In astronomy and for the distinction between aviation and space travel, space or cosmic space is the part of the universe more than 100 kilometers from Earth. This boundary is the Kármán line, although it is not a line, but a spherical surface. There is still debate whether an altitude of 80 kilometers no longer meets relevant physical criteria. Deep space is the part of the universe at a greater distance than the Earth-Moon lagrange points, well further than the Moon.
Space is not a true vacuum, but consists mainly of hydrogen and helium plasma, electromagnetic radiation (particularly cosmic microwave background radiation) and neutrinos. Space contains very few atoms of other elements (metals) and dust particles. Intergalactic space contains only a few hydrogen atoms per cubic centimeter (inhaled air contains about 1019 atoms per cubic centimeter). According to most theories, space is also rich in dark energy and dark matter. Objects can also move through it, such as meteoroids and comets.
Interplanetary space is the space between the planets within the solar system. This space contains interplanetary matter - mainly cosmic rays, ionized atomic nuclei and various subatomic particles. Interplanetary space extends to the heliopause, where the heliosphere merges into interstellar space. Obviously, exoplanets have their own interplanetary space.
Interstellar space is all the space in a galaxy that is not occupied by stars and their planetary systems. The matter and radiation in interstellar space is the interstellar medium.
Two interstellar comets observed in the interplanetary space of the Solar System are Oumuamua in 2017 and 2I/Borisov in 2019.
The only man-made objects that have reached interstellar space are the Voyager 1 and Voyager 2 space probes.
Intergalactic space is the space between two galaxies, for example between the Milky Way and the Andromeda Galaxy. Because the galaxies scattered throughout the universe are very far apart, intergalactic space makes up by far the largest part of the universe itself. For example, the Milky Way is about 150,000 light-years across, while the nearest galaxy, the Andromeda Galaxy, is only about 2.2 million light-years away. According to the most accepted theory, intergalactic space will become an exponentially increasing part of the universe in the future, as the galaxies drift apart more and more. Because the intergalactic space is so large, the density within the universe is very low and so is the gravity. This allows the expansion of the universe to continue indefinitely.
In intergalactic space there is a kind of plasma, the intergalactic medium that probably consists largely of ionized hydrogen and contains exactly the same number of electrons as protons. The reason for assuming that this is an ionized gas is that the temperature is high enough to allow bound electrons in a hydrogen nucleus to escape. The density of the intergalactic medium is estimated to be 10 to 100 times the average density of the universe. Studies show that the intergalactic medium can be observed and explains much of the universe's missing matter.