ΓΙΑΝΝΗΣ ΜΙΧΑΗΛΙΔΗΣ made an erronious assumption about designing their world.
The planet is a bit larger that Earth with it being 1.5 times more massive (by thay i mean that gravity is 1.5 g compared to Earth's 1 g) although I am not entirelly certain about it and I'm considering making it only 1.2 times more massive.
They seemed to assume that the surface gravity of their world campared to Earth's surface gravity would be directly proportional to their world's mass compared to Earth's mass.
Actually there are two gravitational factors that world builders have to calculate when designing their planets, especially the ones they want to be habitable. The surface gravity and the escape velocity.
The surface gravity determiens how fast objects fall, and how heavy people feel. The escape veloctiy determines how long the planet can retain its atmosphere before it escapes into space. The two factors don't change in the same amount when the mass, radius, volume, or average density of a planet is changed.
Earth has a radius of 6,371 kilometers, and an averge density of 5.514 grams per cubic centimeter. The surface gravity of Earth is 1 g, or an acceleration of 9.80665 meters per second per second. The escape velocity of Earth is 11.186 kilometers per second.
Here is a link to an online surface gravity calculator:
And here is a link to an online escape velocity calculator:
So we can try giving your world a mass 1.5 Earth mass while having the same radius (and thus volume) as Earth. It will have an average density 1.5 times that of Earth, or 8.271 grams per cubic centimeter.
This planet will have a surface gravity of 1.5 g, and an escape velocity of 13.7 kilometers per second, 1.2247 times that of Earth.
Now try giving your world a radius 1.5 that of Earth (or 9,556.5 Kilometers), and thus a volume 3.375 that of Earth. With 1.5 the mass of Earth of Earth in 3.375 times the volume, it will have 0.44444 the density of Earth, or 2.45 grams per cubic centimeter.
So it will have a surface gravity of 0.66 g, and an escape velocity of 11.186 kilometers per second, 1.00 times that of Earth.
Now try giving your planet the same density as Earth with 1.5 times the mass. That requires having 1.5 times the volume of Earth, and thus about 1.1447142 the radius of Earth, or 7,292.8837 kilometers.
That gives the planet a surface gravity of 1.14 g, and an escape velocity of 12.805 kilometers per second, 1.1447344times that of Earth.
In those examples, changing one factor by X amount will not change the other factors by X amount.
As a shortcut, changing the average density of a plent relative to Earth should change the surface gravity in approximately the same proportion.
As another shortcut, if you change the radius and the mass of a world by the same proportion relative to Earth, the planet will have approximately the same escape velocity as Earth.
As a third shortcut, giving a planet the same average density as Earth should change its radius and its escape velocity with approximately the same proportion.
So if you want your world to have a surface gravity of 1.5 g, you can give it the same radius and volume as Earth, with 1.5 times the mass and density.
And if you want your world to have 1.5 times the mass of Earth, of course there are many other possible volumes, surface gravities, and escape velocities for worlds with 1.5 times the mass of Earth.
If want your planet to be mostly made out of rock, with enough liquid and gas to be habitable, there are limits to its possible density range.
Many small rocky astronomical objects have very low densities, because they are made of smaller object with mergered with gentle forces and still have large vacuum spaces with them.
Your planet would be a planemo, an planetary mass object large enough to be gravitationally compressed into a spheroidal shape, for all of its internal spaces to be collapsed and filled in, for its interiod materials to be compressed to higher densitys than they have on the surface, and to have enough escape velocity to retain a substantial atmosphere, and liquid surface water.
As far as I know, there are only seven mainly rocky planemos known in our solar system. Earth has the highest average density, 5.514 grams per cubic centimeter, and the two lowest are the Moon, 3.334 grams per cubic centimeter, about 0.60464 tha tof Earth, and Europa, a moon of Jupiter with 3.103 grams per cubic centimer, 0.5627 that of Earth. And Europa has much more water proportionally than Earth, its entire surface being covered with liquid water covered by a thick ice shell with a total depth of about 100 kilometers.
There are many planemos in the other solar system, moons and dwarf planets with density lesser than the Moon. But they are either giant planets with escape velocities high enough to have vast amounts of hydrogen and helium, or objects made of mixtures of rocks and low density ices.
The highest estimated average density for any of those icey planemos is that of the dwarf planet Eris, 3.013 grams per cubic centimeter, 0.5464 that of Earth.
I think it is safe to assume that any planet or other planemo which is not entiely covered by liquid or ice but has at least some exposed solid surface area, should have an average density over 3.000 grams per cubic centimeters, and probably higher if it will be massive (and thus gravitationally compressed) enough to retain a substantial atmosphere and necessary for human breathing and for retaining liquid surface water necessary for life.
And htere are upper limits to the mass, surface gravity, escape velocity, density, etc. of worlds which are habitable for humans and beings with similar requirements in particular, and even for liquid water using lifeforms in general.