趕往火星？宇宙射線不好惹！

by Adam Cole

NASA worker： T-minus[倒計(jì)時(shí)用語(yǔ)] ten， nine， eight...

In November of 2011， the Mars Science Laboratory lifted off[發(fā)射]， carrying Curiosity， NASAs Mars rover[飛行器]， into space.

NASA worker： ...one， main engine start， zero and lift off of Curiosity.

And then in August... Allen Chen （NASA engineer）： Touchdown confirmed[確認(rèn)]. Were safe on Mars.

During the eight months in between， Curiosity was bombarded[轟擊] with lots of radiation[輻射]， high-energy protons[質(zhì)子] thrown out by the sun and

galactic[銀河的] cosmic rays[宇宙射線] slicing[像刀一樣運(yùn)動(dòng)]

through the solar system from distant supernovas[超新星]. Here on Earth， the magnetic field and atmosphere[大氣] shield[防護(hù)] us from most of this radiation. But out in the void[空間] of space， high-energy particles[粒子] would rip[撕破，割裂] into an astronauts DNA， slowly increasing the risk of cancer. Thats a problem for NASA and the handful of other private companies who have pledged[保證] to send humans to Mars.

For a long time， theyve tried to figure out just how much radiation an astronaut would experience on the journey. Enter Curiosity， handily[方便地] equipped with RAD， the Radiation Assessment[評(píng)估] Detector[探測(cè)器]. It was designed to gather radiation data on the surface of Mars.

Don Hassler of the Southwest Research Institute leads the RAD team.

Don Hassler： About two years before launch， we started to realize the fact that RAD was tucked[擠進(jìn)] inside the belly of the spacecraft sort of in the same location that a future astronaut might be.

So they thought： Why not turn it on during space flight？ A few days after launch， RAD powered up and started collecting data. In the journal Science， the researchers announced that the bulk[大量] of the radiation—95 percent—was caused by galactic cosmic rays that we dont know how to shield against. Hassler says theres really only one way to minimize the damage caused by these rays.

Hassler： I think we just want to go quickly.

The shortest possible trip to Mars with current technology would take about six months. During that time， Hassler says an astronaut would experience about four times more radiation than people on the International Space Station， who would be partially[部分地] shielded by their proximity[接近] to Earth.

Hassler： An astronaut on ISS for， say， six months， you know， would receive on the order of maybe 80 millisieverts[（單位）毫西弗]， compared with the 330 that we receive on our way to Mars.

The average American is only exposed to six millisieverts every year. Three hundred and thirty millisieverts is enough to increase your cancer risk by about one and a half percent or so. Double that number for a round trip visit to Mars， and you quickly approach[接近] the limits recommended[推薦] by the National Council on Radiation Protection. But that doesnt discourage Robert Zubrin.

Robert Zubrin： Radiation is not a showstopper[干擾物].

Zubrin is the president of The Mars Society and author of The Case for Mars.

Zubrin： Its not something that the FDA注would recommend that everyone do， but， you know， were talking about a mission to Mars here.

Zubrin says there are plenty of other risks involved in a Mars mission， like can they even land， and those are risks that many would be willing to take. The average person already has about a 20 percent chance of dying from cancer. A 40-year-old astronaut， who dreams of setting foot on the red planet， might not care about bumping that number up[提高] a few percentage points. Zubrin： Theres no cause for delay， at least as far as radiation is concerned， and we should now set our course for Mars.

Scientists still have questions about radiation on Mars itself. They need more data to better understand the cancer risk for Mars settlers on the surface. But dont worry， Curiosity is working on that too.

