Where does interstellar space begin?

Going by its name, it might be easy to guess where interstellar space exists – ‘Inter’ means in between, and ‘Stellar’ refers to stars. This would mean interstellar space is that part of space that exists between stars. However, that is not true.

Bye, bye heliosphere, hello interstellar

Interstellar space begins where the Sun’s constant flow of material and magnetic field stops affecting its surroundings. This place is called the heliopause.

The heliopause marks the end of the heliosphere, the region created by our Sun. the heliosphere, which is like a bubble, is created by the Sun sending a constant flow of particles and a magnetic field out into space at over 6,70,000 miles per hour. This stream of particles sent out by the Sun is called solar wind.

Like the wind on Earth, the solar wind pushes against any particles around it. This means the solar wind is constantly pushing against particles from other stars. The heliosphere exists till such a place where the solar wind can keep the foreign particles out. After this place, the interstellar space begins.

How do we know if we are in interstellar space?

Well, clearly defined boundaries for space are mentioned in paper, but it can’t really be seen with the naked eye. Interstellar space cannot be experienced on Earth. So far only probes sent by NASA have been able to identify interstellar space.

The probes would help us know we are in interstellar space when there is an increase in ‘cold’ particles around them. This is because, inside the heliosphere, the solar particles are hot but less concentrated. Outside the heliosphere, the particles are highly concentrated but are much colder.

The probes would also know they are in interstellar space when they identify a magnetic field that does not originate from our Sun.

Two probes sent by NASA – Voyager 1 and Voyager 2 – are the only ones to reach interstellar space.


Picture Credit : Google