The terms "outer space" and "deep space" are often used interchangeably,

but there is a subtle difference between the two. 

Outer space refers to the region of space that is beyond the Earth's atmosphere. 

Deep space, on the other hand, refers to 

the region of space that is beyond the Solar System. 

The boundary between outer space and deep space is not well-defined, but it is 

generally considered to be the distance at which the Sun's gravity is no longer dominant. 

This distance is about 1 light-year, or about 63,241 astronomical units. 

Outer space is a relatively well-studied region.  

Scientists have sent numerous spacecraft into outer space to study the Sun, the planets, and the moons. 

They have also sent spacecraft to study the asteroids and comets that orbit the Sun.