时差N小时 火星上的海洋（在线收听）

Don: Hey, Yael, Have you heard We've discovered two new oceans?

唐：嘿，雅艾尔，你听说过吗，我们发现了两处新大洋？

Yael: Where?

雅艾尔：在哪里？

Don: On Mars. Well, they aren't there any longer, but they were there a few billion years ago.

唐：在火星上。现在它们已经不复存在了，但是几十亿年前它们确实在那里。

Yael: I thought scientists weren't sure if Mars had oceans or not.

雅艾尔：我还以为科学家们不确定火星上是否有海洋。

Don: They weren't. The Mars Opportunity Rover found sulfates and other salts in the soil that were left behind when standing water evaporated. It also discovered cross-bedding in the soil which was created by water ripples, and tiny mineral deposits called blueberries that only appear if water is present. The northern lowlands of Mars looked like there might have been an ocean there, but there wasn't definite proof.

唐：以前不确定。机遇号火星探测器在土壤里发现了静水蒸发后留下硫酸盐和其它盐类。同时还在土壤中发现了水波产生的交错层，以及称之为蓝莓的小型矿床，而这种矿床只存在于有水的地方。火星北部低地正好具备这些特征，因此断定这里之前可能是海洋，但是还没有确凿的证据。

Yael: So, what has changed their minds?

雅艾尔：那么，是什么让他们改变了主意？

Don: Gamma Ray evidence.

唐：伽马射线发现的证据。

Yael: That sounds exciting.

雅艾尔：听起来很令人兴奋。

Don: It is. The Mars Odyssey spacecraft had a gamma-ray spectrometer onboard that could detect elements buried as much as a third of a meter, or thirteen inches, below the soil. Scientists used the spectrometer to measure the amount of potassium, thorium, and iron above and below what they thought to be the shoreline of ancient oceans. They expected to see low concentrations above the shoreline and larger concentrations below. That would indicate that the elements had been leached out of the soil by the water.

唐：的确。奥德赛火星探测器内设有伽马射线光谱仪主板，能够探测到地下三分之一米（或者13英尺）的元素构成。科学家们利用光谱仪来测量钾、钍和铁的分布，看它们是高于还是低于他们认定的远古海洋的海岸线。他们期望看到密度低的元素高于海岸线，而密度高的元素低于海岸线。如果是的话，就表明这些元素是被水冲刷才浸出土壤的。

Yael: So, what did they find?

雅艾尔：那么，他们发现了什么？

Don: They found the shorelines of a younger ocean about ten times the size of the Mediterranean Sea, and an older ocean twice that size.

唐：他们发现较年轻的那片海洋的海岸线是地中海的十倍，而较古老的海洋则是地中海的两倍。

Yael: It's too bad those oceans still aren't there.

雅艾尔：真是太糟糕了，这些海洋都不在了。

Don: Yeah. It sure would be a great spot for a cruise.

唐：是呀。要不然它肯定会成为巡游的好地方。