一天的长度非常接近。火星上一天是24小时39分钟,这意味着对动植物,以及人类来说定居在这里会很适应。

  火星和地球一样自转轴也是倾斜的,这意味着它与地球具有相同的季节模式(尽管时间较长)。基本上,当一个半球朝向太阳的时候,这个半球就是夏天,另一个半球正在经历寒冬——结束了其温暖而漫长的日子。

  进入到万物生长的季节也是工作的好时候,为定居火星的人们提供一种熟悉的安全感以及测量一年的方式。这与地球上的农民类似,火星人将经历一个“种植季”,一个“收获季”,并将举行一年一度的庆祝活动,标志着季节的变化。

  同时,与地球一样,火星位于太阳系的可居住区内(又名适居带),虽然它的轨道处于太阳系宜居带的外侧。金星同样位于这个区域内,但其位置靠内侧(有一层厚厚的大气层),使它成为太阳系中最热的星球。并且由于金星整日下着硫酸雨,使得火星对我们更具吸引力。

  此外,火星是除了金星之外,太阳系中最接近地球的行星,我们已经考虑了难道火星不是一个好的选项嘛!实际上,每隔几年,当地球和火星在冲日时——它们彼此距离接近,距离在变化时,就是将移民送上火星的理想“发射窗口”期。

  例如,2014年4月8日,地球和火星相距9240万公里(5740万英里)。在2016年5月22日,它们之间的距离将达到7530万公里(4680万英里),2018年7月27日,仅距离5760万公里(3580万英里)。在这些窗口期,去火星将花费几个月,而不是耗时几年。

  另外,火星上有大量以冰的形态存在的水。大部分的这类水冰位于极地地区,但是火星陨石的调查表明,大量的水冰被锁定在地表之下。这些水能够很轻松地加以提存和净化从而供人类使用。

  在他的书中《The Case for Mars》,罗伯特 祖布林是描述了未来人类移民如何在那片土地上生活,并最终定居下来。与国际空间站上的宇航员不同,定居火星不需要把所有物资都从地球上带过去,未来的火星移民能够自己制造空气,水,甚至可以将火星水分裂成氢气和氧气来获取燃料。

  初步实验表明,火星土壤可以被烤成砖块来建造防护结构,从而减少了被运送到火星表面的必备材料。地球上的植物如果能够得到足够的阳光和二氧化碳,那么它们也能在火星土壤上生长。随着时间的推移,在火星土壤上种植植物还能够提供可供呼吸的空气。

  挑战:

  尽管有上述好处,但移居到这个红色星球也是一个伟大的挑战。首先,就是地表的平均温度问题,这种酷寒绝不是一个好客的温度。中午,赤道周围的温度能够达到温和的20 °C,好奇号的地点,盖尔陨石坑,这里接近赤道,夜间温度低至-70 °C。

  火星重力只有地球的40%,我们很难适应这一点。根据NASA的报告,失重对人体的影响相当大,能够在一周时间里,损失高达5%的肌肉质量,在一个月时间里,损失1%的骨密度。

  当然,在火星表面这些损失没有那么多,至少那里还有一些重力。但从长期来看,永久定居火星的人不得不面对肌肉坏死和骨质疏松的问题。

  然后就是那里的大气,火星大气让人无法呼吸。这个星球大气层中95%都是二氧化碳,定居者不但要生产可供呼吸的空气,而且离不开压力服和氧气瓶。

  火星没有像地球上的全球性的磁场。而且由于其稀薄的大气层,这意味着大量的电离辐射能够到达火星表面。

  由于火星奥德赛飞船的火星辐射环境试验的测量,科学家们发现火星轨道上的辐射水平比国际空间站高2.5倍。尽管火星表面的辐射会低一点,但人类仍然会不适应。

  麻省理工学院一个研究团队提交的论文中,分析了2020年开始的移民火星计划,他们得出的结论是,第一位宇航员将在68天后窒息而死,其他的人会死于饥饿、脱水,或在富氧大气中燃烧。

  简而言之,在火星上建立永久定居点的挑战很多,但不一定是不可逾越的。

  地球化:

  随着时间的流逝,定居火星的许多或所有的困难都可以通过地球工程的应用得到克服。利用蓝藻细菌和浮游植物等生物,定居者可以逐渐把大气中的二氧化碳转换成可呼吸的氧气。

  此外,据估计,在火星南极有大量二氧化碳以干冰的形态存在,还有的被火星的风化层(土壤)吸收。如果火星温度升高,这些冰将升华成气体,增加大气压力。虽然这对人类来说仍然无法呼吸,但也足够消除人类对压力服的依赖。

