Wednesday, June 16

Geek

Thought For The Day, Planetary Engineering Edition

If you were to construct a planet out of the lightest known solid, with Earthlike surface gravity, it would have a diameter of 44 million miles and a surface area of 30 million Earths.  Rotating once per 24 hours, at the equator you would be moving at approximately 1% of the speed of light.

Unfortunately (a) the bulk strength of aerogels is such that it would collapse instantly into a ball of seifertite only 2.7 million miles in diameter and with a surface gravity of about 2500G and (b) if it didn't, the rotational speed at the equator would exceed the escape velocity and the entire planet would immediately fly apart.

Apart from those minor issues, it would be an interesting place to live.

Posted by: Pixy Misa at 03:24 AM | Comments (7) | Add Comment | Trackbacks (Suck)
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1 Planning to write a Hal Clement novel, are we?

-j

Posted by: J Greely at Wednesday, June 16 2010 08:26 AM (fpXGN)

2 Just playing with the numbers for now. wink

Posted by: Pixy Misa at Wednesday, June 16 2010 10:10 AM (PiXy!)

3 Could you manage to achieve a rotational speed (abandoning a 24 hr day, unfortunately) such that the planet avoids becoming compressed due to gravity, and doesn't fly apart from rotational speed?

Posted by: JPGA at Wednesday, June 16 2010 09:57 PM (OGXok)

4 Getting a discus-shaped planet like Mesklin?  I don't think so; gravity even at the poles would be enough to crush the aerogel. 

Aerogels are amazingly strong for their weight (lighter than air, yet they can support thousands of times their own weight), but they are porous and hence compressible.  Apply enough pressure and it will just go crunch and leave you with a solid silica that's nearly as dense as the Earth.

Posted by: Pixy Misa at Wednesday, June 16 2010 11:21 PM (PiXy!)

5 Your post-compression object would be about three times the diameter of the sun. Seems like it might keep compressing and start to glow. (Though I doubt that fusion would take place; oxygen and silicon are not good fuels.)

Posted by: Steven Den Beste at Thursday, June 17 2010 01:27 AM (+rSRq)

6 Good point.  I wonder if I can find the details on what temperatures and pressures are required to initiate fusion of silicon and oxygen.

...

Yep.  Okay, my planet works out to about 1.4 x 1032 kg, about 70 solar masses.  Silicon and oxygen will fuse in stars over about 10 solar masses (with a stellar core over about 2.5 solar masses) once hydrogen and helium start to become depleted.

So under our laws of physics, my planet would go supernova and leave behind a black hole.

Posted by: Pixy Misa at Thursday, June 17 2010 03:45 AM (PiXy!)

7 Mmm.  And specifically a type II supernova, the big flashy kind.  (As opposed chiefly to type Ia, the astronomer's "standard candle".)

Posted by: Pixy Misa at Thursday, June 17 2010 03:52 AM (PiXy!)

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