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The Mars rover stays in the picture

Mars' reddish dust covers the Opportunity rover's solar panels in this downward-looking view, assembled from images taken by the NASA probe's panoramic camera from Dec. 21 to 24, 2011. The mosaic was put together in such a way as to omit the mast on which the camera is mounted.

One of the trickiest things that NASA's Opportunity rover does on Mars is take a look at itself — but for the six-wheeled rover, it's been a vital part of its eight-year-plus mission on the Red Planet.

This picture illustrates why the occasional once-over is so important: Because Opportunity relies on solar power, mission controllers back on Earth need to know how much dust is accumulating on the rover's solar panels. It's been a while since the dust has been swept off by Martian winds, and so there's quite a bit of dust covering the power-generating cells right now.

The dust hasn't been so much of a concern during the previous southern winters that Opportunity has spent in Meridiani Planum on the Red Planet. But as winter approaches this time, NASA has decided to position the rover on a north-facing slope so that it can soak up as much of the sun's weak rays as possible. That's a strategy that the rover team employed in the past with Opportunity's twin, the Spirit rover, which now lies moribund in Gusev Crater on the other side of the planet.

Opportunity is conducting research in place as it sits on the north-facing slope of a ridge known as Greeley Haven, on the rim of the 14-mile-wide Endeavour Crater. The rover's going to be there for a while: Mars' southern winter solstice takes place on March 30, and the planet's seasons last roughly twice as long as Earth's. So we'll be seeing a lot of the rover's surroundings at Greeley Haven — including the current focus of its scientific studies, a rock called Amboy.

For comparison's sake, here's a picture of Opportunity's relatively clean solar panels from September 2007:

NASA / JPL-Caltech / Cornell

This mosaic shows Opportunity's solar panels in September 2007 as seen by the rover's panoramic camera. The downward-looking view has been assembled to omit the mast on which the camera is mounted.

And here's a real treat from space artist Don Davis: A painstakingly assembled mosaic of imagery from Opportunity, looking east-southeast over Endeavour Crater to the far side just before sunset. You can see Opportunity's dust-covered solar panels and color-calibration sundial in the foreground. In the distance, you can see the long shadows cast on the crater floor — including the slight bump of a shadow that could well have been cast by Opportunity itself. It's a picture to marvel over, and astronomer/educator Stuart Atkinson does his fair share of marveling on the "Road to Endeavour" website. Emily Lakdawalla provides further details about Davis' rendition on the Planetary Society Blog.

Copyright Don Davis / NASA / JPL / Cornell

Don Davis created this mosaic from imagery sent back from Mars by NASA's Opportunity rover as the sun was setting on Jan. 27. The rover is looking out from a ridge toward the far rim of Endeavour Crater. The shadow of the ridge, and Opportunity itself, can be made out on the crater floor, toward the right edge of the image.

A little section of this picture served as this week's "Where in the Cosmos" picture puzzle on the Cosmic Log Facebook page earlier today. It didn't take long for Josh Jones to figure out what the picture showed, and to reward his mastery of a Martian mystery, I'm sending him a pair of 3-D glasses. Join the Cosmic Log Facebook community and stay tuned for the next "Where in the Cosmos" puzzle.

Speaking of Mars, my space-watching colleagues and I touched upon Red Planet research and other cosmic topics during the Weekly Space Hangout on Thursday. To wind up the week, here's the webcast, courtesy of Universe Today's Fraser Cain:

In this edition of the Weekly Space Hangout, we talk about the non-discovery of faster-than-light neutrinos, the possibility of quakes on Mars, and explanation for the ridge on Iapetus, the 25th anniversary of SN1987A, and a steamy water world.

More about Mars:

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.