Is the Earth's net charge really zero?

[username]

My physics book says that the Earth has a net charge of zero. How is this possible with all those particles coming in from the sun etc, I would of thought it would accumulate a charge somehow.

 

[mathman]

Which particles? Most of what comes from the sun is neutral (photons anf neutrinos). I would guess that there are enough positive and negative charged particles to cancel out.

 

[username]

Well what if you charged something up then shot it out into space, then the Earth would have a net charge but maybe charge from the atmosphere would replace it?

 

[Iron Sun X]

If the Earth gained a charge it would necessarily attract particles of the opposite charge and repulse particles of like charge and the charge would return to neutral. In reality, I'm sure the Earth can and does carry a small charge but it isn't constant and is negligible compared to the mass of the Earth.

 

[Nereid]

If you think of the inter-planetary medium (the stuff between blobs like the Sun, planets, moons, asteroids, etc) as a plasma, you'll see that any net charge which any such blob had would be temporary (as Iron Sun X said).

Of course, as you explore the details ever more finely, you will find plenty of 'exceptions' to this 'no net charge' rule, including and especially that to an astronomer, 'temporary' can be a long time!

 

[niketkp]

Because electrons move faster than ions in most neutral plasmas, anybody immersed in the plasma will tend to pick up a negative charge, especially if it is cooler than the plasma. The plasma temperature at the Earth's orbit is of the order of 100000K.

So, the Earth has to have a net negative charge of a certain amount. Is it appreciable - I don't know.

The Earth, not counting the atmosphere, definitely does have an electric charge. This charge produces an average vertical electric field of about 100V/m at the Earth's surface. But that mostly ends at the ionosphere. So given the Earth's size, the solid and liquid part of the Earth has around 400000 Coulombs of charge.

Going back to the second paragraph, there will be region of the plasma that has net positive charge that balances out the net negative charge over very long distances. So part of the problem is deciding how much of the plasma you count as "part of the Earth".