火星新月形沙丘

On Jan. 16, 2020, the Mars Reconnaissance Orbiter (MRO) captured this image of two types of sand dunes on Mars: barchan and linear dunes.

The small dots are called barchan dunes, and from their shape we can tell that they are upwind. The downwind dunes are long and linear. These two types of dune each show the wind direction in different ways: the barchans have a steep slope and crescent-shaped “horns” that point downwind, while the linear dunes are stretched out along the primary wind direction. Linear dunes, however, typically indicate at least two different prevailing winds, which stretch out the sand along their average direction.

Barchan and linear dunes aren’t just a Martian phenomenon – we can also see them on Earth. Astronauts aboard the International Space Station have snapped photos of them occurring in Brazil and Saudi Arabia.

Image Credit: NASA/JPL-Caltech/University of Arizona

2020年1月16日，火星勘测轨道器（MRO）拍摄到了火星上两种类型的沙丘：新月形沙丘和线形沙丘。

小点状的被称为新月形沙丘，从它们的形状我们可以判断它们是逆风的。顺风沙丘是长而线形的。这两种类型的沙丘都以不同的方式显示了风向：新月形沙丘有陡峭的坡度和指向顺风的新月形“角”，而线形沙丘则沿着主要风向伸展。然而，线形沙丘通常表明至少两种不同的盛行风，这些风向将沙子沿其平均方向延展。

新月形沙丘和线形沙丘不仅仅是火星上的现象——我们也可以在地球上看到它们。国际空间站上的宇航员已经拍摄了发生在巴西和沙特阿拉伯的这些沙丘的照片。

影像来源：NASA/JPL-Caltech/University of Arizona