Can Neptune sustain life?
No, but it is possible that humans in the future can live there because Neptune has heat at it's core.
Actually, Venus cannot support life for it has various different gases that would not be able to sustain life properly. Although, each planet can sustain life if they had such life forms that had possibly, different features of the body that would make them capable to survive on a remote planet such as Neptune. Hence the term "aliens". Aliens are basically in theory, life figures that are capable to sustain life on these planets. Such…
As of today only one planet in our Solar System can sustain life. However in the past - Venus and Mars well may have had life, but it has died off. With Venus because of it's surface temperature. With Mars, it was because it cooled off after it's initial bombardment and was unable to sustain enough heat (as we know it) to sustain life.
No. It's impossible for life to survive on Neptune. Neptune is a gas giant, which means it has no surface. Life would sink into the planet and be consumed by the molten ammonia core Neptune is freezing cold. Too cold to support life Neptune is stormy. Life would be blown into space There is very little sunlight. Which means plants can't grow. Which means there's no breathable air or food