When Planets Collide " Think fast Mr . Spock ! A freak impulsion is creating galactic disaster ! " Summary . 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 planet s . 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 humanoid s 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 supernova ed and one ten - thousand ton section did not disintegrate . Vulcan scientist s 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 ! " " " " Think we ' re being boondoggled . . . " put on , " Mr . Spock ? " " " " I . . . do not think so , Captain ! " " " " Yiiipes ! Be - bejabbers ! Look at that ! " " " " 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 ! " "