正文翻譯

Mars once had water flowing over the surface, but it disappeared billions of years ago. A new study suggests that in addition to being lost to space, much of the water could have been trapped in minerals in the planet's crust.

火星表面曾經(jīng)有過(guò)水，但數(shù)十億年前就消失了。一項(xiàng)新的研究表明，除了消失在太空之外，大部分水可能被困在這個(gè)星球地殼的礦物質(zhì)中。

Oceans’ worth of ancient water may have been locked up in minerals in Mars's crust, increasing estimates for the total amount of that once flowed on the red planet.

具有海洋價(jià)值的古代水可能被鎖在火星地殼的礦物質(zhì)中，這使得研究人員對(duì)曾經(jīng)在這顆紅色星球上流動(dòng)的水總量的估計(jì)增加了。

BY ROBIN GEORGE ANDREWS

作者羅賓·喬治·安德魯斯

Today, Mars is a frigid desert. But dried up deltas and riverbanks reveal that water once flowed over the plant’s surface. Where did it all go? Scientists have been trying to answer this question for decades, hoping to understand how Mars became an arid wasteland while its neighbor, Earth, kept hold of its water and became a biological paradise.

目前，火星是一個(gè)寒冷的沙漠。但這個(gè)星球上干涸的三角洲和河岸表明這個(gè)星球表面曾有水的痕跡。但是水都到哪里去了呢? 幾十年來(lái)，科學(xué)家們一直試圖回答這個(gè)問題，希望了解在其鄰居地球能保持水源，成為生物天堂的情況下，火星是如何變成貧瘠的荒地的。

Now, by plugging observations of the red planet into new models, a team of geologists and atmospheric scientists has come up with a new picture of Mars’s past: Much of the planet’s ancient water could have been trapped within minerals in the crust, where it remains to this day.

最近，一個(gè)由地質(zhì)學(xué)家和大氣科學(xué)家組成的團(tuán)隊(duì)通過(guò)將對(duì)紅色星球的觀測(cè)數(shù)據(jù)插入到新的模型中的方法，計(jì)算得出了火星過(guò)去的新圖像: 地球上許多古老的水可能被封存在地殼的礦物質(zhì)中，而且這些水直到今天仍存在那里。

Prior research suggested that most of Mars’s water escaped into space as its atmosphere was stripped away by the sun’s radiation. But this new study, published today in the journal Science and virtually presented at this year’s Lunar and Planetary Science Conference, concludes that Mars’s water experienced both an atmospheric exodus and a geologic entrapment.

先前的研究表明，由于火星的大氣層被太陽(yáng)輻射剝離，火星上的大部分水都逃到了太空中。但最近發(fā)表在《科學(xué)》(Science)雜志上的這項(xiàng)新研究得出結(jié)論稱，火星上的水實(shí)際上經(jīng)歷了大氣流失和地質(zhì)圈藏兩種方式。這項(xiàng)研究還在今年的月球和行星科學(xué)會(huì)議上進(jìn)行了虛擬展示。

Depending on how much water you start with, the new model estimates that anywhere beTween 30 and 99 percent of it was incorporated into minerals in the planet’s crust, while the remaining fraction escaped into space. It’s a big range, and both processes likely played a role, so “somewhere in there, the reality lies,” says Briony Horgan, a planetary scientist at Purdue University who wasn’t involved with the new study.

根據(jù)最初的水含量多少，新的模型估計(jì)，30%到99%的水都融入了地殼的礦物質(zhì)中，而其余部分則逃逸到了太空中。這是一個(gè)很大的范圍，而且這兩個(gè)過(guò)程可能都起了作用，所以“現(xiàn)實(shí)就存在于其中的某個(gè)地方，”普渡大學(xué)的行星科學(xué)家布里奧妮·霍根說(shuō)，不過(guò)她沒有參與這項(xiàng)新研究。

If the new model is accurate, then the story of the planet’s adolescence needs a rewrite. All of the water thought to be trapped in the Martian crust today means that the planet had far more surface water in its youth than previous models had estimated—and that early epoch may have been even more amiable to microbial life than previously thought.

如果新的模型是準(zhǔn)確的，那么地球處于青春期的理論就需要推翻重寫?，F(xiàn)如今所有被認(rèn)為是被困在火星地殼中的水意味著這個(gè)星球在其年輕時(shí)期的地表水比以前的模型所估計(jì)的要多得多，而且也意味著早期時(shí)代的火星可能比以前認(rèn)為的更適合微生物生命。

From drenched to desiccated

從濕透變成干燥

Hydrogen is still escaping from Mars today, and scientists can measure the rate to work out how much water is being permanently lost. If this rate held steady over the past 4.5 billion years, it would be nowhere near enough to explain the disappearance of so much surface water, says lead author of the new study Eva Linghan Scheller, a doctoral student at Caltech.

時(shí)至今日，氫仍在從火星逃逸，科學(xué)家們可以通過(guò)測(cè)量其速度來(lái)計(jì)算出有多少水在永久流失。加州理工學(xué)院的博士生伊娃·林漢·謝勒是這項(xiàng)新研究的主要作者，他說(shuō)，如果這個(gè)速度在過(guò)去的45億年里一直保持穩(wěn)定的話，這將遠(yuǎn)遠(yuǎn)不足以解釋為何有這么多地表水從火星消失。

Another clue came courtesy of all the orbiters and rovers examining Mars’s rocks. Over the past Two decades, a lot of water-bearing minerals have been diScovered, including plenty of clays. At first, only patches were found here and there. But today, “we see evidence for a huge volume of hydrated minerals on the surface,” Horgan says.

