NASA said that its Phoenix spacecraft is on track for its destination in the Martian arctic. The NASA officials noted that the spacecraft is in fine health and the latest calculations have shown that Phoenix is currently heading to an area that is less than eight miles from the center of the initial target area.

"All systems are nominal and stable," said Ed Sedivy, Phoenix spacecraft program manager for Lockheed Martin Space Systems, Denver, which built the spacecraft. "We have plenty of propellant, the temperatures look good and the batteries are fully charged."

On Sunday, shortly after the annual 500-mile race at the Indianapolis Motor Speedway, Phoenix will be approaching Mars at about 12,750 miles per hour, a speed that could cover 500 miles in 2 minutes and 22 seconds.

The mission was launched on August 4, 2007 from Cape Canaveral Air Force Station in Florida, with a landing site established at 68 degrees north latitude, 233 degrees east longitude, in Vastitas Borealis, or Mars’ arctic plains. The primary mission will be of 90 Martian days (the equivalent of 92 Earth days) at temperatures of minus 73 C to minus 33 C (minus 100 F to minus 28 F).

"We may decide on Saturday that we don't need to use our final opportunity for fine tuning the trajectory Phoenix is on. Either way, we will continue to monitor the trajectory throughout Saturday night, on the off chance we need to execute our contingency maneuver eight hours before entry," said Barry Goldstein, Phoenix project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.

Phoenix’s arrival on Mars will be one of the critical points of the mission, because it’s the first time when NASA attempts to land a spacecraft on Mars at such a high northern latitude. Several factors could adversely affect the landing. High winds could make landing much more difficult. High landing speeds or too much tilt at landing will also risk damage to the spacecraft.

The earliest possible time when mission controllers could get confirmation from Phoenix indicating it has survived landing will be at 4:53 p.m. Pacific Time on Sunday (7:53 p.m. Eastern Time). Of 11 previous attempts that various nations have made to land spacecraft on Mars, only five have succeeded.

The mission will seek to answer questions about that part of Mars and help resolve broader questions about the planet. The key questions Phoenix will address concern water and conditions that could support life.

The Phoenix landing region has water ice in soil close to the surface, which NASA’s Mars Odyssey orbiter discovered for much of the high-latitude terrain in both the north and south hemispheres of Mars.

Phoenix will dig down to the icy layer. It will examine soil in place at the surface, at the icy layer and in between. It will scoop up samples for analysis by its onboard instruments. One key instrument will check for water and carbon-containing compounds by heating soil samples in tiny ovens and examining the vapors that are given off. Another will test soil samples by adding water and analyzing the dissolution products.

Cameras and microscopes will provide information on scales spanning eight powers of 10, from features that could fit by the hundreds into the period at the end of this sentence to a survey of the landscape by a mast-mounted camera. A weather station will provide information about atmospheric processes in an arctic region where a coating of carbon-dioxide ice comes and goes with the seasons.

"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, Tucson.