Step Five: Spirit enters the martian atmosphere
"Six Minutes of Terror"
About 20:29PST [04:29GMT], one of the most challenging aspects of the mission begins. In only six minutes, the spacecraft will slow down from 12,000 to 0 miles per hour.
The lander should come streaking in through the martian atmosphere, going about 12,000 miles per hour. Given atmospheric friction, the outside surface of the heat shield will be as hot as the surface of the sun (1,447 degrees Celsius, or 2,637 degrees Fahrenheit), but the rover will be protected by the heat shield and will stay at about room temperature inside the lander. The heat shield also aerodynamically acts as the first "brake" for the spacecraft, slowing Spirit down by thousands of miles per hour.

This is the equivalent to us driving at a speed of 100 MHP and coming to a complete stop in 3 seconds, only it goes on for 6 minutes.

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