On October 15, 1997 Cassini launched from Earth on its mammoth journey to the mysterious gas giant lurking at the edge of our solar system – Saturn. Now, almost 20 years later, it has all come to an end in dramatic, fiery fashion. Cassini began its final descent Friday into the dark heart of the solar system’s second biggest planet. At about 07:55 EDT (11:55 GMT) the probe dove into the planet’s...