NOTE: A technical issue prevented video of Opportunity from playing during the segment, which is why the Phobos graphic is displayed on screen in the video above the entire time.
Two unmanned probes sent to study the Red Planet were launched on different years on this day and history and had vastly different levels of success.
The Soviet Phobos 1 probe was launched on July 7th, 1988. Its mission was to study Mars, and as its name indicates, the largest Martian moon, Phobos. The launch was successful, but as the probe was en route to Mars, a computer error caused contact to be lost with the probe. The sister probe of Phobos 1, Phobos 2, did make it to Mars and returned some data and pictures, but another error with that probe caused contact to be lost before the mission was completed.
On July 7th, 2003, the NASA Mars Opportunity Rover was launched. It would land on Mars in January of 2004. Like its sister rover, Spirit, NASA planned for Opportunity to work for just over 90 days, but this rover is still operational as of July 2014! The rover has traveled nearly 25 miles. It has studied a large crater, a martian meteorite and even its own heat shield along its travels. It has also returned over 180 thousand photographs of Mars.