NASA remembers July 4 Mars milestone that made its rovers possible

NASA is remembering one of its most notable July 4th events: the arrival of its Sojourner on Mars in 1997. Depending on your age, you may not be familiar with Sojourner, having instead learned about Curiosity, the now-defunct Opportunity, and perhaps even the Spirit rover, which was active on the Red Planet from 2004 to 2010. Lesser known is the …