Yarkovsky Effect On Asteroid Detected

Henry writes "New Scientist is reporting that a JPL team has measured the recoil effect of an asteroid caused by the Sun in the process of re-emission of absorbed sunlight as heat. Astronomers believe this phenomenon, known as the Yarkovsky Effect, has brought asteroids - which are otherwise mainly located in and near the belt - towards Earth. This effect on asteroids was previously predicted, but this is the first proof."

read the explanation...

[Frennzy]

From the yarkovsky link in the article... ==== The effect of this tiny thrust on the object's orbit depends on how it spins. If the spin goes one way, Yarkovsky thrust adds to the orbital speed and the asteroid moves outward, away from the sun. If the asteroid rotates the other way, Yarkovsky thrust slows the asteroid's orbital velocity, and it draws closer to the sun.

But that isn't the question

[Tau Zero]

First, the solar wind is neutral (it has to be, otherwise the sun would build up a huge charge of the opposite sign and pull the emitted particles right back).

Second, the impact of charged particles wouldn't inherently alter a rock's orbit in a different way from uncharged particles. They'd both push in the direction of flow. The thing that makes the Yarkovsky effect work is that it depends on re-emission of particles (photons, as heat), and the direction of re-emission depends on the axis and rate of rotation.

Good question

[Tau Zero]

There probably is, because Earth is definitely warmer around sunset than around sunrise. This would mean greater IR emissions in the direction opposite the orbital motion, causing thrust in the direction of the orbit.

However, the Yarkovsky effect on Earth is going to be much smaller (probably unmeasurably small) than on a sub-kilometer asteroid for these reasons:

1. Earth's atmosphere and oceans buffer the temperature changes, leading to less variation in IR emissions per rotation and thus less net thrust.
2. While the net IR emission is proportional to the intercepted sunlight and thus the area of Earth's disc (proportional to radius squared), the acceleration is inversely proportional to the mass (which is proportional to radius cubed). On top of this, Earth is denser than typical asteroidal rocks, due to its iron core and compression of lower layers to denser mineral forms.

It would be interesting to calculate the likely influence of the Yarkovsky effect on Earth, as a high-school physics exercise (like calculating the De Broglie wavelength of a moving car). I suggest this exercise to you, for fun; if nothing else, it will give you an idea of how hard it is likely to be to measure it.