A dust storm on Mars is threatening NASA’s intrepid rover, Opportunity, but its human operators are hopeful that the 15-year-old robot will make it through. For now, Oppy, as it is fondly known, is asleep, waiting until it detects that it has enough power from its solar arrays to wake up and phone home.

During a media telecon today, John Callas, Opportunity Project Manager at the Jet Propulsion Laboratory (JPL), described the mood of Oppy’s human operators as feeling as one does when a family member is in a coma, but doctors are saying everything will be fine in time. They have a close “emotional connection” with the rover and thus are very concerned even though there are reasons for optimism.

The dust on Mars is very light and there is no concern that it will bury Oppy. Rich Zurek, Mars Program Office chief scientist at JPL, described it as being like talcum powder. Thrown up into the atmosphere, however, it increases opacity and prevents sunlight from reaching the solar panels that recharge the rover’s batteries.

Callas said right now it is “completely black on Mars, completely dark” because of this storm, which is expected to envelope the entire planet in the next few days. Although there have been planet-wide dust storms before, this one has already set a record of 10.8 tau, a unit representing the opacity of the atmosphere. That is almost twice the 5.5 tau opacity of the last major dust storm Opportunity experienced in 2007.

Consequently, sunlight cannot reach Oppy’s solar panels and the batteries are losing power. Callas said the power level dropped by more than a factor of two in just one day. He declared a spacecraft emergency, powering down all but the most vital spacecraft functions such as the master clock that tells the rover when to try to communicate back to Earth or open an eye to determine if battery power levels are rising.

The danger for Oppy is if the temperature drops too low for too long a period of time. The rover has eight small radioisotope heating units (RHUs) to provide warmth, but they are not enough to keep the rover warm indefinitely without any battery power.

The rover is at an “historic low energy level,” Callas said. The last transmission from the rover was on Sunday, June 10, at which time the power level was 22 watt hours compared to 645 watt hours just after the storm began on May 30.

Asked if there is any special concern about the batteries because of their age, Callas replied that despite 15 years and over 5,000 charge-discharge cycles, they still have 85 percent capacity. “They really are the finest batteries in the solar system. I only wish my cell phone battery had half of that.”

In other good news, he pointed out that the dust actually makes Mars warmer and summer is arriving at Oppy’s location, so the situation could improve. Callas said the rover is designed to operate as low as -55 degrees Celsius and the team currently expects temperatures will not drop below -36 degrees C. “We should be able to ride out this storm.”

As the size of the storm grows, it also is visible from NASA’s other operating Mars rover, Curiosity, located on the other side of the planet. Zurek showed these images from Curiosity taken three days (June 7 and June 10) apart to demonstrate how the visibility has changed.

Curiosity is nuclear-powered, so its power levels will not be affected by the storm. In fact, some scientists are excited about the chance to use Curiosity and the fleet of spacecraft in orbit around Mars to study this storm and learn more about how they form and evolve. That will be important not only for future robotic spacecraft, but potential human missions as well.

Callas’s overall message is that “we’re concerned, but we’re hopeful.”

Opportunity has already far exceeded its 90-day design lifetime. Opportunity and its twin sister, Spirit, were launched in 2003 and arrived at Mars in January 2004. Spirit operated for 6 years until it got stuck in sand and could not maneuver to keep its solar arrays pointed toward the Sun as winter arrived. Opportunity is still chugging along. Callas said that prior to the storm, the rover was in “remarkably good health” despite its age. “We’re eager for this storm to clear … and continue on with our exploration.”