Is it possible that an ancient Martian civilization has something to do with this cross?
Certainly, Mars is currently dry and barren, yet NASA administrator Charles Bolden affirms that life existed on the planet and may still do so. Ancient microtechnology could explain the advanced world that far superseded our own.
Even prior to the arrival of Christianity, the Celtic cross was widely used by ancient people. Its sides denoted the elements of nature, the four directions of the world, and the sides of light. The circle above the cross also had many explanations ranging from sun worship to the fact that the symbol appears aesthetically more pleasing.