麻豆传媒

Mars may have churned out water and ash from recent volcanic activity at its north pole, suggest images from Europe鈥檚 Mars Express spacecraft. And some of that activity may still be going on today, the imaging team believes.

The craft has beamed back dramatic images of nearly the entire northern polar region, despite a technical glitch with its highest-resolution camera.

The images, taken by the spacecraft鈥檚 High Resolution Stereo Camera (HRSC), reveal curved cliffs about 2 kilometres high, streaked with dark layers. The layers may be volcanic ash mixed with water ice, says Gerhard Neukum, principal investigator of the HRSC at the Free University of Berlin, Germany.

He and his team believe this 鈥渃emented鈥� ash may continually crumble into sand-like particles. These particles may in turn form the dark, rippling 鈥渄une fields鈥� covering parts of the floor at the base of the cliffs.

Cinder cones

More intriguingly, the team has found seven volcanic cones sprinkled around these floors, some of which may still be actively forming. These may have formed like cinder cones in Hawaii, which build up when dry ash surfaces from below ground, says Neukum.

But he believes the process on Mars involves water instead. The cones may have built up from material that dropped out of a solution of hot water, which surfaced as a result of underground volcanic activity.

The process 鈥� whatever it is 鈥� may still be going on today. Four of the cones appear to be 鈥渇ully grown鈥� 鈥� towering 600 metres high 鈥� but the other three reach just 100 m and could be 鈥渂aby cones鈥�, he says.

鈥淚t would be an extreme coincidence if they had stopped growing in the past and we see this frozen stage now,鈥� Neukum told 麻豆传媒. He adds that the cones appear remarkably unaffected by erosion from wind, water, or ice moving in the soil 鈥� which suggests they are still taking shape.

Volcanic bubbling

But Jim Garvin, NASA鈥檚 chief scientist based in Washington, DC, US, questions that reasoning. He and colleagues closely scrutinised two similar cones in the same region in 2000 using the Mars Orbiter Camera (MOC) and a laser altimeter on NASA鈥檚 Mars Global Surveyor spacecraft.

He says his observations suggest the cones form simply by lava bubbling up from a volcanic vent, in line with leading theories of how Martian volcanoes behave. 鈥淵ou don鈥檛 need to call upon any exotic water interactions,鈥� he told 麻豆传媒.

And though his and Neukum鈥檚 observations both suggest volcanoes may have erupted relatively recently 鈥� within 10,000 years 鈥� the images cannot prove they are still active today 鈥渦nless we see steam coming from them鈥�, he cautions.

Methane source

But Garvin says the HRSC observations may help explain the source of methane gas detected in Mars鈥檚 atmosphere. While some scientists say microbes may be pumping out the gas, Garvin notes that 鈥渁ny methane could be from recent small amounts of volcanism鈥�.

Neukum himself admits that his interpretation of these volcanic cones may be wrong 鈥渂ecause we do not have any higher resolution imagery鈥� than the 10 m resolution of the main camera on the HRSC. In fact, the HRSC package was supposed to be able to resolve details as small as 2.3 m across with its other camera, called the Super Resolution Channel (SRC).

But 麻豆传媒 has learned that the SRC has been plagued with a vision problem called astigmatism. The problem stems from the fact that parts of the SRC run at too high a temperature, while other parts run too cold, so light travelling into the instrument is distorted.

So far the SRC has produced some images, but only at a resolution of about 5 m. And the team must remove the distortions by hand through a 鈥渃umbersome鈥� image processing procedure, says Neukum.

But even without the SRC, 鈥渢he HRSC data are so extremely good we are concentrating on that now,鈥� Neukum says. 鈥淵ou take what you can get.鈥