Magnetic Field Springing a Leak in Earth's Air Supply

The scoop: Earth's atmosphere is slowly leaking out into space. Now that a group of Swedish scientists think they have finally figured out how, should we be worried about running out of air any time soon?

Dave on Earth (1:59 PM) Hi, is this Hans? This is Dave Mosher from Discovery Space.

Atmosphere Hunter (1:59 PM) Hi Dave, yes it's me.

Dave on Earth (1:59 PM) Most excellent -- thanks for taking the time to chat with me.
Are you at the office? Home? Somewhere else?

Atmosphere Hunter (2:00 PM) I'm at home.
Oh, I just got a telephone call -- sorry, I'll have to leave for a minute.

Dave on Earth (2:00 PM) No problem.

Atmosphere Hunter (2:02 PM) Ok, now I'm back!

Dave on Earth (2:02 PM) Great. So, you study the atmosphere -- from where?

Atmosphere Hunter (2:04 PM) I'm working at the Swedish Institute of Space Physics in Kiruna.
Kiruna is in the far north of Sweden, well above the Polar Circle.
It's autumn here now, the leaves are turning color, and the temperature is 40 to 50 degrees Fahrenheit.

Dave on Earth (2:06 PM) Pardon the pun, but it sounds like a cool place.
But what is a space physics institute doing above the Polar Circle?

Atmosphere Hunter (2:07 PM) It was established in 1957 (during the International Polar Year), mainly to study the aurora.
We also have a rocket range where they launch sounding rockets and balloons.
As for me, I'm studying the Earth's atmosphere both at low- and high-altitude, as well as the magnetosphere of the planet.

Dave on Earth (2:08 PM) Wait... rockets?

Atmosphere Hunter (2:09 PM) Yes. They have discussed launching tourist space flights from Kiruna -- the benefit would be that the tourists would get a chance to see the aurora from space

Dave on Earth (2:09 PM) Very cool indeed.
Now, you recently put out a paper stating that Earth is slowly leaking its atmosphere to space. What gives?

Atmosphere Hunter (2:11 PM) Yes, but that's not a new result itself.
I think a paper from 1972 first showed that a lot of ions (charged particles) in space around the Earth come from its atmosphere -- not from the solar wind.
Even before that, however, someone suggested that Earth could be magnetically connected to the solar wind. Important, because such a connection makes the escape of the atmosphere easier.

Dave on Earth (2:13 PM) This is a pretty "Newtonian" question, but how does the Earth keep its precious atmosphere from leaking into space?

Atmosphere Hunter (2:14 PM) The short answer is gravity, but that's a great question.
To overcome gravity, atmospheric atoms/molecules need enough energy to reach an escape velocity of about 25,000 mph.
That's fast, but ions can achieve incredibly high energies by encountering electric and magnetic fields.

Dave on Earth (2:16 PM) Let's backtrack a moment -- where do we get ionized gas from in the first place?

Atmosphere Hunter (2:18 PM) The sun's "extreme" ultraviolet light has enough energy to knock electrons off of atmospheric gas atoms, turning them into charged particles (from a neutral state, of course).
Those electrons can stream along magnetic field lines, hit the atmosphere and cause both ionization and light -- the aurora.
Also, it's difficult for charged particles to move across magnetic fields.
But it's easy for them to move along magnetic fields.

Dave on Earth (2:24 PM) I'm guessing it'd be very hard to lose atmosphere near the equator, since the magnetosphere originates from the poles?

Atmosphere Hunter (2:24 PM) Yes -- and that's precisely why we are looking for loss in the polar regions.

Dave on Earth (2:24 PM) What have you discovered so far?

Atmosphere Hunter (2:25 PM) We found that there's much stronger acceleration of ions at the polar cap region at a high-altitude than we thought.
We were also able to pinpoint and understand one of the main acceleration mechanisms: so-called "centrifugal acceleration."

Dave on Earth (2:26 PM) Pretend I'm 10 years old -- how do you describe "centrifugal acceleration" to me?

Atmosphere Hunter (2:27 PM) Centrifugal acceleration is like a sling shot effect.
Think of gas ions as weights attached to a string (the magnetic field line), which the weights can slide along pretty easily.
Well, those strings are moving across the polar cap, from the day side toward the night side...
And the magnetic field lines of Earth are bending a bit towards the day side, and away from the night side.
So you're more or less swinging the strings with sliding weights on them -- and the weights will start to move outward.
The faster you swing it, the faster the weights move. And if the line is straight enough, they fling into space!
What do you think about that explanation?

Dave on Earth (2:31 PM) Makes sense to me. How did you study it, though?

Atmosphere Hunter (2:33 PM) The Cluster 4 spacecraft mission, which is a constellation of four identical spacecraft flying in a formation around the Earth. That allows you to measure all kinds of things you can't with one spacecraft.
In our case, the magnetic field.

Dave on Earth (2:37 PM) Sort of gives you magnetic "depth perception" then...

Atmosphere Hunter (2:37 PM) Yes.
The acceleration we observed means that the ions leak out into the solar wind -- that's the most likely fate, at least.

Dave on Earth (2:39 PM) What's another option?

Atmosphere Hunter (2:41 PM) The magnetic field lines close before the ions manage to escape -- so they can be recycled, in a way.
So you have magnetism and gravity holding in the atmosphere.

Dave on Earth (2:42 PM) How much gas is flung out into space, though?