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A new reading from the Phoenix Mars Lander is baffling researchers.

A successful measurement of the Martian soil on Thursday, the fourth of its kind, found the soil was bone-dry, despite the same probe's detection of humidity in the Martian air.

With both substantial amounts of water vapor detected in the atmosphere and water-ice discovered just inches below the surface, scientists would expect moisture to be found in surface soil as well. Yet readings an inch into the soil continue to turn up dry.

The probe on the Phoenix, which previously detected water vapor in the air, uses four needles, resembling a short fork. The speed at which heat and electricity moves between the needles tells scientists the amount of moisture present.

Measurements from the air have showed varying amounts of relative humidity, from close to 0 to nearly 100 percent.

Yet when the fork-like probe was stuck into the surface of the red planet, now on four separate occasions, it has measured no moisture.

"The soil isn't wet," said Peter Smith, the UA's chief scientist for the mission, "at least not enough for conductivity."

The sensors are much more sensitive, however, at measuring humidity in the air, Smith said. "We would need a fair amount of moisture to detect it in the soil."

Even when the air reaches nearly 100 percent humidity, because of the extremely low surface pressure and temperatures, compared to Earth, the moisture in Mars' air is one ten-thousandth of what we have in Tucson, Smith said.

Scientists are using the lander to search for moisture in the below-freezing soil, moisture that could potentially sustain life on the planet.

Humidity found in the air and ice found below the surface soil aren't the only evidences making the results of the soil samples seem contradictory.

Since the lander arrived on Mars, its robotic arm has been used to scoop up samples of Martian soil. When the soil was first collected, scientists observed clumping in the soil.

But as the soil was left in the scoop over time, the clumps began to weaken and crumble. Scientists believe these results also could point to evidence of moisture in the soil.

"The next step is to push the sensors down to the ice table," Smith said. "If there's a little melting on the surface of the ice, we'll find it."