Is outer space a perfect vacuum?


Outer space (also called just space) is all the space in the universe beyond Earth and its atmosphere. It can be simple stated that in outer space there is no air (atmosphere) and it is a vacuum (empty of matter) however, it is not actually empty. Space contains tiny particles called cosmic dust and elements like hydrogen and helium atoms. The vastness of space not having any beginning or end, has unimaginable distances between stars, planets and galaxies where the gas molecules density is so low that it is practically nonexistent. This is why astronauts have to wear special suits carrying air (oxygen) supply for breathing. Therefore, having a few hydrogen and helium atoms for every cubic meter (or per cubic centimeter) space is virtually a vacuum. The gravitational force of the attraction of large bodies (such as planets and stars) also cause gas molecules in space to pull closer to their surfaces thus, leaving the space between them virtually empty.

Hence outer space, is not a total vacuum or perfect vacuum but rather has the density and pressure of an almost perfect vacuum. A perfect vacuum has a gaseous pressure of absolute zero which in reality, does not exist. A perfect man-made vacuum has never been obtained and the most nearly perfect vacuum that exists, is in outer space where on an average it contains less than one molecule per cubic meter.