Meanwhile on Earth, the MER officials formed the winter planning team. “We do this every winter so that the science and engineering teams can formulate a strategy for the winter together,” said Herman.

Usually at one of these meetings, Herman presents predictions for the rover’s energy outlook. She makes recommendations for how many degrees the tilt of the rover and her solar arrays need to be in order to get enough energy to run the ‘bot’s internal survival heaters, and how much more of a tilt it will take for the rover to have enough energy to effectively conduct some scientific research and rove on.

With Herman’s tilt recommendations, the science team presents maps based on orbital imaging, mostly HiRISE images, and the tilt information to the rover planners (RPs). Together, they choose a slope that looks like it offers a good view of the surroundings and, ideally, some good targets within rover reach.

Once Opportunity emerged from conjunction and was back to sending home telemetry, Herman reviewed the data and worked to adjust some of the assumptions she had previously made in the power model. “The atmosphere was a little bit dustier than I was expecting,” she noted. “Unfortunately, that means less sunlight than I was expecting. Actually, the sky was the dustiest that Opportunity has ever seen this time of year. Based on that, I had to increase my assumptions and that lowered the power estimates.”

But these predictions are tricky and complicated and in the midst of her analysis, Herman also uncovered good news. When she looked at the dust model that keeps track of how much dust is on the rover’s solar arrays, it appeared that the arrays weren’t accumulating as much dust as she had anticipated, “possibly because the dust is stuck in the atmosphere,” she suggested. “It’s a bigger hit to your predicted energy to have dust on the panel than to have it in the sky. So in the end, my recently updated estimates predicted slightly more array energy,” she said.

Herman had previously recommended that Opportunity would need to park on 15-degree north-facing slopes to survive, but in August she changed her recommendation. “Ten-degree slopes appear now to be enough to survive winter,” she said. “Of course, a 15-degree tilt to the north would provide even more energy per sol.”

As for all that dust still lingering in the atmosphere?

The MER mission measures the dust in the sky with the Pancam, using near-daily images of the Sun to determine optical depth or what the team has forever referred to as Tau. “The measurement is influenced by dust accumulating on the camera itself, which can be mistaken for dust in the sky in any individual measurement,” said MER Science Team member Mark Lemmon, Associate Professor and atmospheric scientist at Texas A&M University. “Over time, the effects of the dust on the camera can be measured, and the calibration can be adjusted to improve the measurement of dust in the sky,” he said.

“Dust is slightly on the high side, maybe even back to normal in the last week or two,” Lemmon continued. “But that is a science result, based on a recalibration I've just done,” he explained.

Lemmon calibrates Pancam for taking the Tau and typically checks it three or four times a year. “Any seeming change has to stick around for a while before I believe it,” he said. “Now I have a change.”

Basically, he said, there has been a slow accumulation of dust on the Pancam optics. “It comes and goes. The calibration puts dust on the window (in a modeling sense), and takes it out of the sky. Without the calibration, dust on the window obscures light and is interpreted as dust in the sky.”