Solar radiation and Earth orbit

[alpha2cen]

We know well the Sun emits solar wind and solar rays.

And, the Earth is attracted by Sun's gravity.

If there were no solar radiation, how much Earth orbit around the Sun would be changed?

Are there any equations?

Edited February 6, 2011 by alpha2cen

[insane_alien]

not much, the solar wind and radiation pressure doesn't exhert much force on the earth.

 

iirc its about 1.5*10^8 N. sounds like a lot right? but the mass of earth is so stupendously larger than that it doesn't make much acceleration 7.7×10^-17m/s^2 to be exact.

 

you undergo more acceleration when you fart while riding an exercise bike.

 

so the result is that the earths orbit would be stable a few nanometers closer to the sun. i could work out exactly how much closer but whats the point? its so close to zero that it effectively IS zero.

[D H]

not much, the solar wind and radiation pressure doesn't exhert much force on the earth.

 

iirc its about 1.5*10^8 N. sounds like a lot right?

That's small by a factor of four or so, but regardless the net effect on the Earth is exceedingly small. The effect on a small object is not so small. There are several competing effects here.

 

The solar wind is essentially a non-player except for extremely small objects; nano dust or beta meteoroids. For these extremely small objects solar wind dominates over radiation effects. The solar wind carries these tiny, tiny objects out of the solar system.

 

Solar radiation pressure has a radial and tangential component. The radial component doesn't do much at all. The net sum of the radial component of radiation pressure and gravitational acceleration is still a 1/r² central force. It is the tangential component that causes an object to spiral in or spiral out.

 

By way of analogy, imagine that you are driving one of those old, old cars with vertical windshields, and it starts raining vertically. Little if any rain will hit the windshield while the car is not moving. Because the rain falls with a finite speed, the windshield will start getting rained upon once you start moving forward. A similar phenomenon, called the aberration of light, happens to an orbiting object. From the perspective of the object, the light from the Sun appears to be coming slightly in front. If the object re-radiates the incoming radiation uniformly in all directions, the net result will be to make the object lose angular momentum -- i.e. to spiral in toward the Sun. This is the Poynting-Robertson effect. Small objects slowly spiral in toward the Sun, up to the point where solar radiation heats them to the extent that they disintegrate. Then the solar wind carries the disintegrated particles out of the solar system.

 

That "if" above (if the object re-radiables the incoming radiation uniformly in all directions) is a reasonable assumption for small objects, not so good for not so small objects. For example, the dawn side of the Earth is cooler than the evening side, so the net outgoing radiation is opposite the Earth's velocity vector. This is the Yarkovsky effect. The effect on objects with a prograde rotation is to make them spiral out. Objects with a retrograde rotation spiral in due to the Yarkovsky effect.