As announced a while ago, one of the most exciting discoveries by the Curiosity rover on Mars so far has been an apparent ancient streambed which once flowed right through the landing site. Now, additional examination of the evidence confirms that it is what it seemed to be – a very old, now long-dry, riverbed.
Even before the landing last year, it was thought likely that streams had once been active in the huge Gale crater, which Curiosity landed in. Channels cutting through the crater walls ended in what looked like alluvial fans, just like where a river on Earth ends and deposits gravel and silt.
As it turned out, Curiosity landed right on the outskirts of one of these alluvial fans. The images sent back by the rover showed what looked like typical streambed gravel. The gravel pebbles are rounded smooth just like those submerged in water on Earth. This gravel is also embedded in conglomerate rocks similar to those found in earthly rivers and streams, which allowed scientists to estimate how deep the water was and how fast it flowed.
As Rebecca Williams, of the Planetary Science Institute in Tucson and lead author of a new article in the journal Science, “We completed more rigorous quantification of the outcrops to characterize the size distribution and roundness of the pebbles and sand that make up these conglomerates. We ended up with a calculation in the same range as our initial estimate last fall. At a minimum, the stream was flowing at a speed equivalent to a walking pace – a meter, or three feet, per second – and it was ankle-deep to hip-deep.”
She adds, “These conglomerates look amazingly like streambed deposits on Earth. Most people are familiar with rounded river pebbles. Maybe you’ve picked up a smoothed, round rock to skip across the water. Seeing something so familiar on another world is exciting and also gratifying.”
The analysis also shows that the stream was fairly long-lived, although exactly how long it lasted isn’t known. It also flowed for several kilometres / miles. It is also thought that at least part of Gale crater was once a lake, which these streams emptied into.
Many old riverbeds have been seen on Mars from orbit, but this is the first time that one has actually been observed up-close. Mars was indeed once a much wetter place than it is today…
This article was first published on Examiner.com.