The Smithsonian is celebrating 10 years of operations for the Spirit and Opportunity Mars probes with a gallery of their best work

SPIRIT and Opportunity were supposed to explore Mars for just 90 days. Ten years on, Opportunity still knocks. Here's some of our favourite snaps from their epic voyage.

ROVER MARS .. A Martian sunset, captured over the rim of Gusev Crater by the Spirit Rover

MARS. The Red Planet. Rovers Spirit and Opportunity Rovers have now been rolling over its surface for 10 years. Here's some of their favourite snaps.

Few sights in the night sky have inspired as many poems, songs, prophecies and stories. For the past 40 years, particularly the past 10, we've green getting an up-close and personal insight of the fourth planet's moods and mysteries.

The two-rover missions launched in 2003 were slated to last 90 days: 3650 days later, one is still awake and exploring.

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"Spirit and Opportunity: 10 Years Roving Across Mars" is a special presentation at the Smithsonian's National Air and Space Museum where 50 of the best photographs from the two rovers have been presented as an art exhibit.

It includes many large-scale photographs of craters, hills, dunes, dust clouds, meteorites, rock formations and the Martian sunset.

A Martian sunset, captured over the rim of Gusev Crater by the Spirit Rover. Picture: NASA

John Grant, a planetary geologist at the museum who is part of the rover mission team, organised the exhibit, in part as a travel log with images on one side from Sprit and images from Opportunity on the other. The rovers landed in January 2004 on opposite sides of Mars and began exploring volcanic deposits and plains, as well as meteorites and impact craters, so the exhibit also focuses on the science, Grant said.

"Every one of the images you see here tells a story of discovery that goes along with the story of beauty on Mars," Grant said.

It's a look at an alien planet through the rovers' eyes, he said.

Uncovering signs of the past presence of water and a more habitable environment are among the rovers' most important discoveries. Some were made by accident.

After about 800 days, one of Spirit's front wheels stalled and stopped functioning. So the engineering team decided to continue driving it in reverse, dragging the broken wheel across the Martian surface. That dragging dug a trench behind the rover that soon uncovered a new material as white as snow. It turned out to be silica material that would normally be found in hot springs and hydrothermal systems - habitable environments.

"It was a total surprise," said Steven Squyres, an astronomy professor at Cornell University who headed the Mars Exploration Rover mission. "It was just pure good luck. We wouldn't have even seen that if we didn't have the busted wheel."

NASA's Mars Rover Opportunity catches its own late-afternoon shadow in this dramatically lit view eastwards across Endeavour Crater on Mars. (Photo by: Universal History Archive/UIG)

The rovers also found concretions and layered sedimentary rocks made of sulfate salt that showed water had once been on the planet's surface.

While some panoramic images clearly show the red Martian landscape, other images focus on other colours that can be found in Mars' rocks, soil and sky. One image of the Martian sunset shows a bluish colour in the sky, which is usually pink in the daytime due to the reddish dust in the atmosphere. But it turns blue at sunset - the opposite of Earth, Squyres said.

Jim Green, NASA's director of planetary science, said the rovers have made huge strides in learning about Mars to eventually send humans there. Another rover called Curiosity is also now exploring the surface, and NASA plans to send more rovers before humans.

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