A cannon-launched contraption made of wire, wood and PVC pipe could ramp up the search for water on Mars.
The inauspicious prototype for the device, called the Mars Time Domain Electromagnetic Sounder, is a long wire loop that lies flat on the ground and creates a changing magnetic field. That field triggers electrical currents that flow deep underground and shift in response to features they pass through, such as bedrock or liquid water.
A consortium of scientists is testing the gadget, which could be launched from a lander or rover to peer below the Martian surface — through solid rock — and see deeper than any subsurface radar to date. The currents generated by the device create their own magnetic fields that the wire at the surface can detect and use to paint a picture of what lies beneath.
"We think there are small amounts of water in there," Robert Grimm, the project's principal investigator at the Southwest Research Institute in Colorado told SPACE.com. "What the biologists want to find is some kind of aquifer, a sponge of moisture at a certain depth — a depth where Mars' own geothermal heat can sustain liquid water."
Grimm's paper research the device is detailed in the online May 15 edition of the journal Planetary and Space Science.
Shoot 'em up
The loop envisioned for Mars would consist of about 656 feet (200 meters) of copper wire. The device's masterminds tossed around several ideas for how earthbound engineers could unspool and arrange the wire in the dust of Mars. They could trawl it out behind a rover that rolls in a wide circle, they thought, but in the interest of ease, not to mention dramatic flare, they decided to shoot it out. A compressed gas cannon fires projectiles that rapidly uncoil the wire behind them in flight.
Now the wire is launched from a PVC pipe tacked on to an off-the-shelf pressurized air tank, but if it is ever sees Martian soil, the launch tubes will likely be aluminum, Grimm said.
"The main challenge was getting the spooling right," said Robert Warden, a mechanical engineer at Ball Aerospace and Technologies Corp., which built the deployment system. The spools had to be compact but pay out quickly at nearly 70 mph (112 kph).
From the test launches the scientists determined that a similar device built for a Mars mission would weigh less than 13 pounds (6 kg) and could detect groundwater as deep as 3 miles (5 km) beneath the Martian crust.
The device measures how anything below the surface conducts electricity. It could detect conductivity in the soil, bedrock, metals and groundwater. Such devices, minus the launchers, are already used for underground exploration here on Earth. They are called inductive systems.
"The whole idea of using induction is still frankly a little bit novel to the space science community, they haven't seen anything like this since Apollo," Grimm said. Apollo astronauts used magnetometers to make lunar induction measurements during NASA's manned moon missions between, according to NASA records.
The launched-wire device generates electricity to detect magnetic fields in a manner similar to another version of such devices on Earth that passively detect the planet's natural electromagnetic energy underground. Grimm is building a new water detector for Mars that would use the same principle. Since it would not need to generate electricity it would be more compact. There is one hitch, though.
"The big question on Mars is to know if that energy is there. We have to go there to measure it to see if we can use it," Grimm said.
NASA has no plans to use the induction systems now, but if it were to deploy one, it would likely fly out on a rover, Grimm said. Or it could be designed to crash-land from a Mars orbit, the blow softened by air bags, for example, he says.
"It just comes down to the 'who cares factor,'" he says. "If people want to find out if there's some kind of water locked deep down then they'll have to go with the induction method."