在撒哈拉沙漠发现的一块陨石，是一块41亿年前的火星岩石。这块太空岩石中的矿物为红色星球的早期历史提供了线索，那时火星表面有水流动。
A Meteorite Found in the Sahara Is a 4.1-Billion-Year-Old Piece of Mars Minerals in the space rock provide hints about the early history of the red planet, when water was flowing on the surface.
四年前在撒哈拉沙漠发现的红褐色岩石，其年龄比地球上几乎所有事物都要古老。事实上，它们并非来自地球：它们是可追溯至41亿年前的火星碎片。
Reddish rocks found in the Sahara four years ago turned out to be older than almost anything on Earth. In fact, they are not of this world: They are pieces of Mars dating back 4.1 billion years.
科学家在周四发表于《科学》杂志的一篇论文中描述了这些陨石碎片。它们共同组成了一块名为“Teghaza 001”的太空岩石，该名称源自马里境内一个古老、已废弃的盐矿聚落特加扎，碎片即在该聚落附近被发现。
Scientists described the meteorite fragments in a paper published on Thursday in the journal Science. Together they make up a space rock named Teghaza 001, after an ancient, abandoned salt-mining settlement in Mali close to where the fragments were found.
“发现如此古老的物质非常罕见，”美国国家航空航天局喷气推进实验室的行星科学家、该《科学》论文的第一作者杨柳（Yang Liu，音译）表示。
“It’s very rare to find something this old,” said Yang Liu, a planetary scientist at NASA’s Jet Propulsion Laboratory in California and the lead author of the Science paper.
在已发现的400多块火星陨石中，只有两块——艾伦山84001号和西北非洲7034号（常被称为“黑美人”）——其年龄能与Teghaza 001相媲美。
Of the more than 400 Martian meteorites that have been found, only two, Allan Hills 84001 and Northwest Africa 7034, which is often called “Black Beauty,” rival Teghaza 001 in age.
对科学家而言，Teghaza 001宛如一台时光机。其火成矿物的混合保存了火星形成后数亿年时期的快照。这些矿物为早期火星的地幔和地壳提供了线索。
For scientists, Teghaza 001 serves as a time machine. Its mix of igneous minerals preserves a snapshot of what Mars was like a few hundred million years after it formed. The minerals provide hints about both the mantle and the crust of early Mars.
“我们的火星收藏中确实没有这种矿物学特征，”内华达大学拉斯维加斯分校地球科学教授阿里亚·乌德瑞（Arya Udry）说，她未参与这项研究。“任何来自火星的独特新岩石都令人非常兴奋。”同一批科学家此前发表的一篇论文报告称，该陨石包含证据，表明当这块岩石形成时，火星上曾有大量水流动，这是基于一种名为磷灰石的矿物中结合的水分子。
“We really don’t have this kind of mineralogy in our Martian collection,” said Arya Udry, a professor of geoscience at the University of Nevada, Las Vegas, who was not involved in the research. “Any new rock that is unique from Mars is really exciting.”An earlier paper by some of the same scientists reported that the meteorite contained evidence that abundant water flowed on Mars when the rock formed, based on water molecules bound within a mineral known as apatite. (The Martian apatite is similar to the mineral that is the main ingredient of your teeth.)
（火星磷灰石与构成你牙齿主要成分的矿物相似。）但分析也显示，这颗行星当时已经失去了大部分水分。紫外线将水分子分解为氢和氧，氢气飘散到太空中。
But the analysis also showed that the planet had already lost much of its water. Ultraviolet light broke apart the water molecules into hydrogen and oxygen, and the hydrogen floated away into space.
这块陨石的旅程始于一颗陨星撞击火星，将这块岩石击入太空。最终，它与地球相遇。一块重近两磅的岩石碎片在穿越大气层的烈火中幸存下来。它作为陨石着陆，并破碎成八块。
The meteorite’s journey began when a meteor hit Mars, knocking the rock into space. Eventually, it crossed paths with Earth. A chunk of the rock weighing nearly two pounds survived the fiery entry through the atmosphere. It landed as a meteorite and broke into eight pieces.
