Making Mars bigger

An alien race, for reasons of their own, have decided that it's important to make the third and fourth planets in our solar system about the same size and mass. Since they have a strict moratorium on altering planets with clearly visible carbon-based life on them, Mars is the object of their "affections". As a result of their cultural biases, they love iron. Any time they need/want to increase the size of a planet, they use iron to do it. (Yeah, I don't get that either but whatever, aliens, am I right?)

On the day of the drop, they position their ultra-mega cargo freighters full of iron around Mars then let all those gigatons of iron just fall Mars-ward. As you might imagine, the fireworks are spectacular. After the freighters move away, the planet cooling ships move into position but right before they start operations, an urgent call from the Supreme Dear Leader comes in demanding that his entire planet be air-conditioned and the cooling fleet is to report, pronto!

Iron parameters:

• Initial altitude: 150km (all ingots enter freefall form this height)
• Iron initial temperature: 250K
• Speed relative to Mars' surface: 0 m/s
• Individual Iron Pieces: 100 m^3 ingots

Mars must then cool off on its own. With the cooling fleet gone for an indefinite period of time, how long will the aliens have to wait for Mars to cool down to a comfortable temperature for carbon-based life after dumping all that mass on Mars' surface? Assume that atmospheric insulation/cooling effects can be ignored.

Altering Mars' orbit or the orbit of any of the other planets isn't a concern for these aliens, all they care about is Mars. Besides, they have the capacity to "nudge" planets into stable orbits.

(I realize that this is a fairly fanciful way of asking how long it would take to cool off Mars if you dumped enough iron on it to make it the same size as Earth, but it's more fun to write it this way. I also realize that aliens with these logistic capabilities can do pretty much anything they want.)

posted over 8 years ago

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