There must be oxygen for breath, carbon dioxide and nitrogen for plants to make into food, sunlight to supply the energy for this all-important process. The temperature must not drop below the freezing point of water for too long a time, nor rise above a certain limit, which for most plants and animals is well short of the boiling point. These are not all the necessary conditions, but only a few of the outstanding ones. If a planet can not offer all the necessary conditions, it goes uninhabited. If even one of them is lacking, the planet is just as badly off as if it offered none at all.
Life is a very fussy tenant.
If we check over the list of planets with these considerations in mind, the outlook is not at all good for habitability of the houses in this part of the universe. The four outermost planets, Jupiter, Saturn, Uranus and Neptune, the giants of the solar system, are ruled out at once on several counts. For one thing, they are simply too big. The smallest of them, Uranus, has fifteen times the mass of the earth, while the largest, Jupiter, overtops us in weight of 318 times. The force of gravity on them of course is proportional to the mass, so that a man or any higher animal of the kinds we know would be crushed flat by his own weight if he landed on one of them.