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Alderaan: Details

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• Introduction
• Alderaan's Shield
• Acknowledgements
• References

For introductory, cursory remarks about the planet Alderaan, refer to the general commentary about the planets of the STAR WARS films.

The superlaser beam strikes the planet and a bright glow spreads away from the point of contact and expands to cover the entire globe within a few frames of the movie. Let's consider several possible explanations for the nature of this time-varying glow.

• Reflected glow from the superlaser beam: We see any superlaser/turbolaser/blaster beam because its constituent massless quanta can radiate or decay to produce visible photons as a byproduct, and this emission shines in all directions off to the sides, not just the original beam direction. The glow on the face of Alderaan might be explained as a reflection of the beam's lateral emissions. This illumination should be maximum where the beam hits the globe, and appear dimmer with radial distance. However the glow on Alderaan spreads and brightens, and this doesn't make sense because the superlaser beam (as a direct light source) remains constant (from the camera's point of view).
• Directed illumination: The glow could be a conical beam of light shone from the Death Star witihin some angle surrounding the superlaser beam. Imagine it as something like a spot-light that rapidly expands in angle. But why would the superlaser weapon need such an effect, or (alternatively) what could account for such a highly directed side-effect that varies even while the superlaser remains constantly intense? This explanation seems implausibly non-functional and complicated.
• Beam/shield interaction: According to Lord Vader [ANH novel, pp.129-130] Alderaan's defences were as good as any in the Empire. That implies a full planetary shield system like that of Coruscant [e.g. The Last Commmand]. Every ray shield attempts to limit the damaging effecs of an incident beam by inducing it to split into a cascade of less intense daughter rays, which are scattered through large angles, and also by direct absorption and re-diffusion of incident energy. Absorbed energy is dumped into internal heat sinks for later, gradual irradiation (e.g. in the form of relatively harmless neutrinos from some starships [AOTC:ICS]). The spreading glow on the face of Alderaan may be the visible consequence of superlaser beam power being partially diffused away from the point of contact. After this momentary effort, the shield is overwhelmed (both in terms of its diffusive and absorptive capacities) and the planet explodes.

The visible beam/shield interaction is presently simplest and most self-consistent explanation. This commentary proceeds by adopting that conclusion.

In this case the destruction of Alderaan is a valuable demonstration of some aspects of shield physics. In the interval between frames 2 and 3, the extent of the glow has increased (approximately) from ¼ to ½ of the planetary diameter. If the movie has the standard 24/s frame rate, then the characteristic speed for the diffusion of an energy surge in the Alderaan planetary shield is approximately 0.25c. This is an interesting measurement in shield physics. Do other shields handle incident beams with a comparable diffusion speed? Is this speed a characteristic of the propagation or fluxes of the energy quanta that carry the invisible field effect that we call a "ray shield"?

Seven frames from the beginning of the destruction of Alderaan, starting from the incidence of the Death Star's superlaser beam, proceeding through the spread of a shield interaction and leading to the first eruptions of escaping mass.

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Special thanks are due to, in alphabetic order:

• Michael Wong for the video frames of the Alderaan explosion from the fullscreen ANH DVD.

References

• Attack of the Clones: Incredible Cross Sections, Curtis Saxton et al., DK Publishing, 2002.
• The Last Command, Timothy Zahn, Bantam, 1993.
• STAR WARS [novel of ANH movie], George Lucas, Del Rey, 1976.
• STAR WARS IV: A New Hope, George Lucas et al., Lucasfilm Ltd., 1977 (DVD 2004).