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Q & A: Hydrogen in Sun and Earth atmosphere?

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Most recent answer: 06/01/2011
Q:
Hydrogen is in abundance around the sun but not on the earth.Why?
- Dinesh Vodela (age 15)
Hyderabad,AndhraPradesh,India
A:
In the early days of the earth, several billion years ago, there was probably lots of hydrogen in the atmosphere.  But hydrogen can be lost into space if its velocity is big enough.   The escape velocity of a particle is proportional to (MG/R)1/2 where M is the mass, G is Newton's constant and R is the radius.   The velocity of a gas particle due to thermal motion is proportional to (kT)1/2 where k is Boltzman's constant and T is the temperature.   When the thermal velocity exceeds that of the escape velocity, the particle can easily escape.  Putting in the masses, radii, and temperature of the earth and sun you can find there is an overall ratio of more than a hundred.  Hydrogen would rather stick around the sun, not the earth.

LeeH

Not to mention, the hydrogen that does stick around here is cool enough to bind into compounds that stick even better, such as water. /mw

(published on 06/01/2011)

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