Factbox: One year on, MH370 theories abound

SYDNEY (Reuters) - Speculation about what happened to Malaysia Airlines Flight MH370 ranges from sober, science-based arguments to outlandish conspiracy theories. Here are some of the most prominent: CRASHED IN SOUTHERN INDIAN OCEAN Official investigators used analysis from British firm Inmarsat of "pings" to its satellite from MH370, combined with data direct from the plane before it stopped transmissions, to conclude the plane had flown south after it dropped off Malaysian military radar and crashed in the southern Indian Ocean. The well-respected Independent Group (IG) has done its own analysis and believes the plane is probably near the current search zone, but not necessarily within it. Just why MH370 ended up there is contested both within IG and others who support the official findings. Some plump for a hijack scenario, others point to technical or pilot error. A British captain, Simon Hardy, says the plane did a fly-by of the pilot's home island of Penang before flying repeatedly in and out of Malaysia and Thailand to confuse air traffic controllers. IT WAS ACCIDENTALLY SHOT DOWN This theory was the thrust of the first book published on the incident, 'Flight MH370 The Mystery'. London-based author Nigel Cawthorne said the plane may have been accidentally shot down during joint U.S.-Thai military exercises in the South China Sea. Such accidents have happened before: Korean Air flight 007 was shot down by the Soviet Union in 1983, and the U.S. Navy downed an Iranian airliner in 1988. Aviation experts are skeptical about a U.S. and Thai cover-up, proponents argue the very nature of a "cover-up" is that it is hard to disprove. IT WAS BROUGHT DOWN NEAR DIEGO GARCIA The former head of France's Proteus Airlines, Mac Dugain, put forward the theory that the plane may have been shot down by the U.S. military, fearing a Sept. 11 style attack on the U.S. Navy base on the remote Indian Ocean island of Diego Garcia. Dugain pointed to the testimony of residents in the Maldives who reported seeing an airliner traveling towards the island, although their claims were widely dismissed. IT IS IN RUSSIA Former pilot and regular CNN aviation expert Jeff Wise speculates that MH370 flew north along national borders to avoid radar before landing in Kazakhstan as part of a Russian-engineered plot. Wise's theory is dependent on somebody on board the plane tampering with key satellite transmission data to give the impression it flew south. He noted the relevant instruments could be accessed by a panel in the cabin and that there were three Russians on board. Wise acknowledges he can offer no motive to explain why Russia would want to steal a Malaysian jetliner. IT IS IN PAKISTAN FOR USE IN TERRORISM A retired U.S. lieutenant general spread the theory the plane was flown to Taliban-controlled Pakistan, to be used to carry weapons of mass destruction for an attack on Israel. The idea was given a boost by newspaper mogul Rupert Murdoch, who tweeted: "Maybe no crash but stolen, effectively hidden, perhaps in Pakistan, like Bin Laden". MH370 and MH17 WERE SAME PLANE This theory is based on photos of the MH17 crash site in Ukraine, which proponents argue shows that the second crashed plane was in fact MH370, a later 777 model that had some small changes to its body. How MH370 could have been hidden for six months before being substituted for MH17 - and what happened to the bodies - is not explained. IT WAS ABDUCTED BY ALIENS Self explanatory. (Reporting By Jane Wardell; Editing by Alex Richardson)