Author Topic: v2.1.1 Bugs Thread  (Read 47148 times)

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Offline jamac41

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Re: v2.1.1 Bugs Thread
« Reply #255 on: November 25, 2023, 06:40:18 PM »
A possible bug, though it may also be `the wonders of space': I've found a planet of unusually low density - included in the attached screenshot, it has the same gravity as Mars but over 13 times the volume.  By my calculations, it has a density of a little under 0. 29g/m3.  For comparison, pumice has a density of 0. 25 g/m3.  Maybe it's a Naboo-style planet with a cave system at its centre?
 

Online nuclearslurpee

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Re: v2.1.1 Bugs Thread
« Reply #256 on: November 25, 2023, 07:06:01 PM »
A possible bug, though it may also be `the wonders of space': I've found a planet of unusually low density - included in the attached screenshot, it has the same gravity as Mars but over 13 times the volume.  By my calculations, it has a density of a little under 0. 29g/m3.  For comparison, pumice has a density of 0. 25 g/m3.  Maybe it's a Naboo-style planet with a cave system at its centre?

By my calculations, the planet in question appears to have a density of 2.2 g/cm3 which seems reasonable. Mars is 3.9 g/cm3 for comparison.

Quick maths:
    M = (ag * D2) / (4 * G)   
where G = 6.67E-11 in SI units.
    V = (PI / 6) * D3
  rho = M / V = (3 * ag) / (2 * PI * G * D)


Mars: rho = (3 * 0.38 * 9.81) / (2 * PI * 6.67E-11 * 6.8E6) = 3.9 g/cm3.
Tau Ceti VII: rho = (3 * 0.91 * 9.81) / (2 * PI * 6.67E-11 * 29E6) = 2.2 g/cm3.

Note that the gravity isn't actually the same as Mars (0.91 Gs vs 0.38 Gs), but if it were the density would still be a comfortable 0.92 g/cm3.

You can also check the density in SM mode by selecting the body and clocking the "Modify Body" button in the lower-right panel. I'm fairly sure this density is used to compute the gravity, not vice-versa, so you can be assured that the range of values is reasonably realistic.  ;)
 

Offline jamac41

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Re: v2.1.1 Bugs Thread
« Reply #257 on: November 25, 2023, 07:28:38 PM »
Quote from: nuclearslurpee link=topic=13078. msg166214#msg166214 date=1700960761

By my calculations, the planet in question appears to have a density of 2. 2 g/cm3 which seems reasonable.  Mars is 3. 9 g/cm3 for comparison.

Quick maths:
    M = (ag * D2) / (4 * G)   
where G = 6. 67E-11 in SI units.
    V = (PI / 6) * D3
  rho = M / V = (3 * ag) / (2 * PI * G * D)


Mars: rho = (3 * 0. 38 * 9. 81) / (2 * PI * 6. 67E-11 * 6. 8E6) = 3. 9 g/cm3.
Tau Ceti VII: rho = (3 * 0. 91 * 9. 81) / (2 * PI * 6. 67E-11 * 29E6) = 2. 2 g/cm3.

Note that the gravity isn't actually the same as Mars (0. 91 Gs vs 0. 38 Gs), but if it were the density would still be a comfortable 0. 92 g/cm3.

You can also check the density in SM mode by selecting the body and clocking the "Modify Body" button in the lower-right panel.  I'm fairly sure this density is used to compute the gravity, not vice-versa, so you can be assured that the range of values is reasonably realistic.   ;)

You're right, I was meaning Venus and typing too late at night.  And its density is indeed . 4 of Earth's, which is 2. 2g/cm3 as you say.  I think I was just thrown off a bit by the 62b max population, which is about three times higher than the next largest I've seen, at a lower gravity than Earth's.