美國(guó)國(guó)家航空航天局員工：倒計(jì)時(shí)，十、九、八……

火星科學(xué)實(shí)驗(yàn)室于2011年11月升空，將美國(guó)國(guó)家航空航天局（NASA）的火星車“好奇號(hào)”送入太空。

美國(guó)國(guó)家航空航天局員工：……一，主引擎啟動(dòng)；零，好奇號(hào)升空。

然后到了（2012年）8月……

陳友倫（美國(guó)國(guó)家航空航天局工程師）：確認(rèn)著陸。我們安全抵達(dá)火星。

在這之間的八個(gè)月當(dāng)中，大量輻射、太陽(yáng)發(fā)出的高能量質(zhì)子以及遠(yuǎn)方的超新星穿越整個(gè)太陽(yáng)系投射過(guò)來(lái)的銀河宇宙射線對(duì)好奇號(hào)進(jìn)行了輪番轟炸。在地球上，這類輻射大多被磁場(chǎng)與大氣層擋在外頭。而在太空空間當(dāng)中，高能量粒子會(huì)侵入宇航員的DNA，逐步增加人體患癌機(jī)率。這正是美國(guó)國(guó)家航空航天局以及其他幾家承諾送人上火星的私人企業(yè)所面臨的問(wèn)題。

很長(zhǎng)一段時(shí)間以來(lái)，他們一直試圖搞清楚宇航員會(huì)在太空旅程中經(jīng)受多少輻射。好奇號(hào)登場(chǎng)了，其內(nèi)部極其便捷地裝備了輻射評(píng)估探測(cè)器（RAD）。該儀器用于收集火星表面的輻射數(shù)據(jù)。

美國(guó)西南研究院的唐·哈斯勒是這項(xiàng)探測(cè)的領(lǐng)隊(duì)。唐·哈斯勒：早在（好奇號(hào)）發(fā)射的兩年前，我們就意識(shí)到這個(gè)探測(cè)器會(huì)被安裝在航天器內(nèi)部，這個(gè)位置正好就是將來(lái)宇航員坐的地方。

于是他們想到：為什么不在太空飛行時(shí)就打開(kāi)儀器呢？發(fā)射過(guò)后幾天，探測(cè)器通上電，開(kāi)始收集數(shù)據(jù)。研究人員在《科學(xué)》雜志上宣稱大部分輻射——高達(dá)95%的輻射來(lái)自銀河宇宙射線，而我們根本不知道如何阻隔這類射線。哈斯勒說(shuō)，只有一種辦法可以將這類射線的危害降至最低。

哈斯勒：我想我們只能快點(diǎn)去那里。

以目前的技術(shù)水平，前往火星的旅程最短也要六個(gè)月。哈斯勒說(shuō)，宇航員在此期間所受到的輻射量是國(guó)際空間站（輻射量）的四倍——后者由于臨近地球，輻射受到一定程度的阻隔。

哈斯勒：比如說(shuō)一個(gè)宇航員在空間站呆上六個(gè)月，你知道，他所受的（輻射量）大概是80毫西弗，而我們?cè)诨鹦侵卯?dāng)中會(huì)受到330毫西弗的輻射。

而普通的美國(guó)人每年所受的輻射量?jī)H為6毫西弗。330毫西弗足以讓致癌機(jī)率上升將近1.5%。如果從火星往返，這個(gè)數(shù)字還要乘以二，馬上就接近美國(guó)輻射保護(hù)委員會(huì)所建議的輻射上限了。但羅伯特·祖布林并未因此而喪氣。

羅伯特·祖布林：輻射并不是攔路虎。

祖布林是火星學(xué)會(huì)主席以及《趕往火星：紅色星球定居計(jì)劃》的作者。

祖布林：這并不是什么美國(guó)食品和藥物管理局（FDA）建議所有人都要去做的事情，你知道，我們現(xiàn)在討論的可是前往火星的任務(wù)呢。

祖布林說(shuō)，火星任務(wù)還有很多其他危險(xiǎn)，比如“他們真能登陸火星嗎”——但很多人愿意承受這樣的風(fēng)險(xiǎn)。普通人也有將近20%的癌癥死亡率，而一名渴望踏足紅色星球的40歲宇航員也許并不在乎給這個(gè)概率增加幾個(gè)百分點(diǎn)。

祖布林：（火星任務(wù)）沒(méi)有延遲的理由，至少就輻射而言不成理由，我們現(xiàn)在就應(yīng)該開(kāi)始向火星進(jìn)軍。

科學(xué)家對(duì)火星本身的輻射問(wèn)題依然存疑。他們需要更多數(shù)據(jù)，才能更好地確定火星定居者們的患癌危險(xiǎn)性。不過(guò)你無(wú)需擔(dān)心，好奇號(hào)正為此忙乎著呢。