Mars today is a freezing desert, but it wasn鈥檛 always so. A new analysis shows that rivers flowing on the planet鈥檚 surface 1 billion years ago were wider than those found on Earth today.
Evidence collected by rovers and orbiting spacecraft has shown that Mars鈥檚 surface was once covered with lakes and rivers, but we don鈥檛 know exactly when they dried up. It is thought that about 4 billion years ago, the planet聽started to lose its atmosphere and thus its water.
To study how wet Mars once was, Edwin Kite at the University of Chicago, Illinois, and his colleagues measured the widths of 205 well-preserved river channels there, based on high-resolution images taken by orbiters. They looked at the width of these channels, along with the size of the river basins 鈥� the area in which all precipitation, snowmelt and groundwater drains into a particular river.
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The team found that, for a given basin size, rivers on Mars were more than twice as wide as Earth鈥檚. Channels are shaped by their peak water level during floods, and if Mars鈥檚 climate and water cycle had worked similarly to Earth鈥檚, we should expect similar river widths on both planets.
Moreover, the team found that Martian rivers that formed 1 billion years ago had similar sizes to those formed before the planet lost its atmosphere. This suggests the drying-out of Mars didn鈥檛 seem to affect the amount of water in these rivers, at least during peak seasons.
鈥淚 was totally surprised,鈥� says Kite. 鈥淢y first reaction was: 鈥楬uh that鈥檚 funny.鈥欌��
Further calculations show these young rivers were fed mainly by rainfall. Snowmelt alone wouldn鈥檛 have produced enough water. This means rain fell intensely on Mars, even when its atmosphere was thin.
鈥淔or reasons we don鈥檛 understand, land features on Mars tend to be larger than Earth鈥檚,鈥� says Victor Baker at the University of Arizona. 鈥淸The study] advances our understanding of past climate activities on Mars.鈥�
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