We grow crops (plants) on earth, so it's very important for that to go beyond earth because if there is no way to grow crops, we won't get enough nutrients from some synthetic (fake) food. hope I helped! :)
The problem of the "sound barrier" has to do with moving through
air, and the things the air does when you try to push it out of the
way faster than the speed of sound. Moving through air faster
than sound was an engineering and technological problem, not
a scientific one.
Concerning light, that's about 874 thousand times faster.
See the problem ?
Any electromagnetic wave, like light or heat.
The frequency of the wave has not changed.
In fact, the frequency of a wave is given by:
where v is the wave's speed and 
is the wavelength.
Applying the formula:
- In air, the frequency of the wave is:
- underwater, the frequency of the wave is:
So, the frequency has not changed.
From p1v1/t1 = p2v2/t2
pressure unchanged ... cancelled out
v1=605 , t1=27C = 300K,
t2=-3C = 270K
***remember temperature must be in Kelvin
we got
605/300 = v2/270
v2 = 545
