I love a good conspiracy theory. And this story is inspiring some wild speculation.
A space plane that's been in Earth orbit for the last two years has just landed in California. It's unmanned and powered by solar energy. What exciting research has it been doing? No-one knows - except the US military - because it's classified.
It's been speculated, and strongly denied, that the space plane has been spying on China or conducting secret satellite research. But your guess is as good as mine.