# Does gravity affect radiation incident on the planet?

Just curious ...

Known facts:

• When outside the atmosphere levels of radiation are higher

Question:

If the matter of the atmosphere and magnetosphere as shields is kept aside for a moment, does gravity affect radiation incident on the planet?

Considering a barren planet (without an atmosphere), I'd say yes - For the same size, a planet of greater mass would have more incident radiation, because the gravity well it created would be deeper.

• That's what I thought too. Incidentally, the link to you vworker profile looks broken. Sep 5 '13 at 5:35
• @Everyone, the link has now been re-routed to the correct url. vWorker changes its url scheme every so often :P Sep 5 '13 at 5:44

The energy of the particles in the solar wind is well above the escape velocity of the Earth. The escape velocity of a proton from the Earth's surface corresponds to an energy of about an electron volt, and the particles in the solar wind have energies 1,000 to 10,000 times higher than this. So the gravity of the Earth has little effect on them.

The escape velocity from the Earth's surface is about $11,200$ m/sec. The mass of a proton is $1.67 \times 10^{-27}$kg, so the energy corresponding to escape velocity is:

\begin{align} E &= \frac{1}{2}m v^2 \\ &= 1.05 \times 10^{-19} J \\ &= 0.65 eV \end{align}

and solar wind particles have energies in the range 1 to 10 keV.

The Earth's gravity obviously has an indirect effect, because the gravity binds the atmosphere and this in turn screens out radiation. However the is little direct effect.