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/m^{3}. For comparison, pumice has a density of 0. 25 g/m^{3}. 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/cm

^{3} which seems reasonable. Mars is 3.9 g/cm

^{3} for comparison.

Quick maths:

M = (a_{g} * D^{2}) / (4 * G) where G = 6.67E-11 in SI units.

V = (PI / 6) * D^{3}

rho = M / V = (3 * a_{g}) / (2 * PI * G * D)

Mars: rho = (3 * 0.38 * 9.81) / (2 * PI * 6.67E-11 * 6.8E6) = 3.9 g/cm

^{3}.

Tau Ceti VII: rho = (3 * 0.91 * 9.81) / (2 * PI * 6.67E-11 * 29E6) = 2.2 g/cm

^{3}.

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/cm

^{3}.

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.