The National Aeronautics and Space Administration said data received so far indicates Phoenix is running out of power each afternoon or evening, only reawakening after its solar arrays catch morning sunlight.

But scientists said the fraction of each day with the sun above the horizon is declining at Phoenix's arctic Martian landing site and dust raised by a storm last week continues to block some of the sunshine.

"This is exactly the scenario we expected for the mission's final phase, though the dust storm brought it a couple weeks sooner than we had hoped," said Phoenix Project Manager Barry Goldstein of NASA's Jet Propulsion Laboratory.

"We will be trying to gain some additional science during however many days we have left. Any day could be our last."

Phoenix landed on Mars May 25 for a planned three-month mission. It is now operating in its sixth month.