Giant Tsunami Remnants Spotted on Mars
火星上发现海啸痕迹

Evidence indicates that waves as tall as skyscrapers and thousands of kilometers wide once washed over the Red Planet.
有证据表明，高如摩天大厦，宽数千公里的浪潮一度席卷过这个红色的星球。

播音/撰文：Lee Billings
翻译：bing
审校：吴非

For as long as we’ve been sending spacecraft to Mars, we’ve been finding signs of water. The Red Planet’s sinuous river valleys, flood-carved canyons and buried glaciers all hint that it was wet billions of years ago.
自从我们将探测器送往火星开始，就不断发现火星曾存在水的迹象。弯曲的河谷、洪水雕刻出的峡谷、埋藏在地表下的冰川均暗示着，在数十亿年前，火星曾是一颗湿润的星球。

Some researchers think that the curiously flat and sparsely cratered northern lowlands are the remnants of a once-great ocean. But that ocean’s proposed coast varies in height by thousands of meters, which has made the idea controversial.
Now, a team of researchers has found evidence for ancient tsunamis on Mars, evidence that supports the idea of a vanished Martian ocean and explains its vertically variable shoreline.
在火星的北方有一片平坦而少有陨石坑的低地，一些研究人员认为，这块神秘地带曾是一片广袤的海洋。然而，推测的海岸线有几千米的高度差，这又使得这个观点自相矛盾。
但现在，一个研究团队发现了火星上曾有海啸存在的证据，这就可以证明火星原本存在一片海洋，同时可以解释为什么海岸线有巨大的高度差。

“We were trying to find shorelines on Mars like those we typically see on Earth, which is consistently distributed along a constant elevation. And that is not what we have found on Mars, because in the case of Mars the shorelines were buried beneath the tsunami deposits.”
“我们试图在火星上寻找海岸线，我们曾认为它们和地球上的海岸线一样，在同一海拔上连续分布。但我们却没找到类似的海岸线，因为它们被埋藏在海啸沉积物下方。”

Alexis Rodriguez of the Planetary Science Institute in Tucson. He led a team that used satellite images to identify thick deposits of boulders and silt apparently left by two separate tsunamis, a few million years apart, almost three-and-a-half billion years ago.
Alexis Rodriguez在位于图森的行星科学研究所工作，他带领团队通过卫星图像来识别沉积物中的砾石和淤泥，这些物质是两次约35亿年前的海啸过后的残留物，这两次海啸间隔数百万年。

“The discovery of the tsunami deposits represents definite evidence for the existence of the early Martian ocean….the tsunamis were enormous. On average we estimate they were about 50 meters in height, but at some locations they could have reached as much as 120 meters...and the surface areas that the tsunamis covered within the study region are also huge…each tsunami had roughly the combined areas of California, Nevada and Oregon.”
“海啸沉积物有力地证明，在早期的火星上存在海洋。这两次海啸的威力巨大。我们估计，它们的平均高度是50米，但在一些地方，它们可以高达120米。此次研究中，海啸波及的范围很广，每次海啸事件影响的面积大致相当于加利福尼亚州、内华达州和俄勒冈州的面积之和。”

The most plausible cause for such massive tsunamis was asteroids or comets slamming into the Martian ocean. The study is in the journal Scientific Reports. [J. Alexis P. Rodriguez et al., Tsunami waves extensively resurfaced the shorelines of an early Martian ocean]
造成这两次海啸的头号疑凶是小行星或彗星撞击火星。该研究发表在《科学报告》杂志中。

The tsunamis could provide crucial information about the habitability of ancient Mars. The first one occurred when the planet must have been relatively warm and amenable for life, because it carved out backwash channels as it returned to the sea. By contrast, the planet had become much cooler by the time the second tsunami hit—the waters apparently flash-froze after flowing onto the surface.
Examining additional tsunami deposits could reveal much more data about Mars’s ancient climate changes. Someday, rovers—or astronauts—might even visit the deposits, looking for evidence of past marine life locked in frozen waves.
—Lee Billings
海啸可以帮助我们了解，古时的火星是否适合生存。海啸第一次发生时，当时火星的环境一定相对温暖、适合生存，因为当海啸退去时，它会在海岸刻下退潮的通道。相反，当海啸第二次侵袭时，火星上的温度更低，很明显，海水在流过海岸时结冰了。检测更多的海啸残留物，会为我们研究火星的古气候变化提供更多数据。终有一天，火星车或宇航员可能会见到这些沉积物，寻找被冰封的古火星生物痕迹。