What planets are you talking about? Well, the one with a good level of oxygen ( allows humans to breath and forms the ozone layer that protects us from the Suns harmful rays) and hydrogen( mixes with oxygen to make water). The suns impact on the planet affects the whole life on it, so you need to take that into consideration. List me the four planets and I can give you a much better explanation.
This person is feeling lonely and depressed
To be honest, I'm not that sure on which one it is, but given choices lead me to think is the nervous system, probably because that's the reason our bodies are functioning, and compared to all other systems, the brain and the nervous system are needed for survival, otherwise you wouldn't be living.
