When Planets Collide
Think fast Mr. Spock! A freak impulsion is creating galactic disaster!

Summary
"Captain's log, Star date 23:009 – Top brass studied a curious pick-up on the screen of the 's TV space scanner…"

The crew has been tracking UB (unidentified body) blips that appear to be on a direct collision course in the Alpho galaxy. They set course toward them to attempt to figure out a way to prevent them from colliding. Five days later, the blips are identified as planets. They are so large that the resulting shock waves would push the planets orbiting Alpho out of orbit. Fortunately, it appears that there is no life on the planets.

The ship heads toward one of the planets, reaching it a galaxy day later. Captain Kirk forms a landing party to go to the planet and set hydrogen charges. Included are Spock and Scotty. They beam down to the surface and find that the air is breathable. However, a nearby dome fires a strange ray at them, encasing them in individual anti-gravity bubbles. The bubbles are drawn toward the dome where there are humanoids waiting for them. The crew are removed from the bubbles and strapped into chairs, and electric impulses penetrate their brains.

The aliens begin to interrogate the crew, but Kirk insists that they are only there to help. However, the shocks continue. Kirk reaches for his phaser, shoots the leads and restraints holding him in his chair, and then frees Spock and Scotty from their own chairs. He shouts in Space Esperanto at their captors, aiming his phaser at them. He repeats the information that another planet is on a collision course, and that it will occur within three galaxy days. As they explain the options, Kirk is shocked by what appears to be an enormous fire approaching.

The aliens explain that it is their artificial sun and how they survive on the planet Morti. It took them many time-space centuries to develop. They step out onto the balcony, and find that they have traveled on an elevator below the surface of the planet. For many miles beneath the surface, a civilization prospers with farmland, rivers, and buildings. Because they need to conserve thermo-hydrogen fuel, they only use the sun force for five hours each day, a quite sufficient amount.

The crew notes that time is running out and beams back to the Enterprise to visit the other planet. As they approach it, once again, no signs of life, but there are mountains of an unknown, highly active, metallic ore. As the vessel nears the planet, Scotty is slammed into a bulkhead. There is a small rock that he picked up on Morti, and it appears to be magnetized from the planet below. The force on the rock seems to be stronger than any electro magnet!  That is the reason for the impending collision, the strong magnetically attractive pull between the two planets.

Before beaming down to the second planet, Spock is determined to find some mineral to put between the planets to block the forces, but is completely unable. Kirk, Scotty, Spock, and Dr. McCoy beam down to the planet and Kirk radios up for the atomic explosive charges to be sent down. Spock and Kirk cover one end of the mountain range, while Scotty and McCoy take the other. They carefully make holes for the charges with their phasers and plant the explosives. As they prepare to beam back aboard the Enterprise, Spock spots movement, something that appears to be a living form. However, they can find nothing.

Suddenly, part of the mountain opens up and Spock is yanked inside and pushed down a slide, deep into the mountain. The others follow, spotting the alien who grabbed Spock heading down the slide himself. At the bottom, Spock encounters several humanoids. They demand to know who he is, just as the other alien arrives telling them that there are more enemies coming. The aliens light-bind the crew while the leader can "weigh the truth of their words."

In the throne room, Spock explains the situation, but learns that the mountains power the alien machinery and keep them alive, a situation that has been in place for a million million galaxy years. With less than 26 hours before the collision, Spock suggests that there may be a very slim chance of solving the problem, and the crew beam back up to the Enterprise.

On the ship, Spock hurries to a deep galaxy probe scopescreen. Kirk asks if he's looking at the luminous space particle from the star named Doona. Doona supernovaed and one ten-thousand ton section did not disintegrate. Vulcan scientists had studied it for centuries, with its hardness ten times that of space diamonds, and it "radiating a repelling force of the tenth magnitude."

Kirk decides to head for the particle, ordering "all rockets on full!  Star course deep galaxy penetration!"  He tells Spock to give them the exact heading, and heads for the lab to rig up an electronic tow rope. On his way, he notes that the area of space is filled with meteor swarms, and worries that he may sacrifice the Enterprise to save two planets.

They arrive at the particle and wrap it with the bands of magnetic power and head back toward the planets. They start to increase speed and hit their top safety towing speed of 110,000 miles a second. Just as they do, a meteor swarm appears off the starboard bow, catching the Enterprise in the middle of the swarm. Rocks puncture the hull, rocking through the bridge for three minutes, until the ship manages to pass through.

Thirteen hours later, the Enterprise arrives at the planets with four galaxy minutes to spare and drags the particle right between the planets. The planets rush toward it and begin to shudder as they slow. They come to a halt, likely causing a moderate earthquake on each one. Kirk notes that the repellent power should hold for centuries, and hopes that "by that time the Enterprise will know how to really solve this problem!"

Memorable quotes
"Magnetic chairs… holding flesh down like metal!  What do you think they're up to, Mr. Spock?"
"I can only deduce that they are testing us! Perhaps seeking to prove what they do not believe!"
 - Kirk and Spock, as they begin to be interrogated

"Think we're being boondoggled… "put on," Mr. Spock?"
"I… do not think so, Captain!"
"Yiiipes! Be-bejabbers! Look at that!"
 - Kirk and Spock, discovering the artificial sun and underground world

"If there was time, I'd blow the whole cussed planet up… it's certainly no use to the galaxy!"
"No, I gather not, Captain!  Unless, of course… it has some unknown purpose among the stars… such as Earth must have had at one time!"
"Oh, come on… spare me that Vulcan philosophy of yours right now, Mr. Spock!"
 - Kirk and Spock, discussing the impending destruction of the planet.

Background information
 This story was reprinted in Enterprise Log 1 and a later reprint of that volume from the Star Trek: The Key Collection series.
 The title "When Planets Collide" may have been intended as a homage to George Pal's 1951 film, When Worlds Collide. The concept of a super-dense nova fragment was seen in , and a planetary collision was revisited in . Coincidentally, the "Ship in a Bottle" planetary collision bore a remarkable similarity to a similar collision in Pal's film. 
 The photograph of Spock on the cover was taken from .
 The story art includes a cutaway view of the Enterprise that depicts it as much smaller than canon productions, apparently having only about a half-dozen decks in total, with the Secondary hull having only two decks and small enough that a control room with four seats takes up half its length. The text next to the image contradicts it by referring to the ship being the largest spacecraft "in the universe" populated by hundreds of crew.

Creators
 Based on Star Trek created by Gene Roddenberry
 Writer: Dick Wood
 Artist:  Alberto Giolitti

Characters

 James T. Kirk   captain.
 Spock  Vulcan Enterprise exec and science officer.
 Leonard McCoy  Enterprise chief medical officer.
 Montgomery Scott  Enterprise chief engineer.

References
 Alpho  Star. Kirk notes objects detected in the "Alpho galaxy", although this nomenclature presumably refers to a point within the Milky Way Galaxy, since Alpho was noted to have other planets orbiting it.
 Doona  Ancient supernova.
 Morti  One of the rogue planets.
 The Inicrusts  The aliens living on the other rogue planet.

fr:When Planets Collide (Gold Key Comics)
Comics