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Yarkovsky Effect On Asteroid Detected

michael posted more than 10 years ago | from the nifty-science dept.

Space 19

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."

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19 comments

hmm... (-1)

mOoZik (698544) | more than 10 years ago | (#7640917)

One would have thought the opposite would happen, that is, charged particles would directly push the object in one direction. Strange and interesting.

But that isn't the question (2, Informative)

Tau Zero (75868) | more than 10 years ago | (#7645377)

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.

read the explanation... (3, Informative)

Frennzy (730093) | more than 10 years ago | (#7640947)

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.

That damn first law... (2, Funny)

TwistedGreen (80055) | more than 10 years ago | (#7640985)

It'll mean the death of all of us.

Though the second law will probably get us far sooner.

More conclusive proof that the universe abhors life. It's just so negentropic.

This is amazing work (4, Insightful)

shweazel (583363) | more than 10 years ago | (#7641074)

These guys collected 12 years worth of data, to finally determine that an asteroid 16 million kilometers from the earth was 15 kilometers further away than calculated by the influence of gravity alone.

No wonder noone else was able to measure this till now..

Re:This is amazing work (3, Insightful)

Baron_Yam (643147) | more than 10 years ago | (#7641155)

It amazes me that the orbit could be calculated with that accuracy and precision at all... there are so many gravitational influences in the neighbourhood that I'd have thought it impossible. Anything beyond a two-body problem is a problem, right?

Re:This is amazing work (3, Insightful)

Carnildo (712617) | more than 10 years ago | (#7642950)

I think they picked an asteroid that didn't make any approaches to other large asteroids in that 16-year period. If the only objects you need to worry about are the planets, it's a lot easier to calculate, particularly for a period as short as 16 years.

It is clear... (1, Funny)

GOD_ALMIGHTY (17678) | more than 10 years ago | (#7641179)

that we must declare war and destroy the Sun immediately.

We must act now before the Moonites coerce the Sun into smashing Earth in order to gain their freedom. We cannot compete with the Moonites' large stockpiles of pr0n and Foreigner paraphernalia, and they are not below using these terrorist asteroids to destroy our way of life.

Down with the Sun. Long live Terra.

Impressive (4, Interesting)

szyzyg (7313) | more than 10 years ago | (#7641210)

But it just makes all those long term asteroid orbit simulations a little harder now, since not only do you have to know the position and velocity accurately, you now have to know it's spin and it's thermal properties. It's a great example of how orbital mechanics can be considered chaotic on reasonable timescales.

Oh since I'm here - Oblibatory link to my map of the solar system showing all the near earth asteroids.....

http://szyzyg.arm.ac.uk/~spm/ [arm.ac.uk]

Question.... (1, Interesting)

Anonymous Coward | more than 10 years ago | (#7643965)

Is there a Yarkovsky effect on the Earth as well? Why not?

Re:Question.... (2, Interesting)

GizmoDuck (137089) | more than 10 years ago | (#7644403)

My guess would be no, because the Earth's atmosphere would absorb the thrust. The particles would push directly on the mass of the asteroids, however, since very few have any atmosphere to speak of.

Good question (4, Informative)

Tau Zero (75868) | more than 10 years ago | (#7645448)

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.

Sunset where? (1)

Gothmolly (148874) | more than 10 years ago | (#7653466)

'The Earth' is warmer at sunset? Where on Earth? It's always sunset somewhere. It feels warmer where you are at sunset because the air and ground have absorbed heat all day. The effect of solar wind and the earth's rotation and all that jazz has no perceptible change. How is this +5, Informative???

Re:Sunset where? (1)

teh*fink (618609) | more than 10 years ago | (#7653577)

It's always sunset somewhere.
that's the point. reread the post and rethink your response.

Re:Sunset where? (1)

PhuCknuT (1703) | more than 10 years ago | (#7668946)

Yes, that's the whole point, it is always sunrise on the side of earth facing in the direction of earth's orbit, and sunset on the other side. Thus, the extra IR emission at the sunset side is giving earth a little extra push, always in the same direction, although it's a tiny tiny effect relative to the mass of earth, unlike some asteroids which can be much less dense.
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