  要想达到这一目的,有一个可行的方式就是引发这个星球上的温室效应。可以从太阳系其它行星的大气层中引入氨冰来实现。因为氨(NH3)是氮和氢的化合物,其主要重量是氮,氮可以提供呼吸所需的缓冲气体,就像在地球上一样。

  同样,也可以引入碳氢化合物如甲烷——泰坦的大气和地表中很常见,来触发温室效应。甲烷可以被释放到大气中,起到加重温室效应的作用。

  美国宇航局艾姆斯研究中心的天体生物学家,祖布林和克里斯麦凯也建议,在火星表面建造可以向大气中释放温室气体的设施,从而引发全球变暖(就像它们在地球上一样)。

  其它的可能性也存在,从能够加热地表的轨道镜面到利用彗星撞击地表。但无论采用哪种方法,改造火星环境的可能性是存在的,从长远来看,这些方法能够让火星更适合人类居住,其中许多方法我们也正在地球上做出尝试(虽然还没有产生积极的结果)。

  另一个解决方案是,建设地下定居点。通过建造一系列的隧道连接各个地下定居点,当定居者离开家的时候,可以摆脱氧气瓶和压力服的束缚。

  此外,这种方法还能够防辐射。根据火星勘测轨道飞行器获得的数据,可以推测出,生活在地下环境中是一个更有吸引力的选择。

  提出的任务:

  美国宇航局提出的载人火星任务——将在21世纪30年代开始,使用“猎户座”多用途载人飞船(MPCV)和太空发射系统(SLS)——这并不是唯一一个把人类送到红色星球的提议。除了其它联邦太空机构外,还有许多私人企业和非营利组织也有这项计划,其中的一些计划更加野心勃勃而不仅仅是探索。

  欧洲航天局(ESA)也有一个派遣人类去火星的长期计划,尽管他们还没有建设一个载人飞船。随着俄罗斯早在2011年就已经完成了火星模拟(称为火星500),俄罗斯联邦宇航局也正在计划载人火星任务,欧洲宇航局目前也正在参与火星模拟。

  2012年,荷兰企业家透露在2030年开始在火星建立人类聚居地计划,被称为火星一号,这项计划将招募一批有去无回的志愿者永久定居火星,并将通过媒体的参与进行筹资。

  “火星一号”计划的其它细节包括,在2018年发射电信卫星,2020年发射火星车,2023年将基地部件和志愿者送到火星上。这个基地由3000平方米的太阳能电池板供给能源,并且猎鹰9号重型火箭将用来发射硬件。首批四名宇航员将在2025年登陆火星;然后每两年将有新的四名宇航员到达。

  2014年12月2日,美国航空航天局的高级人类探索系统和操作任务主任杰森 库鲁森和该计划的副局长杰姆斯 鲁瑟宣布,支持波音公司“负担得起的火星任务设计”。目前计划在21世纪30年代,发射任务包括辐射屏蔽计划,离心式人工重力,运输消耗补给,和返回着陆。

  SpaceX公司和特斯拉首席执行官Elon Musk还宣布建立一个80000人的火星定居计划。这一计划的本质是火星定居飞船(MCT)的发展,一个航天系统,利用可重复使用的火箭发动机,运载火箭和太空舱运送人类登陆火星并返回地球。

  截至2014年,SpaceX公司已经开始为火星定居飞船开发大型猛禽火箭发动机,但MCT预计到21实际20年代中期才会投入使用,Musk说,他希望在2015年底,为火星运输系统发布“全新建筑”的细节。

  也许会有那么一天,经过几代火星移民的改造,火星也能够具有经济价值。可能发现某种形式的矿藏,然后运回地球用于出售。由于火星表面重力小,将一些重金属如铂运回地球的成本较低。

  根据Musk的说法,最可能的情况是(至少在可预见的未来)房地产经济的发展。由于地球上的人口爆炸式增长,一个提供足够空间的新的定居点是一项很好的投资。一旦交通问题得到解决,精明的投资者就会开始购买土地。

  总之,如果有一天,出现了真正的火星人,那一定是我们!

  英文原文:

  Will we ever colonize Mars?

  Mars. It's a pretty unforgiving place. On this dry, dessicated world, the average surface temperature is -55 °C (-67 °F). And at the poles, temperatures can reach as low as -153 °C (243 °F). Much of that has to do with its thin atmosphere, which is too thin to retain heat (not to mention breathe). So why then is the idea of colonizing Mars so intriguing to us?

  Well, there are a number of reasons, which include the similarities between our two planets, the availability of water, the prospects for generating food, oxygen, and building materials on-site. And there's even the long-term benefits of using Mars as a source of raw materials and terraforming it into a liveable environment. Let's go over them one by one…

  Benefits:

  As already mentioned, there are many interesting similarities between Earth and Mars that make it a viable option for colonization. For starters, Mars and Earth have very similar lengths of days. A Martian day is 24 hours and 39 minutes, which means that plants and animals – not to mention human colonists – would find that familiar.

