I've actually listened to some of the tech talk on this ovr the last couple of days. Apparently the atmosphere on Mars is thinner than at St. James Park on a Saturday so the time it takes to slow down is much longer than on Earth. The thing would be travelling at around 6 times the speed of a bullet when it went into the entry phase so they were not sure if it would slow enough to land rather than belly flop at great speed on the surface. They had to get it from the above sped to a jogging pace in 7 minutes. No pressure then. I think it all sounds quite marvelous really for somebody who used to listen to "Journey into Space" as an 8 year old on the wireless.