Final answer:
A rocket is the only vehicle suitable for space travel due to its ability to function effectively in the vacuum of space, where there is little to no atmospheric resistance and no air to provide thrust. Rockets can attain high speeds needed to escape Earth's gravity.
Step-by-step explanation:
The reason a rocket is the only thing that can travel in space is primarily due to the efficiency of rockets in the vacuum of space. Unlike in Earth's atmosphere where air creates resistance and does not provide any thrust, rockets are far more efficient in outer space where there is almost no air resistance. Additionally, rockets can achieve the high speeds required to escape Earth's gravity, hop between continents, or enter orbit. Airplanes can assist in the launch process by providing an initial velocity and reducing atmospheric resistance, but only rockets can continue into space.
Space travel is far from being a trivial solution for Earth's problems, as it is both energetically and economically costly. However, for actual space travel, rockets are indeed the most suitable vehicles because of their capability to function in the absence of air, withstand the vacuum of space, and provide massive thrust to overcome Earth's gravitational pull.