New Earth. Book 2 Belle Terre - Dean Wesley Smith

The Starship Enterprise has embarked on its most ambitious assignment yet: to lead a courageous band of settlers to a far-off planet, to defend the fragile colony from alien threats, and to unravel the enigmatic riddles of a brand-new Earth.
A six-month distance from the Federation, the planet Belle Terre offers a new life to more than 30,000 families, pioneers, scientists, go-getters, loners and entrepreneurs, all under the watchful eye of Captain Kirk and his crew. But no sooner have the would-be colonists begun to settle the untamed wilderness of their new home when Spock makes a startling discovery: not only does one of the planet's moons contain a rare ore of almost inestimable value, but that same moon is also violently unstable. Within months, it will inevitably explode - destroying all life on the frontier world of Belle Terre!