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In July 1994, the comet Shoemaker-Levy 9 (D/1993 F2) tidally fragmented and these fragments collided into Jupiter, as per the image below.

enter image description here

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The question is, what mechanisms resulted in these small fragments causing such large explosions in the Jovian clouds?

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Shoemaker Levy 9 was estimated to have released kinetic energy equivalent to 300 gigatons of TNT. That is $1.255 \times 10^{21} {\rm J}$. This release through friction and compression was sufficient to heat the atmosphere to 4000K at first. That in turn should probably be enough to break down the molecular hydrogen and methane, releasing further energy. But that's only my guess. The heating from the impact alone should make a huge fireball.

Sources:

Fragment Size and Mass Estimates

Galileo observations

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An important factor is that the comet had fallen through Jupiter's gravitational field, picking up Jupiter's escape velocity of about 60 ${\rm km/s}$ in addition to whatever velocity it had as it approached the Jupiter system. A paper by D. A. Crawford from the Sandia National Laboratories gives detailed estimates of the sizes of all the fragments at impact. Three of them are estimated at 1km diameter or more, so they were not really small.

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  • $\begingroup$ It's also important to remember kinetic energy scales with the square of velocity. As Jupiter escape velocity is nearly 6x that of Earth, the potential gravitational energy for a given mass is about 6*6 = 36 times larger in Jupiter. $\endgroup$
    – ksousa
    Commented Jan 29, 2021 at 23:32
  • $\begingroup$ FWIW, the kinetic energy density of material at 60 km/s is 1800 MJ/kg. Chemical explosives only have around 10 MJ/kg or so of explodable chemical potential energy. $\endgroup$
    – The_Sympathizer
    Commented Jan 30, 2021 at 1:11
  • $\begingroup$ @The_Sympathizer: I remember the pre-collision estimates suggesting induced fusion. NASA also planned to turn approaching Galello spacecraft to try to catch any reflections of the Jovian moons but never heard word of any result thereof. $\endgroup$
    – Joshua
    Commented Dec 14, 2022 at 20:07

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