A comet first spotted by a Ukrainian amateur astronomer looks to be just the second known object to visit our cosmic neighborhood from beyond the solar system. What could be an even bigger deal is that this one was discovered as it's still approaching us. The comet was found by Gennady Borisov of Crimea on Aug. 30, and went by the temporary name GB00234 until very recently. After being watched by several other observatories over the past few weeks, it was given the official name of C/2019 Q4 (Borisov) by the Minor Planet Center on Wednesday. It appeared to follow...