DS9 Season 4 Episode 8 Little Green Men

Plot

Quark receives a shuttle that his cousin Gaila has been promising him for years. For its maiden voyage, he takes his brother Rom and nephew Nog to Earth, where Nog has been accepted to Starfleet Academy. After they leave Deep Space Nine, Rom discovers that Quark intends to make the trip financially profitable by smuggling an illicit load of volatile kemocite.
As the ship nears Earth, Rom finds that they are unable to drop out of warp, possibly due to sabotage by Gaila. However, venting the warp exhaust through the kemocite cargo enables the ship to drop out of warp. Unfortunately, in doing so the ship and crew are thrown back in time to July 1947 and crash land near Roswell, New Mexico. The Ferengi awake on a U.S. military base, where the Americans believe them to be Martians. After Rom repairs their malfunctioning universal translators, Quark begins negotiations with the humans, whom he considers backward and gullible, to sell advanced technology from the future. He brags to Rom and Nog in private that "within a year we'll be running this planet," and dreams of cultivating a vast Ferengi economic empire.
Unknown to the Ferengi, Constable Odo stowed away aboard the shuttle with them to investigate the kemocite smuggling and thus was also thrown back in time. Using his shapeshifting abilities, Odo is able to move about the base locating and repairing their spacecraft. Having disguised himself as a guard dog to gain entry to the room where the Ferengi are being held, he tells Quark that they must try to preserve the timeline and not alter Earth's history. Quark, Rom, and Nog are interrogated by an army officer convinced that they have hostile intentions, but escape from custody with the help of a nurse and her fiancé, a professor who was brought to the base to try to establish dialogue with the aliens.
By harnessing the energy of an atomic bomb test scheduled for that morning in Nevada, Rom is able to use the remaining kemocite to return them to their proper time. After dropping off Nog at Starfleet Academy, Quark has to sell the damaged spacecraft for salvage and he, Odo, and Rom return to Deep Space Nine. As the episode ends, Odo arrests Quark for smuggling contraband.