Sitting on the hill of an alien world millions of miles from home, a hardy NASA robot celebrates an anniversary today – one year on the planet Mars. The Mars rover Spirit has come a long way since it hurtled down through the planet’s atmosphere and came to a bouncy, airbag-protected stop at Gusev Crater on Jan. 3, 2004. It has survived more than four times its initial 90-day mission, driven miles across the Martian landscape and weathered a red planet winter only to scale hills for its human handlers