Just like hurricane season or tornado season on Earth, Mars has stormy seasons, too. However, the Red Planet has dust storms, and they can be whoppers, which is bad news for the two Mars rovers, Spirit and Opportunity who rely on clear skies and sunshine for power. On April 21, Mars will be at the closest point to the sun in the planet’s 23-month, elliptical orbit. One month later, the planet’s equinox will mark the start of summer in Mars’ southern hemisphere. This atmospheric-warming combination makes the coming weeks the most likely time of the Martian year for dust storms, and given the current forecast based on data from the orbiting Mars Reconnaissance Orbiter and Mars Odyssey, these storms could be severe enough to minimize activities of the rovers.
There are several instruments on the orbiters that can monitor the weather patterns on Mars. The Mars Color Imager camera on Mars Reconnaissance Orbiter sees the entire planet every day at resolution comparable to weather satellites around Earth. Two other instruments — the Thermal Emission Imaging System on Mars Odyssey and the Mars Climate Sounder on Mars Reconnaissance Orbiter — monitor changes in airborne dust or dust-related temperatures in Mars’ upper atmosphere.
According to an article by Emily Lakdawalla at the Planetary Blog, the Climate Sounder is seeing temperatures in Mars southern hemisphere warm up rather dramatically, and even staying warmer than usual during the night. So far, however, the warming is staying south of the equator region where the rovers are.
The air has been relatively clear for several months on Mars, but in March increased haze reduced Spirit’s daily energy supply by about 20 percent and Opportunity’s by about 30 percent. Widespread haze resulted from a regional storm that made skies far south of the rovers very dusty. Conditions at the rovers’ sites remained much milder than the worst they have endured. In July 2007, nearly one Martian year ago, airborne dust blocked more than 99 percent of the direct sunlight at each rover’s site.
To supplement the orbiting assets looking down on Mars and the rovers, Spirit and Opportunity point cameras toward the sun to check the clarity of the atmosphere virtually every day. These measurements let the planning team estimate how much energy the rovers will have available on the following day.
“We can identify where dust is rising into the atmosphere and where it is moving from day to day,” said Michael Malin of Malin Space Science Systems, San Diego, principal investigator for Mars Color Imager. “Our historical baseline of observing Martian weather, including data from the Mars Global Surveyor mission from 1998 to 2007, helps us know what to expect. Weather on Mars is more repetitive from year to year than weather on Earth. Global dust events do not occur every Mars year, but if they do occur, they are at this time of year.”
Winds that can lift dust into the air can also blow dust off the rovers’ solar panels. Opportunity just benefited from a blast of wind the first week of April and Spirit got to minor cleanings in February. “We’re all hoping we’ll get another good cleaning,” said rover chief engineer Bill Nelson from JPL.
Unexplained computer reboots by Spirit in the past week are not related to dust’s effects on the rover’s power supply, but the dust-storm season remains a concern. Spirit received commands Tuesday to transmit more engineering data in coming days to aid in diagnosis of the reboots.
Well keep an eye on the spacecraft keeping an eye on Mars and provide updates during dust storm season on Mars.