If successful, the probe will be the first lander to reach a Martian pole and the first to actually touch the planet's water ice. (Related gallery: "Phoenix Lander's Search for Mars Water" [August 3, 2007].)
What's more, it could settle the debate over whether Mars was once suitable for life.

As Phoenix closed in on the last miles of its journey, NASA scientists were gearing up for the "seven minutes of terror" that could make or break the U.S. $420-million mission. (Video: animation of the lander's expected turbulent touchdown.)

"Approximately 14 minutes before touchdown, the vehicle separates from its cruise stage," Barry Goldstein, Phoenix project manager at the Jet Propulsion Laboratory in California, said at a recent press conference.

"At this point we lose communication from the vehicle."

Once the craft reaches Mars's atmosphere, the next critical seven minutes make up what's known as the Entry, Descent, and Landing (EDL) phase.

Screaming down at about 12,600 miles (20,270 kilometers) an hour, the craft must open a parachute to slow itself for a three-minute glide to the surface about 70 miles (113 kilometers) below.

The craft's landing sequence then includes steps such as jettisoning its heat shield, extending its legs, and firing its landing thrusters.

"There are 26 pyrotechnic events, and each of those have to work perfectly for this to go as planned," Goldstein said. "Getting EDL communication [at touchdown]—that'll be the three seconds that I am really biting my nails over."

Risen From the Ashes

The tension for this mission seems especially intense, since Phoenix is not the first craft to attempt a landing at a Martian pole.