当刘博士首次收到这块陨石样本进行研究时，她并不指望它会很有趣。它最初被归类为舍尔戈蒂陨石——这是最常见的火星陨石类型，通常年代不算太久远。
When Dr. Liu first received the meteorite sample to study, she did not expect it to be very interesting. It had been initially classified as a shergottite — the most abundant type of Martian meteorite and one that is usually not that old.
但当她观察时，发现了锆石，这是一种通常不在舍尔戈蒂陨石中发现的晶体。“这非常不寻常，而且我在样本中看到了很多，”她说。“这立刻敲响了警钟。”利用一种基于铀同位素比率的测年方法，科学家们得知这些锆石约有41亿年历史。另外两种测年方法确认了这一年龄。
But when she looked, she saw zircons, a type of crystal that is usually not found in shergottites. “It’s very unusual, and I see a lot of them in the sample,” she said. “That was a quick alarm bell going off.”Using a dating method based on the ratio of uranium isotopes, the scientists learned that the zircons were about 4.1 billion years old. Two other dating methods confirmed the age.
“一旦我们确认这个特加扎样本是一块古老的岩石，我们立即对尝试表征其水分特征产生了浓厚兴趣，”在加利福尼亚州山景城美国宇航局艾姆斯研究中心工作的行星科学家李·萨珀（Lee Saper）说，她也是这两篇特加扎论文的另一位作者。
“Once we recognized that this Teghaza sample was an ancient one, we immediately became interested in trying to characterize its water,” said Lee Saper, a planetary scientist working at the NASA Ames Research Center in Mountain View, Calif., and another author of the two Teghaza papers.
磷灰石中的水似乎来自两个不同的来源。部分水存在于从火星地幔上升的岩浆中。
The water in the apatite appears to have come from two different sources. Some of the water was in the magma that rose from the Martian mantle.
刘博士表示，特加扎001地幔部分的元素组合看起来与其他火星陨石测量结果显著不同。“这表明它更为原始，未受后期过程影响，”她说。
Dr. Liu said the mix of elements of the mantle portion of Teghaza 001 looked significantly different from what had been measured in other Martian meteorites. “Which is suggesting it’s more primordial, not affected by later processes,” she said.
其他水分子来自地表和大气，渗透穿过地壳。科学家们能够判断火星上大部分水已逃逸到太空，因为这些分子拥有更高浓度的氘——氢的较重同位素，不太可能飘散逃逸。
Other water molecules came from the surface and the atmosphere, percolating through the crust. The scientists could tell that much of the water on Mars had already escaped to space, because those molecules possessed a higher concentration of deuterium, the heavier version of hydrogen, which is less likely to float away.
特加扎001中的氘与普通氢比率与在艾伦山84001中发现的相似。“这并没有完全改变我们对当时火星的看法，但现在我们有了两个数据点而不是一个，这让我们更有信心，”萨珀博士说。
The deuterium-to-ordinary-hydrogen ratio in Teghaza 001 is similar to what was found in Allan Hills 84001. “It’s not completely changing our view of Mars at that time, but now we have two data points instead of one, which gives us a lot more confidence,” Dr. Saper said.
目前不确定这块岩石何时被撞击抛入太空，也不确定何时落入撒哈拉沙漠。但通过将陨石的矿物学特征与机器人航天器从火星轨道测量的数据进行比对，研究人员已确定了特加扎001可能源自的13个地点。
It is not certain when the rock was knocked into space or when it landed in the Sahara. But by comparing the mineralogy of the meteorite with what robotic spacecraft have measured from orbit around Mars, the researchers have identified 13 locations where Teghaza 001 could have originated.
研究人员表示期待其他科学家进行进一步分析。“我们只研究了它的一小部分，”萨珀博士说。“还有更复杂的故事有待揭示。”肯尼斯·张是《纽约时报》的科学记者，报道美国国家航空航天局（NASA）和太阳系，以及更贴近地球的研究。
The researchers said they looked forward to additional analysis by other scientists. “We looked at a small part of it,” Dr. Saper said. “There’s a much more complex story that’s yet to be uncovered.”Kenneth Chang, a science reporter at The Times, covers NASA and the solar system, and research closer to Earth.