"It is concerning; this team has a very strong bond with the rover", said John Callas, the Opportunity project manager at Nasa's Jet Propulsion Laboratory. And that should help the solar-powered rover cope even though Mars' expanding dust storm has reduced its electricity-generating capability by more than an order of magnitude. Even in the worst of storms, only a layer of fine dust is left behind. "When the skies clear and the rover begins to power up, it should begin to communicate with us". However, the dust should warm the atmosphere and keep the rover above its minimum operating temperature. "The storm, which was first detected on May 30, now blankets 14 million square miles (35 million square kilometers) of Martian surface - a quarter of the planet". The storm is now about 10 billion acres in size, which is enough to cover North America and Russian Federation, or more than one-quarter of Mars.
Spirit finally went silent on March 22, 2010, stuck in deep sand and unable to favorably orient itself so its solar arrays could face the low-altitude sun during the harsh martian winter. Without them, there's a chance that Opportunity could drop below the temperature at which critical components would fail.
Opportunity was in remarkably good health going into the storm, with only an arthritic joint in its robotic arm, Mr Callas said.
It also showed the rover's temperature to be around -29C. "We're concerned, but we're hopeful that the storm will clear and the rover will begin to communicate with us", said Callas.
Callas said the dust storm had essentially turned day into night for Opportunity as the opacity of the atmosphere, a measure of how effectively the dust is blocking out sunlight, climbed to record levels.
Scientists who work with the rover get emotionally attached, Callas says. And, you know, the analogy I would use right now - it's like you have a loved one in a coma in the hospital.
"It just doesn't get any better than that".
"Having this dust storm occur under the visibility of the whole fleet of orbiters that we have, and eventually Curiosity participating in the research as well, is going to teach us a whole lot about how these storms behave", he added later in the briefing.
Opportunity would normally be able to generate over 600 watt-hours of energy per day with its panels at this time of the Martian year - which at its station is entering the northern hemisphere summer.
If the solar panels become caked with dust, and thus stop working properly, there won't be enough juice to restart the clock.
The Mars Opportunity rover has been on the Red Planet for well over a decade - it landed in 2004. Opportunity is in its 15th year; the team has operated the rover for more than 50 times longer than originally planned.
There is ample reason to believe Opportunity will indeed wake up, NASA officials said.
"We're all pulling for Opportunity", says Jim Watzin, the director of NASA's Mars Exploration Program. Opportunity, however, has kept exploring well past its expected mission lifetime.
That's helpful both for understanding the storms in general, and also for preparing for human trips to Mars.