You know that sound needs a medium to travel. The speed of a sound wave depends upon the medium through which it travels. In general, sound travels faster through solids than through liquids or gases. Before we see if we can hear in space, let us first discuss about the objects found in space. Space contains stars, planets, comets, moons asteroids and few other cosmic bodies. You might have learned that space is a vacuum. So how can space contain all these massive bodies and still be a vacuum?
It's because space is big. Between these large objects are millions of miles of emptiness. This empty space called interstellar space is practically devoid of all matter, so it's effectively a vacuum. Now, sound waves need a medium to travel. As there's almost no matter in interstellar space, sound can't travel through it.
So how do astronauts outside their space shuttle talk to each other? It is because of the space suit that contains a radio unit. Radio waves are electromagnetic waves that can travel through vacuum. Radio unit transmits and receives signal, converts it into sound which will travel through the air in the space suit.
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