Storm Chasing on the Red Planet
Combining a team of 20 scientists, a pickup truck and fast-forming dust tornadoes in the Arizona desert will help Mars' explorers harden their precious science instruments against violent Martian storms. Their daredevil experiment, called Project Matador, took place last summer to understand the dangers of much bigger dust storms expected during future Mars landing missions. The team is eventually preparing for Martian outposts where humans will work, live and more than likely have to frequently dust themselves off.
The chief Matador on the test project is Peter Smith of the University of Arizona, the scientist responsible for the Imager on the July 4, 1997, Mars Pathfinder camera -- the science package that snapped some of the most renowned and memorable photos ever taken of the Martian red-rust surface. Smith took the time to outline the goals and experimental plans for preparing for bad weather during future Mars missions.
Smith is keenly following the weather on Mars, as next year he will serve as co-investigator for Beagle 2, the lander part of the 2003 "Mars Express" mission, and Europe's first mission to the Red Planet. Beagle 2 science plans to probe for many key features of the planets potential astrobiology, including water, organic residues, and atmospheric samples.
But last summer, the consortia of intrepid storm chasers took their instrument-packed pickup to a previously plowed but unplanted farm in the Arizona desert, near Elroy in the Santa Cruz flats. Their tasks included defining the survivability of science packages for future Mars explorers.
A Devil of a Storm
The challenges to building and hardening an instrument on Earth -- testing it amid some of the more extreme conditions found inside an Earth storm -- just begins their modeling for how such a science experiment might fare hundreds of millions of miles away in the face of dusty tornadoes and lightning on Mars.
By comparison to how a dust devil in Arizona might stir up uncultivated farmland, the scale on Mars is much more daunting. Smith's camera's in fact had to survive just such an onslaught one stormy afternoon during the 83rd Martian day (or sol) back in 1997.
"At the Pathfinder site during its 83 sol mission, approximately thirty dust devils were either sensed by the pressure drop as they passed over the lander, or were imaged by the Pathfinder camera," says Smith. "Based on these observations, one might expect to see several dust devils per hour from an active site on Mars between 10 am and 3 pm. Few, if any dust devils will be present at other times. Dust devils typically form during late spring and summer and can be found at all latitudes. Exactly, how their population density varies around the planet is currently unknown."
The sheer geographical scope of a Martian storm can cover 100 times the size of an Earth dust devil. Martian tornadoes span up to 10 km (6 miles) high with a moving and circulating center nearly 10 football fields across (one kilometer, or six-tenths of a mile). But chasing such a storm on Mars is something any rover will likely need to steer clear from.
|Mars Orbital Camera (MOC) view of dust storm, a north polar dust storm observed on 29 August 2000 and a terrestrial dust storm on the same photographic scale, seen in a SeaWiFS image, acquired on 26 February 2000. This storm extends about 1800 km (1100 mi) off the coast of northwest Africa near the Earth's equator
Credit: NASA/JPL/Malin Space Science Systems
"Rovers and other robots must be carefully designed to withstand the sandblasting that they will endure from dust devils," says Smith as he looks for design specifications for Mars weather. "Bearing surfaces and solar panels must be protected and dust accumulation on solar panels will lower their efficiency."
Storm Chasing in a Flatbed Pickup
Calibrating a sensitive Martian explorer to efficiency-draining layers of dust requires some talented Earth drivers and a good air-conditioner to prepare for the sought-after grime. "Our mobile station is indeed a pickup truck," says Smith, "with computer data collection equipment inside the cabin (air conditioner on, as the outside temperature approaches 110 F). On the truck bed are wind velocity sensors, pressure sensors, thermometers, acoustical devices that listen to the particles striking the microphone, and field measuring devices.
But parking this science payload right in the path of an approaching tornado is exactly what the team trained for. "The truck is brought to a stop in front of the dust devil," said Smith, "and the engine turned off to reduce noise. As the dust devil passes overhead, all the listed parameters are measured as a team member films the event from close by. It is the synthesis of all these data that are analyzed to understand the interior workings of the dust devil."
