Tony Rothman’s The World is Round was published in 1978.
Wealthy businessman Pike mounts an expedition to Barythron, a solar system just ten light-years from his home world, Two-Bit. Expedition crew: Pike, Hendig (who has visited Barythron and returned with tales of treasure), Valyavar, and Stringer.
Six years later (or ten, depending on your frame of reference), the starship Crimsonarrives at Barythron and the crew wakes from cold sleep to discover that Hendig’s tale is quite true. A planet fifty times the size of Two-Bit orbits the sun of Barythron. Now one might expect that such a large world would be a gas giant — but it isn’t. It appears to be quite solid, with habitable conditions on its surface. Not only that, it’s inhabited. A scientist would question this implausibility and advise extreme caution. But Pike finds scientists annoying and deliberately didn’t bring any.
The crew divides into two parties — Pike with Hendig, Stringer with Valyavar — and then heads to the surface. It does not take long for things to go very very wrong.