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Fraser
2007-Mar-08, 05:16 PM
Astronomers have theorized that light from the Sun influences the speed at which asteroids spin, and now they've gathered the evidence to back it up.

Read the full blog entry (http://www.universetoday.com/2007/03/08/sunlight-puts-the-spin-on-asteroids/?1420)

justdroppedbytosaythis
2007-Mar-08, 06:40 PM
Hm... 35 million years is an awfully short period of time. If this is true, then why aren't all asteroids already spinning like crazy?

01101001
2007-Mar-08, 07:01 PM
Hm... 35 million years is an awfully short period of time. If this is true, then why aren't all asteroids already spinning like crazy?

From the ESO press release (http://www.eso.org/outreach/press-rel/pr-2007/pr-11-07.html), the effect changes rotation rates, either up or down.

And, I'd presume, it might change rates in different directions over time.


Although this is an almost immeasurably weak force, its effect over millions of years is far from negligible. Astronomers believe the YORP effect may be responsible for spinning some asteroids up so fast that they break apart, perhaps leading to the formation of double asteroids. Others may be slowed down so that they take many days to complete a full turn.

John Mendenhall
2007-Mar-08, 08:13 PM
Hm... 35 million years is an awfully short period of time. If this is true, then why aren't all asteroids already spinning like crazy?

And the effect will be much less at greater distances from the sun, and with increasing asteroid mass. Mass goes up as the cube of the asteroid radius, the flat plate area exposed to the sun as the square of the radius . . .

But - what is this effect like around a really hot star? Or a binary?

Jerry
2007-Mar-09, 02:16 PM
They seem to imply that this is due to radiation pressure, but isn't the primary force solar wind cations?

01101001
2007-Mar-09, 05:55 PM
They seem to imply that this is due to radiation pressure, but isn't the primary force solar wind cations?

From the ESO press release (http://www.eso.org/outreach/press-rel/pr-2007/pr-11-07.html):


"The warming caused by sunlight hitting the surfaces of asteroids and meteoroids leads to a gentle recoil effect as the heat is released," he added. "By analogy, if one were to shine light on a propeller over a long enough period, it would start spinning."

Cations... Cations... Nope.

Wikipedia: YORP Effect (http://en.wikipedia.org/wiki/Yarkovsky-O'Keefe-Radzievskii-Paddack_effect)


Imagine a rotating spherical asteroid with two wedges attached to its equator. The reaction force from photons departing from any given surface element of the sphere will be normal to the surface, such that no torque is produced. Energy reradiated from the wedges, however, can produce a torque because the wedge faces are not parallel to the sphere's surface. An object with some "windmill" asymmetry can therefore be subjected to minuscule torque forces that will tend to spin it up or down as well as make its axis of rotation precess.

Cations... Cations... Nope.

Introductory material seems to disagree with you. Do you have a cite from the literature that the YORP effect is not from sunlight but from solar wind cations?

iantresman
2007-Mar-09, 06:29 PM
From the ESO press release (http://www.eso.org/outreach/press-rel/pr-2007/pr-11-07.html):
Cations... Cations... Nope. [..] Introductory material seems to disagree with you. Do you have a cite from the literature that the YORP effect is not from sunlight but from solar wind cations?

I don't think Jerry is suggesting that the YORP effect is due to solar wind ions, only that there should be an affect due to the impact of solar wind ions.

For example, the solar wind pressure is strong enough to blow some of Earth's atmosphere into space [ref (http://science.nasa.gov/newhome/headlines/ast08dec98_1.htm)]. So it would be interesting to compare the two effects.

And charging by the solar wind of the dark side of the Moon [ref (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2007GeoRL..3402111H&db_key=AST&d ata_type=HTML&format=&high=45cce9d73302099)] appears to have a similar effect to charging due to the photoelectric effect is able to levitate lunar dust up to 60cm high [ref (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1978LPSC....9.3225P&db_key=AST&d ata_type=HTML&format=&high=45cce9d73331779)] (with an opposite force on the lunar surface).

