Seems that humans aren't the only ones to suffer ailments like stiff shoulders, easily broken limbs and dimming eyesight as they get older.

As winter descends upon Mars' Southern Hemisphere, NASA's rovers appear to be entering the winter of their lives as well, suffering from problems stemming from aging hardware. Nonetheless, they're continuing to make new discoveries about the Red Planet.

Spirit, stationed about 15° south of Mars' equator (roughly equivalent to northern Brazil and central Africa on Earth), is starting to slow down because it's receiving less sunlight. Opportunity is closer to the equator, so experiences less seasonal variation in light. Despite the age-related problems they are expecting, they have performed beyond all expectations; they were originally designed to operate for just 90 days when they landed on opposite sides of Mars two and a half years ago.

Spirit's right front wheel gave up the ghost back in March. The rover team decided  to park Spirit on a rocky slope called Low Ridge Haven for the winter. From this spot, Spirit has continued to examine the rocks and soil around it while measuring the atmosphere's temperature.

Opportunity, like some of us, is suffering from a a stiff shoulder joint - in this case, on its instrument deployment arm. The rover team is trying to avoid exacerbating the problem, using the arm as little as possible. Its anemic performance was a few weeks ago, however, when the wind blew the dust off of its solar panels, allowing them to absorb more solar energy.

Over the past weekend, Opportunity examined a 30-metre-wide crater named Beagle, and is now on its way to an area where the wind has deposited sand and dust in rippled structures. The presence of sand clods indicate the possibility of small amounts of water, according to rover team member Ray Arvidson of Washington University in St Louis, Missouri.

Arvidson hopes the site will reveal something of the area's history geologic history over the past four billion years, when several small lakes apparently dried up. He'd like to know how acidic the water was farther back in time on the Red Planet. "That really tells you about habitability," he says. "Most astrobiologists think that life is easier to get started in more neutral conditions." Earlier geologic data indicates that Martian water was very acidic.

In the meantime, click on the picture below to get a better look at a recent image of the Martian surface.