Priplanus

Priplanus was the first planet that the Jupiter 2 crashed on in “Island in the Sky.” The Robinson family spent the rest of first season of the series on Priplanus. Will gives the name of the planet in “Return from Outer Space.” It had two moons and is an extremely small planet. It was located on the opposite side of the galaxy from the planet in Sector 6.30 where the Robinsons would settle in season two, and was ten million light-years from the home world of the Keeper.
Priplanus had an highly elliptical orbit around its sun, resulting in extremes of temperatures on the planet. Its topography included prairie, mountains, open water, badlands and bogs from which dangerous gases escaped. There were occasional patches of quicksand in the area of the Robinsons’ encampment, and “bottomless” pits of cosmic dust nearby.
Priplanus had an intelligent species of cyclops-like creatures in the past since the Robinsons found evidence of their existence in caves (“There Were Giants in the Earth”) and was also home to a militaristic civilization contained in an underground city while the Robinsons were there (“The Lost Civilization”).
The planet was also home to a wide range of strange animal and plant life. The growth of some to gigantic proportions may have been due to a particular bacterium in the soil. Some examples of the life on the planet were the giant cyclopses, the bloop, and giant cyclamen plants.
Priplanus was destroyed in the first episode of the second season (“Blast Off Into Space”) by the miner Nerim, who used too much blasting powder in his search for cosmonium. The planet’s destruction was not shown, but the opening narration in “Blast Off Into Space” said “a cataclysmic explosion would rip apart the planet’s core, and disintegrate their entire world into galactic dust.”
“Priplanus” is the spelling used in the subtitles of the DVD release of the series, but the Internet Movie Data base uses the spelling “Preplanis.” The planet seen in “The Derelict” was different from the one in “No Place to Hide;” the visual was probably changed to avoid viewers confusing the earlier visual with the planet Mars, although Will does suggest that they may be on Mars in “The Hungry Sea.”