時差N小時:火星上的海洋

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

唐：嘿，雅艾爾，你聽說過嗎，我們發(fā)現(xiàn)了兩處新大洋?

Yael: Where?

雅艾爾：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?，F(xiàn)在它們已經(jīng)不復(fù)存在了，但是幾十億年前它們確實在那里。

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

雅艾爾：我還以為科學(xué)家們不確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 thatwere left behind when standing water evaporated. It also discovered cross-bedding in the soilwhich was created by water ripples, and tiny mineral deposits called blueberries that onlyappear if water is present. The northern lowlands of Mars looked like there might have been anocean there, but there wasn't definite proof.

唐：以前不確定。機(jī)遇號火星探測器在土壤里發(fā)現(xiàn)了靜水蒸發(fā)后留下硫酸鹽和其它鹽類。同時還在土壤中發(fā)現(xiàn)了水波產(chǎn)生的交錯層，以及稱之為藍(lán)莓的小型礦床，而這種礦床只存在于有水的地方。火星北部低地正好具備這些特征，因此斷定這里之前可能是海洋，但是還沒有確鑿的證據(jù)。

Yael: So, what has changed their minds?

雅艾爾：那么，是什么讓他們改變了主意?

Don: Gamma Ray evidence.

唐：伽馬射線發(fā)現(xiàn)的證據(jù)。

Yael: That sounds exciting.

雅艾爾：聽起來很令人興奮。

Don: It is. The Mars Odyssey spacecraft had a gamma-ray spectrometer onboard that coulddetect 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 ironabove and below what they thought to be the shoreline of ancient oceans. They expected to seelow concentrations above the shoreline and larger concentrations below. That would indicatethat the elements had been leached out of the soil by the water.

唐：的確。奧德賽火星探測器內(nèi)設(shè)有伽馬射線光譜儀主板，能夠探測到地下三分之一米(或者13英尺)的元素構(gòu)成?？茖W(xué)家們利用光譜儀來測量鉀、釷和鐵的分布，看它們是高于還是低于他們認(rèn)定的遠(yuǎn)古海洋的海岸線。他們期望看到密度低的元素高于海岸線，而密度高的元素低于海岸線。如果是的話，就表明這些元素是被水沖刷才浸出土壤的。

Yael: So, what did they find?

雅艾爾：那么，他們發(fā)現(xiàn)了什么?

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

唐：他們發(fā)現(xiàn)較年輕的那片海洋的海岸線是地中海的十倍，而較古老的海洋則是地中海的兩倍。

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

雅艾爾：真是太糟糕了，這些海洋都不在了。

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

唐：是呀。要不然它肯定會成為巡游的好地方。