The launch of Nasa's latest mission to Mars has been delayed by 24 hours.
Phoenix will study whether Mars could be habitable
The Phoenix spacecraft was to have launched on Friday, but lift-off has now been rescheduled.
Severe weather on Tuesday around the launch pad at Cape Canaveral, Florida, prevented engineers from fuelling the second stage of the rocket.
Phoenix will land on Mars' northern polar region to analyse samples of soil and ice and to search for signs of past and present life.
The probe has two launch opportunities on Saturday; one at 0526 EDT (1026 BST) and another at 0602 EDT (1102 BST).
The US space agency said that although fuelling of the Delta II rocket was expected to be complete by Wednesday morning, there was insufficient contingency time in the launch schedule to move forward with a Friday launch.
If everything goes to plan, Phoenix should arrive at Mars in May 2008.
It is due to carry out scientific operations for three months on the Martian surface. Phoenix will be stationary on Mars, in contrast to Nasa's roving robots Spirit and Opportunity.
Phoenix has a robotic arm that will dig down to the Martian ice layer and deliver samples to the lander's deck for analysis.
The mission is so-named because it carries with it the legacies of two earlier, failed attempts to explore Mars.
The lander was built for the Mars Surveyor mission originally planned for 2001, but mothballed by Nasa's administration in 2000. And many scientific instruments for Phoenix were built or designed for Mars Polar Lander which was lost as it entered the Martian atmosphere in 1999.