The results of research in astrophysics and the outcome of exploration of planets by automatic space probes may help to develop better understanding of processes on our planet. The author characterizes briefly the planets of our system to compare their respective natural environments. They are still „natural environments”. It is only on Earth, when humans started to participate in shaping the environment some 500 000 years ago. This participation, negligible at first, became so intensive in the twentieth century that it might bring about an ecological disaster.