(a) Mercury is not inhabitable due to the following reasons:
1. A part of it turned towards the Sun is always in sunlight. There it is a continuous long day. The temperature reaches 450°C in this hottest part. It experiences a perpetual summer.
2. Its other side is always turned away from the Sun. There is a continuous night on this side. It is like perpetual winter, the temperature going 150°C below freezing point. Therefore, the diurnal range of temperature is very high.
3. There’is very little atmosphere and no .water on this planet. The atmospheric envelope is so thin that Mercury’s world is airless.
(b) Venus is not inhabitable because its atmosphere contains 96% of carbon dioxide and the temperature reaches the maximum of 480°C. It is the hottest planet in the solar-system.
(c) Jupiter is not inhabitable due to the following reason :
1. Its surface temperature is very low (-148°C)
2. It has no water and there are tremendous storms on the surface of the Jupiter.
3. The atmosphere of the Jupiter is unbreathable, because of absence of oxygen and presence of poisonous gases like ammonia, methane and ethane etc.
(d) Neptune is not inhabitable because of very low surface temperature (-216°C) and mgthane clouds surrounding it.
(e) Saturn : Saturn is the second largest planet in solar system. The planet itself is mostly made up of light gases and it is less dense than water. If Saturn were placed in a large ocean, it will float on water Scientists, however believe that the planet may have a solid core.