Usually when we conceptualize religious competition, we think of local markets. Denominations export missionaries to foreign markets to proselytize, for example. This leads to competition in a local market, but two denominations competing in one local market may also compete with each other in a market in a different location. An example might be Seventh-day Adventists and Jehovah's Witnesses competing for converts in a town in Brazil and in a town in Cote d'Ivoire.
But can you imagine competing in different planets? Why not? Pope Francis has just stated that he would be willing to baptise aliens - even Martians. He said: "who are we to close the doors." See article here. Actually, this is not the first time that baptizing extra-terrestrial beings has been mentioned by a Pope. Pope Benedict XVI apparently once said that he would baptize an alien if the alien asked to be baptized.