The most powerful camera that has ever been used to survey another planet is capturing spectacular pictures of the surface of Mars to reveal a rich tapestry of geological features. Located on board the Mars Reconnaissance Orbiter, a Nasa probe launched in 2005, the HiRise camera has already taken detailed images of the outlines of ancient extra-terrestrial seas and rivers – the first unambiguous evidence that shorelines once existed on the Red Planet.
The camera has also witnessed in high-resolution detail the moment when the warmth of the Martian spring forced puffs of dust through the thin polar caps of dry ice – solid carbon dioxide – to form weird "starburst" patterns on the surface of the planet.
"Spring on Mars is quite different from spring on Earth because Mars has not just permanent ice caps, but also seasonal polar caps of carbon dioxide," said Candice Hansen-Koharcheck, of Nasa's Jet Propulsion Laboratory in Pasadena, California.
"What happens on Mars, we think, is that as the seasonal ice cap thins from the bottom, gas underneath the cap builds up pressure. And where gas under the ice finds a weak spot or a crack, it will flow out of the opening, often carrying a little dust from the surface below."
In addition to operating in the visible light spectrum, the HiRise camera can "see" in near-infrared regions enabling it to gather information on the mineral content of the rocks and dust that form the Martian landscape. Its telescopic lens gives it an unprecedented resolution for a space-probe camera, enabling it to distinguish surface features as little as four feet wide.
Such high-resolution images have enabled the Mars Reconnaissance Orbiter to build up an impressive library of landscape views showing richly layered materials, gullies and eroded channels, some perhaps formed in very recent times by running water. Nasa scientists believe the information will be invaluable if they ever have to choose a landing site for a possible manned mission to Mars later this century.
The Mars Reconnaissance Orbiter was designed to make a detailed survey of the Martian surface, as well as its immediate subsurface and its atmosphere. The mission goals of the probe are to determine whether life ever arose on Mars, to characterise the planet's climate and geology, and to prepare for possible human exploration by locating, for instance, existing pockets of water that future astronauts could exploit for their life-support systems.
But the biggest of all questions was whether liquid water was ever around long enough to provide a basis for extra-terrestrial life to have originated and evolved. Although it is clear that water did once exist on Mars, and may still exist under its frozen surface, the question of life itself is still unresolved.
"While other Mars missions have shown that water flowed across the surface in Mars's history, it remains a mystery whether water was ever around long enough to provide a habitat for life. Mars Reconnaissance Orbiter will study the history of water on Mars," said a Nasa spokesman.
It took the orbiter seven months to cruise to Mars followed by a further six months of careful "aerobraking" to get the spacecraft into precisely the right orbit to make its scientific observations. Following on from the previous Nasa orbiter, the Mars Global Surveyor, which finally died in April 2007 after battery failure, the Orbiter will make the most detailed geological survey of the Red Planet to date.