The Molecular Detachment Device, commonly known as the MD Device, Doctor Device, or Little Doctor as a play on the acronym, was a powerful weapon capable of destroying a planet. The device was cutting edge, a step forward from the nuclear weapons used by humans in the First and Second Invasions. The device, as described in Ender's Game, as a lazer style weapon used to create an atomic state in which electrons cannot be shared. When this happens, the molecule splits into separate atoms, which create a chain reaction in inducing a similar splitting state in surrounding mass. The more massive the target, the greater the firepower of the weapon. Hence, the weapon was generally fired on clusters of starships during the Third Invasion. At the final battle of the Bugger Wars, the Doctor Device was aimed at a planet itself, which resulted in the planet's destruction "within three seconds," as the Ender's Game novel describes.
In the film, the Little Doctor is a massive Hadron-collider like machine carried by a large space ship. It is said to cost billions to make. It charges for some time, and when it was fired on the Formic planet, a pulse of energy ripples over the planet. A shockwave then expands over the surface of the planet, leaving behind multiple burning fires and destroyed structures, similar to an atomic bomb.
The MD device was also used during the attempted Second Xenocide when Lusitania was ordered to be annihilated by Starways Congress. The weapon, however, did not strike its target, as Jane moved the missile back onboard the firing ship, resulting in its deactivation by one of the crew.
In Ender in Exile, it was revealed that the Molecular Disruption Device utilizes similar technology to Interstellar Travel called "Strong Force Field Dynamics". It was discovered first by the Formics to power ships for Interstellar Travel and then the humans made MDD with knowledge of Strong Force Field Dynamics.
- When Jane moved the MD Device back onto the firing ship, it was quickly deactivated, with one of the crew members noting that "the instructions [for deactivation] are written all over this thing."
In Ender in Exile, Ender speculates at the origins of the Little Doctor, saying we adopted the technology from the Formics, but in the first formic war, (Earth Unaware, Earth Afire, and Earth Awakens) Lem Jukes, of Jukes Limited is developing an asteroid molecular disruptor, very similar to the Little Doctor, a year or better before the formics touch down in china. As I said Ender only speculates about the origin of the Little Doctor, and we may have fine tuned it using the formic technology, but it did not originate with the formics.