Unlike Earth, Mars has no substantial atmosphere or global magnetic field, and so is completely unprotected against the flood of energetic radiation particles from outer space. (sciencedaily.com)
And, as an added bonus, the planet appears relatively broad for its mass, indicating the presence of a substantial atmosphere. (scientificamerican.com)
Titan is the only moon in the solar system with a substantial atmosphere and the only place besides Earth with a weather cycle we can study. (discovermagazine.com)