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Largest possible rocky planet
Alrighty. I want to try something with this. I've been drafting a large, high-G planet Phlegethon for the stalled Lethe EG article anyway.


Very large planets - a few hundred Earth masses - are a wee bit challenging to create. However, rocky cores of gas giants may reach into the 10's of Earth masses, especially with a little handwaving and invoking the words, "high metallicity system."

Further, it'd be nice to make this a habitable - or fairly human-accessible - planet. I don't see a problem genetweaking folks to 3-5Gs with OA's genetech. So, that's another reason to cut out planets with 39Gs and hundreds of Earth masses.

If I used the chart correctly, a 30 Me peksov...perksv...peros...rocky planet will have a radius of 2.8x Earth. That gives a 3.8G surface gravity. Not bad, and almost 8x Earth's surface area.

Next issue: gas.

Big planets tend to accumulate too much atmosphere. However, there's a fix for that in OA: roaster orbits, supernovae, and other high energy events. The "Phlegethon" I was planning for the neutron star Lethe saw:
1) Not one, but two supernovae that formed proto-Lethe neutron stars, and
2) The neutron stars colliding to form Lethe with a sizable bang
3) Starquakes are available

It's not a question of "Can you remove enough atmosphere that way?" But rather, "Can Phlegethon survive?"

Next issue: core temperatures.

Phlegethon is 30 times Earth's mass but at 8 times the surface area takes 3.75 times as long to cool. Well, it isn't too much to ask for Phlegethon to be 9 or 10 billion years old, is it? It probably took a while for the twin neutron stars to spiral down, too, so there's another need for the system to be old. 9 billion years would leave Phlegethon shedding heat like Earth at 2.4 billion years of age. Hot, but not magma ocean hot.

Next issue: habitability.

This is sort of a lost cause without getting into paraterraforming. Phlegethon isn't orbiting a cheery, lifegiving star. It orbits a neutron star. It probably has traces of a hydrogen-helium atmosphere; anything else that seeps out of the crust will freeze.

So, did I get that right? 30 Earth masses, 3.8G, 2.8 Earth radii? Is that a reasonable way of shedding the atmosphere?
Mike Miller, Materials Engineer

"Everbody's always in favor of saving Hitler's brain, but when you put it in the body of a great white shark, oh, suddenly you've gone too far." -- Professor Farnsworth, Futurama

Messages In This Thread
Largest possible rocky planet - by stevebowers - 06-25-2015, 02:54 AM
RE: Largest possible rocky planet - by Rynn - 06-25-2015, 03:00 AM
RE: Largest possible rocky planet - by Cray - 06-25-2015, 06:13 AM
RE: Largest possible rocky planet - by Cray - 06-25-2015, 09:53 PM
RE: Largest possible rocky planet - by radtech497 - 07-04-2016, 10:26 AM

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