High-voltage Martian Lightning
While the air pressure on Mars is approximately 100 times less than on Earth, the typically gentle winds strike chaotic pulses into the air when tons of statically-charged dust passes over a rover. Unpredictable lightning strikes remain one of the most challenging parts of dust-hardening a science payload for Mars landing.
|Vortical tracks left in the wake of a Martian dust devil in many tens of layers of several meters (yards) thickness in the walls of a mesa in southern Melas Chasma in Valles Marineris.
Credit: NASA/JPL/Malin Space Science Systems
Indeed, the Matador project measures changes in Earth's electric field that hover around 100 volts per meter but ramp up dramatically to 2,000 or 3,000 volts per meter during sudden static bursts.
While the pickup sports ruggedized laptops, such equivalent Martian discharges pose threats to sensitive electronics, or interfere with radio communications back to Earth. For human explorers, any habitat, greenhouse or space-suit must provide extra protection not only from the inevitable sand-blasting, but also the difficult to forecast lightning bolts.
"The spacesuits will quickly wear out as dust is ground into fabrics and joints," says Smith, "and dust will be tracked into the habitat. Once inside it will be recirculated throughout the various rooms where astronauts will breathe the dust until filters have removed it entirely. Any structures placed around the habitat must be dust devil hardened, for instance, greenhouses, which in calm weather would be made of super lightweight material."
Sweep to Compete
|Active Martian dust devil caught in the act of creating a sandblast track in Promethei Terra, December 11, 1999.
Credit: NASA/JPL/Malin Space Science Systems
To collect their calibration data, the Matador team members relied heavily on laser detectors, called LIDAR, which like RADAR, reflects from pressure and dust density changes inside a tornado to detail its inner workings. The laser has the principal advantage over RADAR of picking up the back scatter from much smaller particles and density changes than radio waves are capable of.
"Over a range of several kilometers LIDAR can not only locate and track dust devils, but also return their size and dust density. The "eye" of the dust devil is also commonly visible in the LIDAR scans. By sweeping the beam around the full horizon and plotting the return signals on a polar plot, there is a strong resemblence to World War II radar screens tracking approaching planes."
Among the early findings from last summer's storm chasing, the team has found the profiles of Mars and Earth dust devils may indeed prove to be a good test bed for future calibration studies. "We calculate that the dust devils will form and evolve in similar manners on Earth and Mars," says Smith, "driven by the solar heating of the surface and large scale convection. The electrical properties of Earth dust devils are poorly studied, but may be similar on Mars."
If sandblasting and Mars lightning pose a near-term threat, the longer term effects of rust and corrosion that give rise to the characteristic rust-red soil itself completes the triad of storm chaser study plans. Strapped to the pickup bed in Arizona is an instrument that will study corrosion directly, and is planned for future Mars missions. The package called MAOS, the Mars Atmospheric Oxidant Sensor, is a chemistry experiment to discover the source of oxidation (corrosion) on Mars. The flat grid panel of the sensor includes 384 electrical wafers, and as the films rust, the resistance to current flow measures weathering effects and rust.
Selected in December as part of NASA's contribution to the Beagle 2 mission to Mars next year, what got its early calibration on the back of a flatbed truck will soon perform its unique weather study from the rusty red surface amidst stormy dust devils.
Collaborators on the Matador project included Smith and others from the UA Lunar and Planetary Lab; John Marshall of NASA Ames Research Center, an expert on dust properties; William Farrell of NASA Goddard Space Flight Center, an expert on the electrical properties of dust devils; Greg DeLory of the University of California-Berkeley, who is managing the data system during the experiment; Allan Carswell of Optech, Ontario, Canada, who will operate the LIDAR; Barry Hillard of the NASA John Glenn Research Center, who will be using the electric field mill; Nilton Renno of the UA departments of atmospheric sciences and planetary sciences, an expert on Earth's dust devils; Michael Hecht and David Tratt of the Jet Propulsion Lab in Pasadena, CA and Dr. Aaron Zent from NASA Ames Research Center.
Related Web Pages
Beagle 2 Mars Mission
Mars Pathfinder Dust Devil Detections (GSFC Goddard NASA)
JPL Interview with Malin Space Systems on Dust Devil Images