Xantoras

Xantoras was an M class planet, the homeworld of the Xantorans. The planet was known for its geological formations, and its historically unstable governments.

History
The Xantoras government had been known to change hands every few years for a long time prior to the 2150s. The government in place in the late 2140s and early 2150s however was overthrown by a militant group in 2153. The new militant group were xenophobic, and believed that aliens should not be allowed on their planet. The previous government had let many aliens on the planet, so the new government instituted a deadline for all off-worlders to leave or they would be imprisoned, and probably executed.

The Denobulan government had sent a team of three scientists to study the rare and unique speleothems that had formed in the large underground tunnels several weeks prior. The team was out of communication range when the new government took hold, so the Denobulan Science Academy could not contact them. The nearest Denobulan starship was several days away, so they asked the Human ship Enterprise to retrieve them.

While the Enterprise was in orbit, an alien starship wanted to land when their reactor breached. As the government was xenophobic, they turned them away even for emergency repairs. Enterprise agreed to dock with them and help with repairs and treating their injured.

The Enterprise sent an away team to climb down the large caverns to retrieve them, given a three-day deadline. While attempting to retrieve the team, Xantoras from the previous government had a skirmish above the caverns. The new Xantoras government told Enterprise they were taking care of it.

The Enterprise away team took a few hours more than the deadline, and on the way back to the ship a Xantoras ship fired on them. But Commander Tucker believed it was just a "kick in the pants" to hurry up to the ship.

Geology
Xantoras was known among geologists as one of the finest collection of preserved specimens known. Its surface was covered with many large and varied mountains and canyons even visible from orbit. But under the surface of the planet was even more note-worthy, as it contained thousands of kilometers of caves and cliffs, and there were many more expected that haven't been mapped yet.

The Denobulan science team that was exploring these caves specifically went to study the largest condensed collections of speleothums known. It contained calcite, aragonite, and even botyroidal flowstones. The leader of the team, Yolen, believed that studying them would provide endless clues into preventing seismic disasters on Denobula. 

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