Our planet is surrounded by a wispy-thin layer of gas that keeps us warm and allows weather
to happen and basically makes all of life on Earth possible.
Except... that precious atmosphere of ours is actually leaking, every second, into outer
space.
Luckily, it's a really slow leak, since for any object--be it a molecule of gas, a rocket,
or a cat -- to break the tether of Earth's gravity and escape, it has to hightail it
out of here at 34 times the speed of sound.
It takes the energy of a metric tonne of TNT to boost a person to that speed, and less
energy for lighter objects: 1/10th of that for a cat, for example.
Barring a large asteroid impact that can eject large swaths of atmosphere into space, the
only gases that regularly escape Earth's atmosphere today are Hydrogen and Helium - the lightest
elements in the universe.
There are a few ways hydrogen and helium molecules can wind up on a one-way mission to space.
Some, near the top of the atmosphere simply get enough energy from the sun's heat to escape.
Others are high-energy charged particles that would usually be stopped from escaping by
the Earth's magnetic field.
Occasionally, though, these speedy electron-lacking particles crash into a neutral molecule with
enough force to knock loose--and steal--one of its electrons.
Now neutral itself, the speeding particle is free of the earth's magnetic field, and
if the collision happens to set it on a course for the stars, that's where it goes.
Finally, some of Earth's magnetic field lines are weakened and pushed away from the earth
by the solar wind, a violent stream of plasma emanating from our sun.
Charged particles guided by these magnetic fields can simply fly off the weak ends like
sparks off a live wire.
But if our planet didn't have a magnetic field at all, things could be a lot worse.
Mars, for example, has no protective magnetic field, and so what little atmosphere it has
is constantly buffeted and ripped away by the solar wind.
Even with its protective bubble, Earth is losing enough hydrogen to fill a meter-wide
balloon every second.
No need to worry - it'll take a few billion years before we lose all of our hydrogen this
way, but maybe sometime in the distant future, someone will look at Earth and ask, just as
we do of Mars now: Was there ever life on this chunk of rock?