Posted on August 25, 2019
There is no boundary line in space.
There's no "Welcome to Interstellar Space" sign.
If you tried to define "interstellar space" as the space between stars, then ALL of space, other than those portions taken up by stars, would be counted as interstellar space. Like even the bit of space you are sitting or standing or lying down on.
That's not how we use the term.
No, scientists define interstellar space as the place where the Sun's constant flow of ions - something called the solar wind - AND the Sun's magnetic field both stop affecting the surroundings. And even though that defined boundary is invisible to our eyes, it has a special name: the heliopause.
(You probably know that helio- means Sun.)
Since the Sun is a sphere, and it emits ions in every direction, we call the sphere in which the solar wind and the Sun's magnetic field affects space the heliosphere.
If you were ever to reach interstellar space in a well-equipped spaceship, you would find that there you could detect many more particles around you, more than inside the heliosphere - but you'd also discover that the particles were very much colder. You'd be able to detect magnetic fields that don't originate from the Sun, and interstellar winds rather than the solar wind!
On this date in 2012, Voyager 1 became the first human-made object to enter interstellar space! (It took it almost 35 years to get there!)
I knew that the farthest reaches of the solar system, way beyond the heliopause, is the spherical "shell" of icy bodies called the Oort Cloud.
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| Notice that this is not an ordinary to-scale diagram; it's an exponential scale. |
Check out how long it will take Voyager 1 to get to, and then to get through, the Oort Cloud:
- Voyager 1 will reach the beginning of the Oort Cloud around 300 years from now.
- And it will reach the end of the Oort cloud in 30,000 years!!!
- And in 40,000 years, the spacecraft will finally be closer to another star than to our Sun!
Wow.
Mind blown!
Also on this date:
Anniversary of the liberation of Paris
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