At 125 km (78 miles) above the surface, Phoenix will enter the thin martian atmosphere. It will slow itself down by using friction. A heat shield will protect the lander from the extreme temperatures generated during entry. Antennas located on the back of the shell which encases the lander will be used to communicate with one of three spacecraft currently orbiting Mars. These orbiters will then relay signals and landing info to Earth.
Phoenix streaks through the martian atmosphere protected by its heat shield as it uses friction to decrease its velocity. (Image Credit: Phoenix Mission, University of Arizona)
After the lander has decelerated to Mach 1.7 (1.7 times the speed of sound), the parachute is deployed. Shortly after the parachute is deployed, the heat shield is jettisoned, the landing radar is activated, and the lander legs are extended. The lander continues through the Martian atmosphere until it comes within 1 km (.6 miles) of the Martian surface. At this point, the lander separates itself from the parachute. It then throttles up its landing thrusters and decelerates.
The lander glides towards Mars just after its parachute is deployed. (Image Credit: Phoenix Mission, University of Arizona)
When Phoenix is either at an altitude of 12 m (39 ft) or traveling at 2.4 m/s (7.9 ft/s), the spacecraft begins traveling at a constant velocity. The landing engines are turned off when sensors located on the footpads of the lander detect touchdown.