A planet can have a atmosphere that is sufficient for life, but of negligable mass compared to the core. In our solar system we have at least 2.5 examples of th

A planet can have a atmosphere that is sufficient for life, but of negligable mass compared to the core. In our solar system we have at least 2.5 examples of that: Earth, Venus and Mars. And that is not counting ocean moons with an ice crust such as Europa that might be hospitable to life as well.