The reason there is no sound in space is primarily due to the absence of a medium for sound waves to travel through. In Earth's atmosphere, sound is transmitted as a series of compression waves that require molecules, such as air or water, to propagate. When sound is generated, it causes vibrations in these molecules, which then travel as waves and reach our ears, allowing us to perceive sound.
However, in the vacuum of space, there are very few molecules or particles to transmit these vibrations. Without a medium to carry the sound waves, they cannot propagate, and thus, sound cannot be heard. Space is essentially empty, and the molecules that exist are so widely dispersed that they cannot effectively transmit sound waves.
If someone were to hear a sound while being outside Earth's atmosphere, it would indicate that they are not in the true vacuum of space but rather in an environment that contains a medium capable of transmitting sound waves. For instance, if they were inside a spacecraft or wearing a spacesuit equipped with an air supply, they could potentially hear sounds generated within that enclosed environment. However, in the vast expanse of space itself, sound cannot be heard due to the absence of a medium for its transmission.