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Part of the reason may be that NASA has been crying wolf before. The 'arsenic life' announcement wasn't that long in the past. So people may be a bit wary until

• bootload 14y ago
  "... So people may be a bit wary until the images have been independently analysed...." Good point. The theory of a flowing river should support all types of evidence at large & small scale: alluvial fans, "... The imagery shows an alluvial fan of material washed down from the rim, streaked by many apparent channels, sitting uphill of the new finds. ..." to pebbles and rate of flow of liquids, "... From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep... This is the first time we're actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it. ..." All directly observable evidence, each piece confirming the conclusion.