History of Solar System formation and evolution hypotheses with Uranus having a 98° tilt. The Moon being relatively large with respect to the Earth and other moons which are in irregular orbits with respect to their planet is yet another issue. It is now believed these observations are explained by events which happened after the initial formation of the Solar System. Attempts to isolate the physical source of the Sun's energy, and thus determine when and how it might ultimately run out, began in the 19th century. At that time, the prevailing scientific view on the source of the Sun's heat was that it was generated by gravitational
Mars trilogy help them better adapt to the new worlds; to breathe thinner air (e.g. Russell), or to see better in the dimmer light of the outer planets. The books also speculate on the colonization of other planets and moons in the Solar System, and include descriptions of settlements or terraforming efforts on Callisto, Mercury, Titania, Miranda and Venus. Toward the end of the last novel, humans are taking sub-light colony ships to other stars, taking advantage of the longevity treatments to survive the trip to their destinations. A great portion of "Blue Mars" is concerned with the effects of extreme longevity