On Aug. 6, the most advanced machine ever sent to another world landed successfully on Mars. Within hours of its touchdown in the Gale Crater, NASA's Curiosity rover was transmitting black-and-white images of the Martian landscape, the first of what scientists predict will be literally millions of bits of information about the planet.

In fact, scientists did not have to wait long for the first significant discovery by Curiosity. By Sept. 27, Curiosity had confirmed what scientists have long suspected — that water anywhere from ankle to waist deep once flowed on Mars' surface.

The conclusion, scientists said, is based on images showing what looks like an ancient gravel stream bed. One of the stream bed slabs appears to be made of gravel cemented together by water that once ran freely on Mars and settled on the floor of Gale Crater, likely several billion years ago.

Mission scientist WiIliam Dietrich, of the University of California, Berkeley, said it looks like the water was moving at about 3 feet (0.91 meters) per second, "with a depth somewhere between ankle and hip deep." Dietrich said there have been a lot of theories about water flows on Mars, but "this is the first time we're actually seeing water-transported gravel on Mars."

The evidence that a warmer and wetter Mars once enjoyed floods of water inside Gale Crater adds to the US$2.5 billion (approximately NT$73 billion) rover's efforts to find evidence that Mars was once capable of supporting life.

Essentially, the rover is now traveling over stones that were washed down from a canyon on the crater wall "several billion years ago," said Michael Malin of the rover imaging team. Most likely the canyon waters flowed sporadically over thousands to millions of years, depositing gravel in a broad fan of stones covering the floor of the crater.

The rover is equipped with a laser, drill and on-board lab to investigate the chemistry of Martian rocks. The final goal of the rover is to examine layers of clay that underlay the foothills of Mount Sharp, the 3.4-mile-high (5.5-kilometer-high) mountain in the center of Gale Crater. It is expected to arrive in those foothills in about a year as its bold mission continues.