火星上很久沒(méi)下雨了，但這些沙丘看起來(lái)像雨滴

火星上很久沒(méi)下雨了，但這些沙丘看起來(lái)像雨滴

Mars is well-known for being a dry and arid place, where dusty red sand dunes are prevalent and water exists almost entirely in the form of ice and permafrost.

眾所周知，火星是一個(gè)非常干燥的地方，那里到處都是布滿灰塵的紅色沙丘，水幾乎完全以冰和永久凍土的形式存在。

An upside to this, however, is the fact that these conditions are the reason why Mars' many surface features are so well preserved. And as missions like the Mars Reconnaissance Orbiter (MRO) have shown, this allows for some pretty interesting finds.

然而，有利的一面是，這些條件正是火星的許多表面特征得以如此完好保存的原因。就像火星勘測(cè)軌道飛行器(MRO)這樣的任務(wù)所顯示的那樣，這使得一些非常有趣的發(fā)現(xiàn)成為可能。

Consider the picture recently taken by Curiosity's High Resolution Imaging Science Experiment (HiRISE) instrument while orbiting above the Copernicus Crater on Mars.

想想最近好奇號(hào)的高分辨率成像科學(xué)實(shí)驗(yàn)(hirise)儀器，在火星哥白尼隕石坑上方繞軌道飛行時(shí)拍攝的照片。

This image showed raindrop-like features that are actually signs of sand dunes that are rich in olivine. These same types of dunes exist on Earth but are very rare since this mineral weathers quickly and turns to clay in wet environments.

這張圖片顯示了雨滴狀的特征，這實(shí)際上是沙丘富含橄欖石的跡象。這些相同類(lèi)型的沙丘在地球上存在，但非常罕見(jiàn)，因?yàn)檫@種礦物的氣候變化很快，在潮濕的環(huán)境中會(huì)變成粘土。

Olivine is used by geologists to describe a group of rock-forming minerals that are typically found in igneous rocks. This mineral is so-named because of its green color, which is due to its chemical composition – silicate-based (SiO4) and bonded with either Magnesium or Iron (Mg2SiO4; Fe2SiO4).

橄欖石被地質(zhì)學(xué)家用來(lái)描述一組典型地存在于火成巖中的造巖礦物。這種礦物之所以如此命名，是因?yàn)樗木G色是由它的化學(xué)成分——硅酸鹽基(SiO4)，并與鎂或鐵(MG2SiO4;Fe2SiO4)結(jié)合。

On Earth, it is generally found in dark-colored igneous rocks and is one of the first minerals to crystalize during the slow cooling of magma.

在地球上，它普遍存在于深色火成巖中，是巖漿緩慢冷卻過(guò)程中首先結(jié)晶的礦物之一。

(NASA/JPL/University of Arizona)

However, it is a rare thing to find so many sand dunes that are rich in olivine deposits on Earth, as was imaged by the MRO. The reason for this is because olivine is one of the weaker common minerals on Earth's surface and quickly turns into a combination of clay minerals, iron oxides and ferrihydrites (iddingsite) in the presence of water.

然而，像MRO所拍攝到的那樣，在火星上發(fā)現(xiàn)如此多富含橄欖石沉積物的沙丘，實(shí)屬罕見(jiàn)。這是因?yàn)殚蠙焓腔鹦潜砻孑^弱的常見(jiàn)礦物之一，在有水存在的情況下，橄欖石會(huì)迅速變成粘土礦物、氧化鐵和鐵素體(iddingsite)的結(jié)合體。

However, deposits of olivine have been found in meteorites, on the Moon, Mars, and even on the asteroid Itokawa (which was visited by the Japanese Hayabusa mission in 2005). Since asteroids and meteorites are essentially leftover material from the formation of the Solar System, this would suggest that olivine minerals were present at the time.

然而，在隕石、月球、火星，甚至是小行星伊藤川(2005年日本隼鳥(niǎo)任務(wù)訪問(wèn)過(guò))上都發(fā)現(xiàn)了橄欖石的沉積物。由于小行星和隕石基本上是太陽(yáng)系形成過(guò)程中遺留下來(lái)的物質(zhì)，這可能表明當(dāng)時(shí)存在橄欖石礦物。

In addition, the presence of iddingsite on Mars and the Moon is a strong indication that liquid water once existed there. By studying deposits of olivine and it's by-products, scientists might be able to determine when Mars made the transition from having liquid water on its surface to the very dry place that it is today.

此外，火星和月球上的iddingsite的存在是液態(tài)水曾經(jīng)存在的有力證據(jù)。通過(guò)研究橄欖石及其副產(chǎn)品的沉積，科學(xué)家們可能能夠確定，火星是何時(shí)從表面有液態(tài)水轉(zhuǎn)變到今天非常干燥的地方。

In the meantime, the discovery of these many dunes on Mars is a testament to how well certain features have been preserved over time. If there was indeed wind and water erosion on Mars as their is on Earth, the Copernicus Crater would have become a clay-rich region very quickly.

與此同時(shí)，火星上這些沙丘的發(fā)現(xiàn)證明了隨著時(shí)間的推移，某些特征被保存得有多好。如果火星上真的像地球上一樣有風(fēng)和水的侵蝕，哥白尼隕石坑會(huì)很快變成富含粘土的區(qū)域。

As always, Mars dazzles us with unique combination of similarities and differences to Earth!

一如既往，火星以其獨(dú)特的相似性和差異性使我們眼花繚亂!