London, September 10 : NASA's Phoenix Mars Lander has abandoned its underground salt search, as soil from the Lander's deepest trench has failed to fall into its wet chemistry laboratory, and mission managers are abandoning any further attempts to study the soil - at least for now.
According to a report in New Scientist, the soil comes from a trench called 'Stone Soup', which reaches some 18 centimeters below the surface - much deeper than any other trench the lander has dug.
Stone Soup sits between two polygons, raised hillocks that are similar to permafrost features on Earth.
If liquid water was once present at the landing site, it might carry salts, like perchlorate, down between the polygons.
Researchers had hoped to compare salt concentrations at the bottom of the trench to those closer to the Martian surface, which could help reveal the history of any liquid water present in the area.
"This was what we were hoping would be the different and interesting sample," said wet chemistry lead scientist Sam Kounaves of Tufts University in Medford, Massachusetts.
Phoenix has attempted to deliver soil from the trench twice to its wet chemistry lab, which is part of the onboard MECA (Microscopy, Electrochemistry, and Conductivity Analyzer) instrument.
The team aimed to place the soil in one of two remaining wet chemistry cells, which can detect the presence of dissolved salts. But, both soil samples seemed to be too sticky to fall past a screen on the device.
The second attempt, which took place on September 7, left a large pile of soil on the instrument. The sides of the soil looked impressively vertical, attesting to the sample's stickiness.
"Mars is presenting us with a material that's more cohesive than most people had thought," Kounaves told New Scientist. "This cohesiveness might be due to clays, salts, or some sort of electric charge," he added.
Now, the wet chemistry lab will analyze more soil from a trench called Snow White, which it has studied before. That will be used to confirm previous measurements.
According to Kounaves, if time permits, the team may also use the Lander's robotic arm to turn over one of the rocks on the landing site and look for visual evidence of salt deposits.