Gravitational Anomaly?

[Major Klutz]

Ran across this a few nights ago. Usually don't pay close attention to the details but this one caught my eye because the gravity was listed as exactly 1.00G
Then I noticed the mass is 0.7954 earth masses.
How can that be? 1G would by definition mean 1 earth mass.

Spoiler

Does density have much of an effect (or any) on gravitational pull?
This planet is a bit smaller, but at ~0.89 the radius of earth and 0.79 the mass it appears to be a bit less dense than Earth.

 

[Sapyx]

Yes, the force of gravity at the surface of a planet is determined by two things: the mass of the planet, and the distance from the centre of the planet the surface is. This distance will of course vary with the density of the planet.

If a planet has exactly one earth gravity but has only eight-tenths of the mass of Earth, that must mean that the planet is smaller but denser than Earth. If you look at the stats for Earth, this bears out: Earth is 70% rock, 30% metal, and "metal" is much denser than "rock", which is in turn much denser than "ice".

As others have pointed out elsewhere, Earth's rock:metal ratio is set artificially high; the Stellar Forge can't generate Earth-like planets that exactly match both Earth's mass and gravity. Other hand-crafted planets like Taylor Colony in Tau Ceti can match, but procedurally-generated planets cannot.

 

[newman1702]

Does density have much of an effect (or any) on gravitational pull?

Density is pretty much the deciding factor. Amount of mass over area of space - if that weren't the case we'd be living in a very weird universe. Well, we wouldn't be living at all, since every point in the universe would just have the maximum possible gravity.

This is why Jupiter has some 317 or so Earth masses, but only has some 2.5g - it has low relative density, not being a solid object but rather being a ball of gas. For lots of gravity you want a lot of mass over as small an area of space as possible. This is why neutron stars have such high gravity, being the densest known objects in the universe - they can be twice the mass of our Sun while only having a radius of around 10km or so.

 

[marx]

Ran across this a few nights ago. Usually don't pay close attention to the details but this one caught my eye because the gravity was listed as exactly 1.00G
Then I noticed the mass is 0.7954 earth masses.
How can that be? 1G would by definition mean 1 earth mass.

Nope, your definition would be incorrect. To be more precise: where are you subject to 1g? Gravity also depends on your distance from the center of mass, so if you're looking at surface gravity - which is what Elite gives you - that would be the radius of the planet. However, Earth's mean radius 6,371 km, while your planet's is 5,686 km. So what would be on Earth's surface would be 685 km above Qieduia DX-K b12-0 A 1.

Now, Elite gives you the gravity at surface level on the system map. If you fly towards a landable planet, you'll notice that the g indicator will rise the closer you get. If you wish to calculate the surface gravity of the planet using the measurements Elite gives you, you can simply use Newton's law of universal gravitation. You need to adjust it to Earth masses and the result to Earth gravity, so it would look like this:

(G * (m * m_E) / ((1000 * r)^2))/g

Where G is the gravitational constant (6.674E-11 m^3/(kg*s^2) ), m is the target planet's mass, m_E is Earth's mass (5.972E+24 kg), r is the target planet's radius in km (hence the multiplication by 1000 to get meters) and g is Earth's gravity (9.81 m/s^2, or can be calculated as (G*m_E)/(r_E^2) ). That last division is so that you get your result in Earth g-s.

If you calculate this for your planet, you'll see that the result that Elite gives you is correct. But if you're looking at the surface levels of the two planets, you're comparing the gravitational pull at two different distances.

 

[Qohen Leth]

When I walk in the street, I see countless gravitational anomalies. Space should bend a little around other people's brains, but it doesn't. Oh, maybe gravity is behaving as it should then.