  Mars also has an axial tilt that is very similar to Earth's, which means it has the same basic seasonal patterns as our planet (albeit for longer periods of time). Basically, when one hemisphere is pointed towards the Sun, it experiences summer while the other experiences winter – complete with warmer temperatures and longer days.

  This too would work well when it comes to growing seasons and would provide colonists with a comforting sense of familiarity and a way of measuring out the year. Much like farmers here on Earth, native Martians would experience a "growing season", a "harvest", and would be able to hold annual festivities to mark the changing of the seasons.

  Also, much like Earth, Mars exists within our Sun's habitable zone (aka. "goldilocks zone"), though it is slightly towards its outer edge. Venus is similarly located within this zone, but its location on the inner edge (combined with its thick atmosphere) has led to it becoming the hottest planet in the Solar System. That, combined with its sulfuric acid rains makes Mars a much more attractive option.

  Additionally, Mars is closer to Earth than the other Solar planets – except for Venus, but we already covered why it's not a very good option! This would make the process of colonizing it easier. In fact, every few years when the Earth and Mars are at opposition – i.e. when they are closest to each other – the distance varies, making certain "launch windows" ideal for sending colonists.

  For example, on April 8th, 2014, Earth and Mars were 92.4 million km (57.4 million miles) apart at opposition. On May 22nd, 2016, they will be 75.3 million km (46.8 million miles) apart, and by July 27th of 2018, a meager 57.6 million km (35.8 million miles) will separate our two worlds. During these windows, getting to Mars would be a matter of months rather than years.

  Also, Mars has vast reserves of water in the form of ice. Most of this water ice is located in the polar regions, but surveys of Martian meteorites have suggested that much of it may also be locked away beneath the surface. This water could be extracted and purified for human consumption easily enough.

  In his book, The Case for Mars, Robert Zubrin also explains how future human colonists might be able to live off the land when traveling to Mars, and eventually colonize it. Instead of bringing all their supplies from Earth – like the inhabitants of the International Space Station – future colonists would be able to make their own air, water, and even fuel by splitting Martian water into oxygen and hydrogen.

  Preliminary experiments have shown that Mars soil could be baked into bricks to create protective structures, which would cut down on the amount of materials needed to be shipped to the surface. Earth plants could eventually be grown in Martian soil too, assuming they get enough sunlight and carbon dioxide. Over time, planting on the native soil could also help to create a breathable atmosphere.

  Challenges:

  Despite the aforementioned benefits, there are also some rather monumental challenges to colonizing the Red Planet. For starters, there is the matter of the average surface temperature, which is anything but hospitable. While temperatures around the equator at midday can reach a balmy 20 °C, at the Curiosity site – the Gale Crater, which is close to the equator – typical nighttime temperatures are as low as -70 °C.

  The gravity on Mars is also only about 40% of what we experience on Earth's, which would make adjusting to it quite difficult. According to a NASA report, the effects of zero-gravity on the human body are quite profound, with a loss of up to 5% muscle mass a week and 1% of bone density a month.

  Naturally, these losses would be lower on the surface of Mars, where there is at least some gravity. But permanent settlers would still have to contend with the problems of muscle degeneration and osteoporosis in the long run.

  And then there's the atmosphere, which is unbreathable. About 95% of the planet's atmosphere is carbon dioxide, which means that in addition to producing breathable air for their habitats, settlers would also not be able to go outside without a pressure suit and bottled oxygen.

  Mars also has no global magnetic field comparable to Earth's geomagnetic field. Combined with a thin atmosphere, this means that a significant amount of ionizing radiation is able to reach the Martian surface.

  Thanks to measurements taken by the Mars Odyssey spacecraft's Mars Radiation Environment Experiment (MARIE), scientists learned that radiation levels in orbit above Mars are 2.5 times higher than at the International Space Station. Levels on the surface would be lower, but would still be higher than human beings are accustomed to.

  In fact, a recent paper submitted by a group of MIT researchers – which analyzed the Mars One plan to colonize the planet beginning in 2020 – concluded that the first astronaut would suffocate after 68 days, while the others would die from a combination of starvation, dehydration, or incineration in an oxygen-rich atmosphere.

  In short, the challenges to creating a permanent settlement on Mars are numerous, but not necessarily insurmountable.

  Terraforming:

  Over time, many or all of the difficulties in living on Mars could be overcome through the application of geoengineering (aka. terraforming). Using organisms like cyanobacteria and phytoplankton, colonists could gradually convert much of the CO2 in the atmosphere into breathable oxygen.

