The "Impact to Egress" phase is when the probe made contact with the Mars surface.
Impact to Egress
Even after the landers and airbags safely bounce to a complete stop on Mars, the challenges of getting to Mars continue. It will take each rover a minimum of nine days to emerge from its lander cocoon, stand up, orient itself, safely unlock its body from the lander, and roll down to the martian ground. In this last episode of the Challenges of Getting to Mars video series, the rover team describes the Impact to Egress phase of getting six wheels on the surface.
From: Mars Exploration Rover Mission: Multimedia
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