Scientists are monitoring the build-up of a dust storm on Mars that could disrupt the operations of spacecraft and rovers.

Scientists are monitoring the build-up of a dust storm on Mars that could disrupt the operations of spacecraft and rovers.

The storm broke out last month in Hellas, the large impact basin that dominates the planet's southern hemisphere. It has since spread northwards and grown. Previous dust storms have ended up engulfing the whole planet for weeks at a time.

A large dust storm could affect all five exploration craft now orbiting Mars or working on its surface. They include the American space agency Nasa's two rovers, Spirit and Opportunity, the two Nasa orbiters, Mars Odyssey and Mars Reconnaissance Orbiter, and the European Space Agency's Mars Express orbiter.

Scientists are using a thermal imaging system on Mars Odyssey to watch the storm's progress.

Professor Philip Christensen, from the Mars Space Flight Facility in Arizona, who designed the orbiter's thermal imaging camera, said: "This storm is coming at a time in the Martian year - around the planet's closest approach to the Sun - when dust storms are common. But so far, this storm has not reached the severity of the big dust storms of 2001 or 2007."

In 2007, dust blocked more than 99% of the sunlight reaching both rovers.

He added: "If the dust causes a lot of obscuration, we lose the ability to image the ground. In big dust storms, the rover teams are strongly affected as dust in the air reduces sunlight which provides power for driving and science operations. And when the dust finally settles out, it coats the solar panels, diminishing their capability."

Dr Steve Ruff, a member of the rover team, said: "We've noticed increasing opacity over the last several days. This has produced roughly a 20% drop in power for Spirit.

"When dust kicks up, it hurts."