LOS ANGELES — NASA on Monday declared an end to the Phoenix mission, some five months after the spacecraft became the first to land in Mars' arctic plains and taste water on another planet.

Mission engineers have not heard from the Phoenix lander in over a week. It fell silent shortly after a raging dust storm blocked sunlight from reaching its solar panels. Although ground controllers will direct two satellites orbiting Mars to listen for Phoenix for several more weeks, the chances that it will respond are slim.

"We are actually ceasing operations, declaring an end of mission operations at this point," said project manager Barry Goldstein of NASA's Jet Propulsion Laboratory, which managed the $475 million mission.

Phoenix's demise was predicted. Unlike its hardy twin rover cousins Spirit and Opportunity, which are approaching their fifth year near the red planet's more hospitable equatorial region, Phoenix's days were numbered from the outset. With sunlight waning and winter encroaching, scientists had said it was a matter of time before Phoenix would freeze to death.

Doug McCuistion, who heads the Mars exploration program at NASA headquarters, said people should view Phoenix's end as "an Irish wake rather than a funeral."

Since its successful landing in May, Phoenix has sent back a bonanza of scientific discoveries. Its first breakthrough was the confirmation of ice at its landing site. Previous measurements from space suggested there was frozen water lurking inches below the surface, but Phoenix became the first robotic probe to touch and taste it by melting icy soil in one of its lab instruments.

The Phoenix mission was not trouble-free. Early on, Phoenix was dogged with technical difficulties involving its tiny test ovens designed to sniff for traces of organic, or carbon-based compounds. Several oven doors failed to open all the way; the lander also had trouble getting the dirt into the ovens and a short circuit threatened to render the instrument useless.

Originally pegged to last three months, Phoenix lasted a little over five months, flexing its long arm to dig trenches in the soil and delivering dirt and ice to its onboard instruments to analyze.

By the end of its prime mission, Phoenix determined the soil was slightly alkaline, detected falling snow and found minerals that suggest the ice may have melted at some point, although the soil is currently bone-dry.

Phoenix grew considerably weak in recent weeks as the Martian weather deteriorated. It braved plunging surface temperatures and a swirling dust storm that drained its power. It last communicated with Earth on Nov. 2.

Scientists tried to look on the bright side.

"It's always a sad situation to not be able to communicate with it, but it lived beyond its warranty," said mission scientist Ray Arvidson of Washington University in St. Louis.

Despite overcoming the oven troubles, Phoenix has yet to discover the elusive organic-based compounds essential for simple life forms to emerge. So whether the Phoenix landing site was habitable remains an open question.

The mission's chief scientist, Peter Smith of the University of Arizona in Tucson, said the team will focus on analyzing the science results.

"I'm still holding out hope," Smith said.