Today it looks like many of the arid deserts here on Earth. It was formed from the same stuff and evidence shows that it once had plenty of liquid water, that was around four billion years ago, Mars had a strong magnetic field, created, just like Earth’s, by convection currents of molten metals in the planet’s core. But, unlike Earth, Mars (being much smaller than Earth) cooled enough internally to switch off that mechanism, and the planet ended up with very little global magnetic field. Without a strong magnetic field, the planet was less protected from the solar wind – the streams of energetic charged particles flowing from our Sun. The solar wind stripped away most of the Martian atmosphere in only a few hundred million years after Mars slowly lost its magnetic field. The loss of a large fraction of its atmosphere to space was a major cause of Mars’s transition from a warm, wet climate to today’s cold, dry one. As for the colour, most of the colours we see are from the dust that contains levels of iron oxide (rust). When the rover drills into these rocks we see the true colours of the rocks, many are different shades of grey (just like on Earth) others are tones of red. I’ve attached a composite image featuring the first 42 holes drilled by Curiosity since it landed in August 2012, see all the different colours (under the thin coating of red dust.