Alderaan: Planet of Traitors
Last Revised: 2007-05-29
Welcome, citizen of the Empire. Before his tragic death in ANH, Grand Moff Tarkin punished the traitorous planet Alderaan with the original Death Star's superlaser weapon. The planet Alderaan was home to the notorious Leia Organa-Solo, who was instrumental in the destruction of the Death Star and whose brother, Luke Skywalker, somehow corrupted the previously honorable Darth Vader to their cause. The political leadership of Alderaan heavily supported the rebellion at the time it was destroyed, and in spite of Leia's claims to peacability, had planetary defenses as strong as most other Core worlds.
As can be seen from the above frames, Alderaan was very heavily shielded. It dispersed a small portion of the Death Star's superlaser blast, which is no mean feat. The radiant dispersion effect can be seen beginning at a point well outside the atmosphere of Alderaan, so it demonstrates the size and scope of Imperial planetary shielding technology (one of the reasons the Death Star was developed in the first place). Although the people of Alderaan professed to be peaceful, they were not only supplying the rebellion with financial aid but they were also involved in a rearmament program. After the fall of Palpatine's Empire, New Republic propagandists made the ludicrous claim that Alderaan was totally unarmed at the time of its destruction, even though it had placed warship construction orders with, among others, Kuat Drive Yards (ref. Slave Ship). Presumably, these purchase orders were the act of a peace-loving, unarmed people ... this "no weapons" claim is merely another example of the completely one-sided, revisionist history that was disseminated throughout the galaxy during the time of the New Republic.
As if the propaganda of the New Republic weren't vexing enough, some who doubt the power of the Empire have taken to claiming that the 2.1E32 joule lower limit for the energy of a Death Star blast is too high. In reality, it is an immutable lower limit and it is actually far too low. Let us look at some 24 fps indexed pictures from the destruction of Alderaan:
The explosion of Alderaan, frame #42130 (click to enlarge)
The explosion of Alderaan, 20 frames later (click to enlarge)
At 24 frames per second, 0.83 seconds pass between those two pictures. If Alderaan was roughly Earth-like in size, then the first frame shows a superheated debris cloud roughly 17500 km wide, with large trails of debris that extend to a width of roughly 31000 km. The second frame shows a debris cloud that is 37500 km wide, and the fastest-travelling debris has been thrown so far that it is no longer visible in the screen. Some of the fastest-moving debris pieces are hundreds of kilometres wide.
Therefore, the main edge of the cloud has covered roughly 10,000km in a time of 0.83 seconds, for an average velocity of 1.2E7 m/s. Some of the debris is obviously travelling much more quickly than the main edge of the cloud, but some of it is travelling much more slowly as well. If we substitute the mass of an Earth-like planet (5.97E24 kg) and the velocity of the Alderaan debris cloud's main edge (1.2E7 m/s) into the kinetic energy formula KE=½mv², we will find that the energy state of the cloud (not including any increase in thermal energy) is roughly 4.3E38 joules higher than the initial energy state of the planet.
Of course, the average velocity of the cloud will be lower than the velocity of the main edge (although it is noteworthy that the fastest-moving chunks, some hundreds of kilometres in width, are being ignored). If we assume a roughly symmetrical velocity distribution from 0 to 1.2E7 m/s so that the average velocity is 6E6 m/s, and plug that into the kinetic energy formula, we will find that the result is 1E38 joules.
Some doubters claim that time compression might have been employed in the above shot, but the same shot also contains the superlaser beam itself, and it is obviously not time-compressed. Moreover, if the explosion really were so slow, there should have been much more material left behind when Han Solo showed up scant minutes later.
The Alderaan debris cloud expanded at roughly 4% of the speed of light. If we assume that the inside of the cloud had an even simple distribution between 0 and 4% of the speed of light, its average velocity would be roughly 2% of the speed of light, so its kinetic energy would be roughly 1E38 joules. This is, of course, a staggering amount of energy. Try to imagine seizing the entire planet Earth and hurling it like a football at 6 million metres per second, or try to imagine how much power the Sun generates in eight thousand years, and you'll have some idea of how much energy it takes to blow apart a planet the way Alderaan was destroyed.
Addendum: DVD Update
Two more versions of the Alderaan explosion have been produced since the original in 1977. I have digitized all of them: the Classic version, the late-90s Special Edition version, and the 2004 DVD version. If you have a current version of the Divx video codec installed, you can view them by clicking on the links above. Note that all 3 clips are presented in the original cinematic 24 fps framerate.
Rough scaling reveals that not much has changed. In all three versions, the blast strikes the planetary shield causing it to glow, so that the shield holds off the blast for roughly 0.13 seconds.
The first stage of the explosion lasts for roughly 1 second. At this point, the debris field is roughly 35,000 km wide (assuming Alderaan was of Earth-like size), thus giving its outer edge a velocity of roughly 11,000 km/s. There is also a "fire ring" which is moving at roughly 40,000 km/s.
Strangely enough, there appears to be a second stage of the explosion at this point, even more violent than the first one. The physical mechanism behind this two-stage explosion is unknown; perhaps the beam is continuing to fire some invisible component after the visible portion has ceased. Some have suggested that it proves the presence of some kind of exothermal reaction in the exploding mass, but they cannot explain why such a reaction would suddenly kick in when the reaction fuel is in the midst of dispersing; normally one would expect a reaction to take place when the reaction mass is most dense, not when it's already flying apart. In any case, this secondary stage hurls more planetary debris outwards and creates a second "fire ring" which rapidly overtakes and consumes the first one, continuing to move outwards at well over 1E8 m/s (one third the speed of light).
By the final frame, it is becoming difficult to ascertain the width of the debris field as it disperses. However, it appears to be similar to its initial expansion rate, somewhere between 10,000 to 15,000 km/s. This is consistent with the 12,000 km/s figure from the original version, which means that we are still looking at an energy estimate in the 1E38 J order of magnitude, regardless of which version you use.
The "fire rings" are something of a physical conundrum; no one knows what they are or how they are generated. There is no reason why the energy of the superlaser should create fire rings, and those who confuse the Death Star superlaser with the Galaxy Gun chain reaction cannot explain why a chain reaction would preferentially produce such rings either; normally the effects of a chain reaction will reflect the shape of the fuel, rather than arbitrarily forming into a flat ring.
Contrary to the claims of some Federation propagandists, the energy figures derived from the SE and DVD versions are not much different than the one derived from the original. The key differences are of appearance and composition; the original version showed a heavy gaseous debris cloud expanding at 12,000 km/s, with scattered particles being hurled away at relativistic velocities. The SE and DVD versions are actually more energetic; they show a main debris cloud of expanding at roughly 10,000 to 15,000 km/s, with a "fire ring" being hurled away at relativistic velocities.