A rock from Mars experiences a 263% increase in its weight once it arrives on Earth. What accounts for this increase in weight?

The mass of Mars is smaller than that the mass of Earth, therefore the acceleration of gravity on Mars is much less than that the acceleration of gravity of the Earth.

The weight of an object is directly proportional to the magnitude of the gravitational acceleration of the planet where it is.

In this case, the gravitational acceleration in Mars is 3.711 m/s² and that of the planet Earth is 9.807 m/s².

The acceleration of gravity on Earth is 2.63 times greater than that the acceleration of gravity on Mars. This explains that the same object weighs 263% more on earth