These would be one of the biggest scientific discoveries in history.

Phoenix will be the first spacecraft to study the Martian arctic plains. Unlike NASA's mobile twin rovers, the lander will stay in one spot.

"We are ready to robotically operate our science lab in the Martian arctic and dig through the layers of history to the ice-rich soil below," said Phoenix Principal Investigator Peter Smith of the University of Arizona.

Phoenix is equipped to study the history of the water now frozen into the site's permafrost, to check for carbon-containing chemicals that are essential ingredients for life, and to monitor polar-region weather on Mars from a surface perspective for the first time.

Mars is a cold desert planet with no liquid water on its surface. But in the Martian arctic, water ice lurks just below ground level.

Discoveries made by the Mars Odyssey Orbiter in 2002 show large amount of subsurface water ice in the northern arctic plain. The Phoenix Lander targets this circumpolar region using a robotic arm to dig through the protective top soil layer to the water ice below and ultimately, to bring both soil and water ice to the Lander platform for scientific analysis.

According to NASA, the complement of the Phoenix spacecraft and its scientific instruments are ideally suited to uncover clues to the geologic history and biological potential of the Martian arctic.

Phoenix will be the first mission to return data from either polar region providing an important contribution to the overall Mars science strategy, "Follow the Water," and will be instrumental in achieving the four science goals of NASA's long-term Mars Exploration Program: determine whether life ever arose on Mars; characterize the climate of Mars; characterize the geology of Mars; and prepare for human exploration.

The Phoenix Mission has two objectives to support those goals, which are to study the history of water in the Martian arctic and search for evidence of a habitable zone and assess the biological potential of the ice-soil boundary.

Phoenix will assess the habitability of the Martian northern environment by using sophisticated chemical experiments to assess the soil's composition of life-giving elements such as carbon, nitrogen, phosphorus and hydrogen.

Identified by chemical analysis, Phoenix will also look at reduction-oxidation molecular pairs that may determine whether the potential chemical energy of the soil can sustain life, as well as other soil properties critical to determine habitability such as pH and saltiness.

The Phoenix landing would have happened 15 minutes earlier on Mars, but the radio signals take 15 minutes to travel from Mars to Earth at the distance currently separating the two planets.

If all goes as planned, the first pictures from Mars could arrive around 6:30 p.m. (0130 GMT on Monday), JPL scientists said.

(Xinhua News Agency May 26, 2008)