What would happen if you could blow up a planet for real?

[sshai45]

Hi.

(Not sure whether this should go in the "science fiction" or "real science" section, since while it's about something often featured in science fiction, I'm asking about real science.)

We've all (well, perhaps not literally _all_, but you get the point) seen those movies where they blow up planets -- Star Wars, etc. But what'd happen if one could do that for real? If one had a way to generate an enormous amount of energy in a beam form and shoot an Earth-like planet with it -- with enough to blow it up? What would the explosion actually look like?

 

[Ryan_m_b]

To totally destroy a planet (i.e. not just chip tiny bits off that could fall back down or go into orbit) you need to put in more energy than the gravitational binding energy of that planet. For Earth that is ~2.25e32J which is about the amount of energy the Sun puts out in a week.

If we propose an unobtanium Dyson sphere that reflects all the Sun's output onto the Earth then over the course of a week you would see the Earth heating up and evapourating until nothing is left.