evidence: Do Flat Earthers Believe Other Planets Are Flat Too? Elon Musk Wonders [...] He’s referring to the fact that there’s a Flat Earth Society, for those who believe that the Earth is flat, rather than a sphere, but that there is no equivalent for Mars. The description of the Flat Earth Society on its website calls it, "A place for free thinkers and the intellectual exchange of ideas." [...] Update Wednesday, 2 p.m. EST: The Flat Earth Society responded to Musk's tweet on Tuesday evening and said that they do actually believe that Mars is round because "Mars has been observed to be round." The tweet then said they wish Musk has a "fantastic day."