另一條線索來(lái)自于所有檢查火星巖石的軌道飛行器和陸行器。在過(guò)去的二十年里，它們發(fā)現(xiàn)了大量的包括粘土在內(nèi)的含水礦物質(zhì)。起初，只在各處發(fā)現(xiàn)了一些小塊兒含水礦物質(zhì)。但最近，“我們看到了地表有大量水合礦物質(zhì)的證據(jù)。”霍根說(shuō)。

All those extremely old hydrated minerals suggest that, long ago, plenty of water was flowing across the ancient Martian soil—much more than the atmospheric deuterium signal indicated.

所有這些極其古老的水合礦物質(zhì)表明，很久以前是有大量的水曾流過(guò)古老的火星土壤的，而且比大氣中的重氫信號(hào)所顯示的要多得多。

Two ways to kill a planet

毀滅一個(gè)星球的兩種方法

One problem was that previous models didn’t adequately take into account the crust’s ability to lock up water inside minerals, Scheller says. She and her colleagues decided to make a new model to estimate where Mars’s water went over its entire 4.5-billion-year lifetime.

謝勒說(shuō)，之前的一個(gè)問題是以前的模型沒有充分考慮到地殼將水鎖在礦物質(zhì)內(nèi)部的能力。她和她的同事們決定建立一個(gè)新的模型來(lái)估計(jì)火星上的水在其45億年的生命周期中都是在哪里流動(dòng)的。

The model makes some assumptions, such as how much water Mars had to begin with, how much was delivered later by watery asteroids and icy comets, how much was lost to space over time, and how much volcanic activity deposited more water onto the planet’s surface. Depending on the values of those variables, the team found that Mars could once have had enough surface water to make a global ocean 330 to 4,900 feet deep.

該模型做了一些假設(shè)，比如火星一開始有多少水，有多少水后來(lái)由含水的小行星和冰冷的彗星輸送，有多少水隨時(shí)間流失到太空，有多少火山活動(dòng)使更多的水沉積在火星表面等。根據(jù)這些變量的值，研究小組發(fā)現(xiàn)，火星曾經(jīng)有足夠的地表水，水量足以形成一個(gè)330到4900英尺深的全球海洋。

BeTween 4.1 and 3.7 billion years ago, the amount of surface water decreased significantly as it was soaked up by minerals in the crust and as it escaped into space. None of the hydrated minerals found so far have been younger than three billion years, Scheller says, which implies that Mars has been an arid wasteland for most of its lifetime.

41億至37億年前這段時(shí)間內(nèi)，地表水的數(shù)量顯著減少，因?yàn)樗坏貧ぶ械牡V物質(zhì)吸收了，還有的水逃逸到了太空中。謝勒說(shuō)，到目前為止，發(fā)現(xiàn)的含水礦物質(zhì)的年齡沒有一種是小于30億年的，這意味著火星在其生命的大部分時(shí)間里都是一片干旱的荒原。

“What this study does is that it says you have more water to play with early in Mars’s history, and that’s when Mars was most habitable,” Siebach says. Microbes, if they ever existed, may have spread through all that available water, but they would have struggled to survive by the time most of it vanished three billion years ago.

“這項(xiàng)研究表明，在火星早期的歷史中，有更多的水可以利用，那時(shí)的火星是最適宜居住的時(shí)期，” 西巴赫說(shuō)。如果微生物曾經(jīng)存在過(guò)的話，它們可能會(huì)擴(kuò)散到所有可用的水里去，但在30億年前大部分水消失的時(shí)候，它們會(huì)掙扎著生存下去。

Water binds to Earth’s minerals, too. But on our planet, plate tectonics recycles these minerals, constantly unleashing their water through volcanic eruptions, Siebach says. By contrast, Mars’s stagnant crust may have doomed the planet to become a bitterly cold desert. Did the same world-changing process happen on Venus? Does water end up locked in the crust of exoplanets far from our solar system?

水也可以與地球上的礦物質(zhì)結(jié)合。西巴赫表示，但是在我們的星球上，板塊構(gòu)造使這些礦物質(zhì)循環(huán)起來(lái)了，地殼通過(guò)火山爆發(fā)不斷釋放內(nèi)部的水。相比之下，火星不活躍的地殼可能注定了這個(gè)星球會(huì)變成一個(gè)寒冷的沙漠。同樣的世界改變過(guò)程在金星上也發(fā)生過(guò)嗎?水最終會(huì)被鎖在遠(yuǎn)離我們太陽(yáng)系的系外行星的地殼中嗎?

Scott King, a planetary scientist at Virginia Tech who wasn’t involved with the work, says that the model paves the way for an even richer understanding of how Mars and other rocky worlds evolve through the ages.

弗吉尼亞理工大學(xué)的行星科學(xué)家斯科特·金沒有參與這項(xiàng)工作，但他說(shuō)，這個(gè)模型為更豐富地了解火星和其他巖石世界在各個(gè)時(shí)代的演化過(guò)程鋪平了道路。