  In addition, it is estimated that there is a significant amount of carbon dioxide (CO2) in the form of dry ice at the Martian south pole, not to mention absorbed by in the planet's regolith (soil). If the temperature of the planet were raised, this ice would sublimate into gas and increase atmospheric pressure. Although it would still not be breathable by humans, it would be sufficient enough to eliminate the need for pressure suits.

  A possible way of doing this is by deliberately triggering a greenhouse effect on the planet. This could be done by importing ammonia ice from the atmospheres of other planets in our Solar System. Because ammonia (NH3) is mostly nitrogen by weight, it could also supply the buffer gas needed for a breathable atmosphere – much as it does here on Earth.

  Similarly, it would be possible to trigger a greenhouse effect by importing hydrocarbons like methane – which is common in Titan's atmosphere and on its surface. This methane could be vented into the atmosphere where it would act to compound the greenhouse effect.

  Zubrin and Chris McKay, an astrobiologist with NASA's Ames Research center, have also suggested creating facilities on the surface that could pump greenhouse gases into the atmosphere, thus triggering global warming (much as they do here on Earth).

  Other possibilities exist as well, ranging from orbital mirrors that would heat the surface to deliberately impacting the surface with comets. But regardless of the method, possibilities exist for transforming Mars' environment that could make it more suitable for humans in the long run – many of which we are currently doing right here on Earth (with less positive results).

  Another proposed solution is building habitats underground. By building a series of tunnels that connect between subterranean habitats, settlers could forgo the need for oxygen tanks and pressure suits when they are away from home.

  Additionally, it would provide protection against radiation exposure. Based on data obtained by the Mars Reconnaissance Orbiter, it is also speculated that habitable environments exist underground, making it an even more attractive option.

  Proposed Missions:

  NASA's proposed manned mission to Mars – which is slated to take place during the 2030s using the Orion Multi-Purpose Crew Vehicle (MPCV) and the Space Launch System (SLS) – is not the only proposal to send humans to the Red Planet. In addition to other federal space agencies, there are also plans by private corporations and non-profits, some of which are far more ambitious than mere exploration.

  The European Space Agency (ESA) has long-term plans to send humans, though they have yet to build a manned spacecraft. Roscosmos, the Russian Federal Space Agency, is also planning a manned Mars mission, with simulations (called Mars-500) having been completed in Russia back in 2011. The ESA is currently participating in these simulations as well.

  In 2012, a group of Dutch entrepreneurs revealed plans for a crowdfunded campaign to establish a human Mars base, beginning in 2023. Known as MarsOne, the plan calls for a series of one-way missions to establish a permanent and expanding colony on Mars, which would be financed with the help of media participation.

  Other details of the MarsOne plan include sending a telecom orbiter by 2018, a rover in 2020, and the base components and its settlers by 2023. The base would be powered by 3,000 square meters of solar panels and the SpaceX Falcon 9 Heavy rocket would be used to launch the hardware. The first crew of 4 astronauts would land on Mars in 2025; then, every two years, a new crew of 4 astronauts would arrive.

  On December 2nd, 2014, NASA's Advanced Human Exploration Systems and Operations Mission Director Jason Crusan and Deputy Associate Administrator for Programs James Reuthner announced tentative support for the Boeing "Affordable Mars Mission Design". Currently planned for the 2030s, the mission profile includes plans for radiation shielding, centrifugal artificial gravity, in-transit consumable resupply, and a return-lander.

  SpaceX and Tesla CEO Elon Musk has also announced plans to establish a colony on Mars with a population of 80,000 people. Intrinsic to this plan is the development of the Mars Colonial Transporter (MCT), a spaceflight system that would rely of reusable rocket engines, launch vehicles and space capsules to transport humans to Mars and return to Earth.

  As of 2014, SpaceX has begun development of the large Raptor rocket engine for the Mars Colonial Transporter, but the MCT is not expected to be operational until the mid-2020s. In January 2015, Musk said that he hoped to release details of the "completely new architecture" for the Mars transport system in late 2015.

  There may come a day when, after generations of terraforming and numerous waves of colonists, that Mars will begin to have a viable economy as well. This could take the form of mineral deposits being discovered and then sent back to Earth for sale. Launching precious metals, like platinum, off the surface of Mars would be relatively inexpensive thanks to its lower gravity.

  But according to Musk, the most likely scenario (at least for the foreseeable future) would involve an economy based on real estate. With human populations exploding all over Earth, a new destination that offers plenty of room to expand is going to look like a good investment. And once transportation issues are worked out, savvy investors are likely to start buying up land.

  In short, one day, there could be real Martians – and they would be us!

(责编:赵竹青、马丽)


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