Could a planet larger than earth with half the gravity have a denser atmosphere?

I want to create a world that abides completely by our understanding of reality. The whole premise is that "If the Universe is large enough, this would all be non-fiction", assuming the laws of physics are constant everywhere. It absolutely must be 100% scrutiny-proof.

Firstly, the planet is designed to be a sort of superficial "Parallel Earth". However, the actual workings of the planet and its species can be adapted as needed. The planet will have large amounts of gigantism (pun intended). The planet will include human-like natives; ray-like whales that are 60-80m long; 'Sauropods' on par with the largest titanosaurs. But the most limiting factor is having theropod-like dragons (technically wyverns), preferably upwards of 10m in length.

I've plugged some numbers into various calculations and I've settled on the following properties:

Surface Area: 602,000,000km2 (18% larger than Earth)
Radius: 6.923.5km (8.5% larger than Earth)
Mass: 3.524*10^24kg (41% less than Earth I *think*)
Volume: 1,390,160,000,000km3 (28% larger than Earth)
Gravity: 4.9m/s/s (Half of Earth)
Density: 2.83g/cm3 (54% less than Earth)

With the atmospheric density 6x higher than Earth (around 7.2kg/m3) this gives an 850kg limit of flight if the 70kg Argentavis is used as a maximum, or a 2400kg if the Quetzalcoatlus is used as a limit. I originally had it at 3x Earth's.

Would these figures yield a stable planet?

Would the mass of the planet have a large enough magnetic field to hold such an atmosphere? Could I increase the atmospheric density to 12x Earths or higher? What sort of atmospheric composition would it need? How would I achieve a planet with the right conditions and parameters if this isn't stable?

The larger surface area allows more room for life (and thus giant life), whilst having larger oceans to support a denser atmosphere. A higher level of volcanic activity would also be included.

I did intend for it to be a binary planet as well, but all these kinds of things can be changed.

posted almost 8 years ago

Zac Walton‭

1 reputation 4 0 0 0