At left, the sun appears blindingly bright but darkens as the dust storm intensifies.
The Opportunity rover was forced to halt operations last week as the storm swept over Perserverance Valley, bringing enough dust to blot out the sun. Tau is a measure of the atmosphere's opacity - that is, its lack of transparency.
Engineers are optimistic Opportunity will survive its trial by dust, but given its age and their emotional attachment to the hardy robot, they will not rest easy until skies clear enough for power levels to rise, allowing the rover to finally phones home.
Opportunity project manager John Callas told a press conference that NASA believes Opportunity will only drop to -36C and as such, "we think we can ride this out for a while". "And we're concerned about it, obviously".
"We have a very tight emotional connection with the rover; it's like having a loved one in a coma", he said. "And so we are".
"The current dust storm is providing an unprecedented chance to study Mars", Watzin said. Several days have passed and the storm still rages on.
That activity will involve returning to the science missions it's now been performing for 15 years. The rover was only created to last 90 days but has vastly exceeded expectation, and is now in its 14 year on the Martian surface.
Flight controllers tried to contact Opportunity, but the rover did not respond. For comparison, a major 2007 dust storm had an opacity level, or tau, above 5.5 while the current storm had an estimated tau of 10.8 as of 6 June. By now, two weeks later, the dust storm is nearly completely blotting out the Sun! "At this point, we're in a waiting mode".
Artist's concept of the Opportunity rover on Mars. And without that clock and sufficient power, it will never be able to signal Earth. But without the clock, some of these timers will wake it at night, and NASA won't know in advance when it will try to communicate.
The mission clock will trigger the computer to turn back on to check power levels sporadically, NASA said. In the middle of the chaos: the little Opportunity rover. The culprit? A dust storm blocked out a record amount of sunlight on the Martian surface, leaving the rover critically short of power.
If that cycle continues, the rover may eventually get too cold to operate, and things could get broken.
We are concerned but we are hopeful that the storm will clear and the rover will be able to communicate with us.
NASA launched two rovers - Opportunity and Spirit - in 2003 to explore the rocky surface.
Up until June 11, according to MER team member Keri Bean, Opportunity was still beeping back at NASA, to let them know that it was doing fine, despite the dust. It's also important to note that Opportunity has dealt with long-term storms before and emerged unscathed.
Spirit stopped functioning several years ago, while Opportunity has continued to deliver vital information about the planet.
It outlasted its 90-day initial mission by over 14 years, but a massive Martian dust storm could put an end to the solar-powered Opportunity rover's travels. While they can begin suddenly, they tend to last on the order of weeks or even months.