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| Kiryu in Godzilla: Tokyo S.O.S. |
Mechagodzilla (Millennium Era), better known as Kiryu, is a version specifically designed with the purpose of destroying Godzilla, much like its previous incarnations. However, it possesses unique characteristics that make it particularly interesting, the most notable being the Absolute Zero Cannon, its most powerful weapon.
The key question is:
What is the weapon’s energy output?
In the film, the blast is shown pulverizing three skyscrapers in Tokyo. Therefore, we will attempt to estimate the weapon’s energetic potential as reasonably as possible, acknowledging that this is fiction while still applying consistent physical principles.
Volume and Mass Building Estimation
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| Godzilla Against Mechagodzilla 2002 |
Based on available information, the destroyed buildings are:
Shinagawa Prince Hotel New Tower:
Height: 143 m - Ground floor area: 2050 m²Annex Tower :
Height: 109 m - Ground floor area: 2046 m².Shinagawa Goos (demolished in 2024) :
Height: 118.7 m - Length: 160 m - Width: 30 m
Since no official structural mass data is publicly available for these buildings, their mass is estimated based on geometric volume. For Shinagawa Goos, with dimensions of 118.7 m in height, 160 m in length, and 30 m in width, the total idealized solid-block volume is 569,760 m³. However, buildings are not solid structures; on average, the actual structural volume represents approximately 10% of the total geometric volume, with the remainder consisting of interior empty space. Therefore, the effective constructed volume is estimated at 56,976 m³. Assuming an average structural density of 2700 kg/m³ — a reasonable value considering materials such as steel (7850 kg/m³), concrete (2400 kg/m³), glass (2500 kg/m³), wood (700 kg/m³), and plaster (800 kg/m³) — the resulting estimated mass is 1.538352 × 10⁸ kg.
Applying the same methodology to the Shinagawa Prince Hotel New Tower, with a height of 143 m and a base area of 2050 m², the total volume is 293,150 m³. Taking 10% as structural volume yields 29,315 m³ of constructed material. Multiplying by the same average density of 2700 kg/m³ results in an estimated mass of 7.91505 × 10⁷ kg.
Finally, for the Annex Tower, with a height of 109 m and a base area of 2046 m², the total volume is 223,014 m³. Its estimated structural volume (10%) is 22,301 m³, which, when multiplied by the same average density, produces an approximate mass of 6.02127 × 10⁷ kg.
With the mass estimates established, we now proceed to the next stage: determining the energy required for destruction.
Destruction Energy
According to the film, the Absolute Zero Cannon is capable of cooling its target to absolute zero (0 K = −273.15 °C), effectively destroying it at the molecular level and causing the structure to collapse under its own weight.
This capability is further supported by the official guide, which explicitly states that the weapon freezes the target completely to absolute zero.
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| Godzilla Against Mechagodzilla Super Complete Works Pag. 17. 胸部から撃ち出す超低温の光弾。 その威力は、分子の運動を停止させ、 対象を瞬時に凍結。 凍結した物体は、わずかな衝撃で粉砕する An ultra-low temperature light projectile fired from the chest. Its power stops molecular motion, freezing the target instantly. The frozen object can be pulverized with a light impact. |
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Godzilla Against Mechagodzilla Super Complete Works Pag 34. 絶対零度近くの超低温光線を発射する。 原子レベルで分子運動を停止させ、 対象を瞬時に凍結・粉砕する。 エネルギー消費は機龍全体出力の40％に達する It fires a beam of ultra-low temperature, close to absolute zero. At the atomic level, it stops molecular motion, instantly freezing and pulverizing the target. Energy consumption reaches 40% of Kiryu's total power. |
Determining the required energy becomes more complex at extreme temperatures, since classical physics breaks down as we approach absolute zero (0 K). According to the third law of thermodynamics, reaching exactly 0 K would require infinite energy.
However, since this is a fictional scenario, we apply a simplified constant specific heat model to estimate the energy required to cool the material from 25 °C (298.15 K) down to 0 K.
Using:
For 1 kg of concrete:
c ≈ 800 J / ( k g ⋅ K )
Δ T = − 298.15 K
Total mass of three buildings:
This only accounts for temperature change, not molecular disintegration.
To destroy matter at the molecular level, energy equal to the sum of all chemical bond energies must be supplied. Concrete is primarily composed of silicates, with silicon dioxide (SiO₂) serving as a representative component. The silicon–oxygen (Si–O) bond energy is approximately 452 kJ/mol, and the molar mass of SiO₂ is 60.08 g/mol. In 1 kg (1000 g) of SiO₂ there are approximately 16.64 moles.
Energy per kg:
Applying this value to the combined mass of the buildings (293,198,400 kg).
Total energy:
Approximately 65 times greater than the thermal cooling estimate
If this represents 40% of Kiryu’s total output:
In summary, by estimating the Absolute Zero Cannon’s energy under two approaches —thermal cooling to 0 K and molecular destruction via chemical bond dissociation— we obtain significantly different results. Simple thermal cooling of the three buildings requires approximately 7.0 × 10¹³ J (16.7 kilotons of TNT), whereas molecular disintegration increases the requirement to 4.41 × 10¹⁵ J (≈1 megaton of TNT). If this latter value represents only 40% of the weapon’s total capacity, then its maximum output would reach approximately 2.6 megatons of TNT, placing it firmly within a high-end urban-level destructive range.
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