During its 90-day mission, Phoenix Mars is to excavate soil and ice as part of a study to learn whether the planet could have supported microbial life.
The landing on Monday signalled a triumph for Nasa, which has not had a successful powered landing since the twin Viking landers in 1976.
The last time Nasa tried was in 1999 when the Mars Polar lander suffered engine failure and crashed into the south pole.
Phoenix joins two other spacecraft on Mars' surface: the planetary rovers Spirit and Opportunity, which landed in 2004 and have been exploring opposite sides of the planet's plains.
Unlike the twin rovers, Phoenix is designed to stay in one spot and extend its long robotic arm to dig trenches in the soil.
It has an onboard laboratory to heat the soil and analyse the vapours for traces of organic compounds, an essential ingredient for life.