A new animation byNASA scientists illustrates what Mars – the fourth planet from the Sun and thesecond smallest planet in the Solar System – may have looked like billions ofyears ago.Today, Mars is a cold, desert world. Liquid water cannotexist pervasively on its surface due to the low atmospheric pressure andsurface temperature, although there is evidence for spurts of liquid flow thatperhaps consist of a briny solution with reduced freezing temperature. Waterunder current conditions can be ice or sublimate directly into vapor withoutstaying in a liquid phase.

据sci-news网站11月18日报道， 今天的火星是寒冷荒芜的世界。由于气压和表面温度低，液态水根本无法存在，不是变成冰，就是直接升华为蒸气。不过，40亿年前的火星可不是这样。那时它还很年轻，有着厚厚的大气层，这让火星温度适宜，水也能够存在，而水是生命的象征。

Around 4 billions ofyears ago when the planet was young, it appears to have had a thick atmospherethat was warm enough to support oceans of liquid water – a critical ingredientfor life.

美国航空航天局（NASA）科学家日前发布了一个新动画短片，推演了火星40亿年前的模样。动画向人们展示了蓝天、白云和清澈的湖水，这似乎是地球上某处风景秀丽之地。但你绝对很难想象，这很可能就是40亿年前的火星。