Sen— NASA's surviving Mars rover Opportunity notched up a remarkable record today when it began its 3,000th martian day, or sol, on the Red Planet.

The robotic runabout, which bounced to a landing on Mars way back in January 2004, along with sister Mars Exploration Rover (MER), Spirit, was designed for an original mission lasting 90 Earth days.

Spirit became trapped in sand in November 2009 after two of its six wheels stopped working. Power ran out and nothing has been heard from it since March 2010, ending an amazing marathon of its own.

But Opportunity, now near the rim of Endeavour Crater, has kept on trucking for 33 times the original target, producing a wealth of interesting discoveries and other data.

Astronomy populariser Stuart Atkinson has kept a fascinating blog, The Road To Endeavour, which has kept track of Opportunity's adventures - or Oppy as he calls it. Here he tells Sen why its mission has been so important.

"I think the greatest significance of the whole MER mission is the way it's transformed Mars into a real, physical place we can now finally imagine walking on, hiking across and exploring in person on foot. Oppy has crossed deserts, gone down into craters, climbed up ledges, studying rocks and dirt and dust - essentially doing everything a human geologist would do, except stop for a swig of water and a choccie biscuit now and again - and everytime she's reached a new horizon she's shown us something new, something amazing. She's allowed us to go on a trek across Mars, with a relentlessly changing view, and that's fantastic!

"Also, she's giving us a very human view. All previous missions had cameras that were pretty "low down", meaning we had either a badger's or a Shetland pony's view of Mars. But the rovers have cameras as high above the surface as our eyes would be if we went to Mars, so looking at the pictures sent back by Oppy is really like being there. Put together a hundred or so Opportunity images in a gif animation and it's like walking alongside her, seeing the terrain rise and fall, going past rocks and boulders. We've never had that before.

"And she's shown us such amazing sights! I remember when she set off across the great dust ripple sea of the Meridiani desert, heading for Victoria. The desert looked like something from a Dune novel, just mile after mile of dunes, all the way to the horizon, Arrakis made real. I half expected a sandworm to rear up out of the dust and devour Oppy, after she sent back one last pic showing a huge mouth opening up in front of her! Then when she pulled up to the edge of Victoria Crater and peered over the side, the view was simply breathtaking - the huge bowl floor of the crater, surrounded by crumbling cliffs and great towers of layered stone, all beneath that cathedral dome orange-pink sky, just stunning.

"Then she set off for Endeavour, on that surely-impossible three-year drive, and being honest I think very few of even the most optimistic rover huggers dared to believe she'd make it. But she proved us all wrong, and drove up onto Cape York in triumph, straight to Odyssey Crater, with its dozens of boulders and stones scattered all around it, and it felt like a whole new mission, like Opportunity had just landed. Now she's reached the northern tip of the Cape, and is preparing to head south again, go back the way she came, before going mountain climbing up Cape Tribulation. She'll make it to the top, I'm sure, then she'll look down on the crater and see the most incredible view... I can't wait.

"And this is why it's so exciting - we're walking beside Oppy every step of the way, because the images she takes are put on the web within hours of them being taken. That was a conscious decision on the part of the MER team. Rather than hoard their images and grudgingly release a few every now and again, like some missions have (and still do, sadly) they decided they wanted everyone to feel a part of the adventure so arranged for the images to be on the web as soon as possible.

NASA's Mars Rover Opportunity catches its own late-afternoon shadow by Endeavour Crater. Credit: NASA/JPL-Caltech/Cornell/Arizona State Univ.

"This has been fantastic. It's as if Columbus was sending back daily updates from the New World, or Drake and Magellan were blogging and Tweeting during their voyages of discovery. People all around the world - in school computer rooms, bedrooms, offices, wherever - can go online and see pictures taken on Mars just hours earlier, for free! Not only that, but we're actually encouraged by the MER team to use them to make mosaics, panoramas, 3D views and more. It's made a lot of people genuinely feel a part of the mission.

"But why is this mission so personal to me? Why has it inspired me to write my blog, short stories and poetry? Because I can't help thinking that it's my "Apollo". I was too young to enjoy the Apollo missions. I was aware they were going on, but didn't really 'get' them. With MER, I had the anticipation of the build-up to launch, then the drama of the landing, and since then one 'new mission' after another as Oppy has driven up to, and explored, one new site after another.

"The MER mission has been more like a series of missions, each one touching down at and exploring a different site - just like Apollo. And seeing as there's now a pretty good chance I won't get to see manned missions to Mars in my lifetime, because our politicians are too short-sighted and timid and afraid of glory, and would rather spend billions on pointless foreign wars and bailing out criminally foolhardy banks, Spirit and Oppy were my martian Neil Armstrong and Buzz Aldrin."