How do we know what the level of gravity is on other planets without having been there and/or landed rovers.
In: Earth Science
Gravity is a force two massive objects exert on each other (yes you also pull the earth towards you it’s just that the earth is roughly 10²³ times, read a 1 with 23 zeros, heavier and thus it’s pull is A LOT stronger than yours). This is true for large and small objects though it’s a rather weak force if you consider how massive the earth is and how you could still jump.
As a formula gravity is given by F = – gamma * m*M /r²
F is the force (gravity), gamma is a constant value that you can calculate once and that stays the same no matter the objects you’re comparing. Small m is the mass of the small object, and large M the mass of the bigger object and r is the distance between the two, it’s called r for radius, because the force works in all directions hence points on a circle with the same distance towards the center of mass experience an equal amount of force, but as we just look at one object it’s basically the distance between the two centers of mass. Oh and the minus sign is just there as a direction, in that case it’s an attractive force that pulls towards instead of pushing away (positive sign).
So what you could do is just look at the trajectory of the planet compared to other huge objects of known mass and distance, like the sun or one of it’s moons and so on. If you know one of these masses and the force you can calculate the other mass.
And so if you have the mass of that planet you essentially assume the center of mass if at the core of the planet (sounds reasonable for a ball shaped object), making r the distance between the core and it’s surface or the radius of that ball. The mass of your object (in that case the rover can be measured on earth). And so you got all you need.
Now as the rover is mostly staying on the surface and as the planet is likely not gaining or losing mass, you can also do what we do with the formula on earth and simplify it by putting gamma, M/r² all in one new constant called **g** and simply say F = m*g. And then you compare g_earth to g_mars for example and you can say how bigger or smaller it is.
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