Planet Of No Return II

Poul Anderson's Planet Of No Return (London, 1971) is a science fiction novel in which the "sciences" are both psychological and physical. Chapter 2 lists five flaws in human thinking:

contradictory beliefs;
inadequate thinking;
surface thinking;
conditioned reflexes;
rationalized emotions.

Chapter 3 lists five requirements for a habitable planet:

atmosphere;
radiation level;
temperature;
gravity;
ecology.

Miners, penal colonists and refugees have colonized Mars, Venus and the Jovian moons with domes and tank food but, for extra-solar colonization, terrestroid planets are sought and not found.

Atmosphere needs oxygen and other gasses, none of them poisonous. Gravity must be great enough to retain the atmosphere but "...not so great as to throw the human body fluid adjustment out of kilter." (p. 21) Edible plants and animals need bacteria, saprophytes and earthworms that in turn require an entire ecology. Separate evolution has probably produced inedible or poisonous organisms and cannot have duplicated all the vitamins.

An astronomical expedition has detected the first ever terrestroid extra-solar planet in the Lagrange system, so, at the beginning of the novel, a Lagrange Expedition II is being organized, Expedition I having disappeared. At first, I found the reference to "Lagrange" confusing because the term is applied to orbital points within the Solar System but here it is the name of a star.