The force of the solar wind is certainly significant on dust and grains [ref (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1964ApJ...139..951P&db_key=AST&d ata_type=HTML&format=&high=45cce9d73305230)].

Argos
2007-Mar-09, 06:34 PM
I don't think Jerry is suggesting that the YORP effect is due to solar wind ions, only that there should be an affect due to the impact of solar wind ions.

For example, the solar wind pressure is strong enough to blow some of Earth's atmosphere into space

... on account of the magnetic field.

John Mendenhall
2007-Mar-09, 09:19 PM
... on account of the magnetic field.

What?

Argos
2007-Mar-10, 01:45 PM
I mean, maybe its not a good idea to use Earth in comparison with an asteroid on account of its magnetic field.

iantresman
2007-Mar-10, 03:05 PM
I mean, maybe its not a good idea to use Earth in comparison with an asteroid on account of its magnetic field.

How about erosion of the Martian atmosphere by the same mechanism? [Ref (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1992JGR....97.3159P&db_key=AST&d ata_type=HTML&format=&high=45cce9d73312408)]

I think all this begs the question, what is the relative effect of (a) photons (light) (b) solar wind pressure (c) solar wind charging (d) photoelectric effect charging, on particles and solid objects.

The closest I've found is the "momentum equation" for particles moving in a plasma which notes that gravity is the dominant force for particles larger than grains (but electromagnetic forces are stronger for grains and smaller). It also includes a term for radiation pressure (and other forces) which I think accounts for the affect of photons. See Dusty plasma (http://www.plasma-universe.com/index.php/Dusty_plasma) (on my own Web site).

Argos
2007-Mar-12, 01:09 PM
How about erosion of the Martian atmosphere by the same mechanism?

Yeah, that would be ok. In fact I was about to suggest it.

John Mendenhall
2007-Mar-12, 03:11 PM
I mean, maybe its not a good idea to use Earth in comparison with an asteroid on account of its magnetic field.

True.

I've often thought that it should be possible, knowing the mass of a planet, the composition of the atmosphere, the average temperature, and the magnetic field, to calculate whether or not a planet can retain an atmospere. The obvious application is to see if it is worthwhile to try and produce an atmosphere for Mars. My guess is no, but it's a guess.

And I forgot to mention outgassing, and biological activity.

Jerry
2007-Mar-12, 03:35 PM
I don't think Jerry is suggesting that the YORP effect is due to solar wind ions, only that there should be an affect due to the impact of solar wind ions.

For example, the solar wind pressure is strong enough to blow some of Earth's atmosphere into space [ref (http://science.nasa.gov/newhome/headlines/ast08dec98_1.htm)]. So it would be interesting to compare the two effects.

And charging by the solar wind of the dark side of the Moon [ref (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2007GeoRL..3402111H&db_key=AST&d ata_type=HTML&format=&high=45cce9d73302099)] appears to have a similar effect to charging due to the photoelectric effect is able to levitate lunar dust up to 60cm high [ref (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1978LPSC....9.3225P&db_key=AST&d ata_type=HTML&format=&high=45cce9d73331779)] (with an opposite force on the lunar surface).

The force of the solar wind is certainly significant on dust and grains [ref (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1964ApJ...139..951P&db_key=AST&d ata_type=HTML&format=&high=45cce9d73305230)].

I would expect solar wind particles colliding with an asteroid to put a differential physical load on the asteriod that would behave exactly like the photon loading...I would also expect this particle force to be much greater than radiation pressure - whether or not the particles are ionized.

Therefore, I do not understand how the radiation pressure could be measured without some method of subtracting out the effect of the solar wind. None of this is mentioned in the article - am I missing something, or is the ESA?

Nick4
2007-Jun-07, 05:02 AM
Makes scence the sun acts as a wind working much like solar sailes only the astroide is the solar sail.