If they could, we would all be very worried! While some planets have boiling hot cores, this is not enough to cause a planet to shatter let alone suddenly explode. As far as astronomers know, there is no internal mechanism or other phenomenon that could ever cause a planet to fly apart. Contrary to science fiction, planets are stable and causing one to explode would require some chemical or nuclear process which can provide an explosive punch of energy.
For example, to detonate the Earth, a ball of uranium with a diameter of some three miles at the core would be required. While it is impossible to kick-start a fusion reaction at a planet’s core, uranium fission is possible provided no neutrons are absorbed. Of course, in the case of our Earth, dissembling its structure against its own gravitational binding energy would be difficult since its interior is teeming with neutrons which would stop fission in its tracks. Additionally natural processes alone would not be able to create such a pure and concentrated ball of uranium.
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