(CNN) -- It's a mystery that authorities still haven't been able to solve: Where is Malaysia Airlines Flight 370?
There were still more questions than answers Thursday as U.S. officials said investigators will start combing the Indian Ocean as they look for the missing aircraft.
Why would authorities expand their search rather than narrowing it?
New information, U.S. officials told CNN, indicates the missing airplane could have flown for several hours beyond the last transponder reading.
Malaysian authorities believe they have several "pings" from the airliner's service data system, known as ACARS, transmitted to satellites in the four to five hours after the last transponder signal, suggesting the plane flew to the Indian Ocean, a senior U.S. official told CNN. That information combined with known radar data and knowledge of fuel range leads officials to believe the plane may have made it to that ocean, which is in the opposite direction of the plane's original route.