Facts/Science Supporting This:
The size of the Earth is just right! If it were a little less massive, it could not hold onto its atmosphere and oceans. If it were a little more massive, its greater gravity would make it much harder to leave Earth. This would make space exploration much more difficult and probably not practical.
All of Earth’s space exploration so far has been done using chemical rockets, but we have gone about as far and fast as we can go using these fuels. To continue into deep space exploration, we will need to move beyond chemical fueled rockets to nuclear powered rockets. These all use the element U-235 at some point in their fuels production. This element is very rare in the Universe. Strangely enough though, the Earth is super enriched with U-235, making advanced space exploration possible for the human race.
If the human race were located on Jupiter or any of the other gas-giant planets, space flight would be impossible because current chemical rockets are right at the edge of their maximum theoretical efficiency and couldn’t go fast enough to achieve escape velocity. Even if the current liquid oxygen and hydrogen fuel were used to power a space craft made of the lightest materials available and conceivable, it is almost impossible to move beyond the 95% fuel to 5% rocket weight limit, making deep space flight possibilities very limited.
Chemical rockets can be supplemented somewhat with air launches or rail gun launches, but farther and faster space travel will require nuclear rockets but because the Earth is super enriched with U-235, nuclear rockets are possible for humanity. These types of rockets are currently in the experimental stage.
Go to the Source:
“The Tyranny of the Rocket Equation” www.nasa.gov/mission_pages/station/expeditions/expedition30/tyranny.html