Earth Causes Asteroid-Quakes

[MeteorWayne]

http://www.space.com/scienceastronomy/e ... 00120.html

Asteroids may want to think twice before they swing too close to Earth. A new study has found that our planet's gravity can cause seismic tremors, or asteroid-quakes, if the space rocks stray too close.

This process could explain why many space rocks orbiting nearby appear pristine, as if they were covered in a new and clean surface, researchers said...


The researchers observed 95 asteroids in the vicinity of our planet, called near-Earth asteroids (NEAs). They used a process called spectroscopy to determine their colors, to see if they were weathered or fresh, and then combined this data with measurements of the NEAs' orbital histories.

Of the 20 fresh, pristine-looking asteroids in their sample, each had traveled close to Earth — within the distance from the Earth to the moon — in the past 500,000 years.

"So we put two and two together and found that asteroids that come very close to the Earth have very fresh undamaged surfaces, and so something about coming close must have resurfaced them," Binzel said. "The simplest explanation is that the bodies got shaken up as they came close."

The scientists detail their results in the Jan. 21 issue of the journal Nature.

 

[Gravity_Ray]

Great reason to land some instruments (seismographs, or small automated telescopes) on the surface of these near Earth travelers and use them as eyes and ears in our solar system. Both to look at them and to look at other bodies in our solar system.

 

[3488]

Perhaps these rocks on Asteroid 25143 Itokawa were shaken up by such asteroid quakes???

The larger rocks in these views are approx 2 metres long, so we are seeing right down a only a few CM.

The tiny 540 metre x 270 metre x 210 metre sized Asteroid 25143 Itakawa seen from many differing perspectives as it roated in front of the JAZA Hayabusa spacecraft.

Andrew Brown.

 

[MeteorWayne]

I did a quick check on 25143 Itokawa, and within the last century it has no passes within 1 LD, however it is quite likely they have happened in the last 500,000 years! In 1905, ~ 6 LD, 1906 <10 LD, 1940 ~ 15 LD.
MW

 

[Mee_n_Mac]

Not to dispute the observations or the correlation to Earth passings but ...

I wouldn't have thought that the differential between near- and far- side gravity would have been large enough to do much of anything. For that small a force differential to induce much resurfacing must imply the NEOs looked at in the article are very loosely packed rubble piles ? <- note the ?, what am I missing

 

[MeteorWayne]

That's what most asteroids are!

 

[OleNewt]

Does that mean one could potentially fall into one a la outer space quicksand? Or that a kamikazi probe that we slam into the side could accidentally do a through-and-through?

 

[R1]

These things lead me to wonder if it would be a simple task to just grab gravel and cover a large, manned
spacecraft with the gravel, a few meters deep? This is provided that the spacecraft can catch up to one
flying near earth, first of all, and then match its flight to the asteroid's spin.

 

[MeteorWayne]

Does that mean one could potentially fall into one a la outer space quicksand? Or that a kamikazi probe that we slam into the side could accidentally do a through-and-through?

Well, there's not enough gravity to suck you in like quicksand. In fact, it's far more likely that if you took a step you'd launch yourself into space.

For the gravel pile type of asteroid, a fast probe might indeed punch through or shatter the object.

Of course, there are more solid asteroids. We just don't know what the percentages are because we only have accurate sizes and mass for a dozen or so. That gives you the density, so you can tell how much rock, and how much space is inside.

 

[CalliArcale]

3488, those images are STUNNING!!!! Especially that second one; it looks like we can see veins of another mineral inside some of the large boulders. It makes it all seem so much more *real* to see that.

OleNewt: one thing to remember is that the density of these asteroids, while low, is an *average* density. There are bound to be hard bits inside them. So you might punch right through. You might also go splat and lose all your momentum in the process.

 

[MeteorWayne]

http://www.space.com/scienceastronomy/e ... 00120.html


Just had a chance to read the Letter in Nature. Binzel, et al, analysed a sample of 95 earth and Mars crossing asteroids with H 14 to 20.5 (~200m-4km diameter) for which visible and NIR spectra were available to assign taxonomy.

One mystery has been the rarity of asteroids that match the most common meteorite recovered on earth, the ordinary chondrites (~ 80%). They provide a possible explanation.
Over time (about 1 million years) the surfaces of asteroids redden, and have spectra categorized as S or Sq. A fresh surface would be the Q type.

Out of the 95 asteroids in the sample, all 22 of the Q type could have had encounters with earth at less than one lunar distance during the last 500,000 years. (IOW, minimum EMOID < 1 LD during that time) The asteroids that could not have passed that close to earth within the 500,000 years were all S or Sq type.

There were also some S and Sq types that could have come close to earth, but all they could really measure was whether it was possible, not whether any particular asteroid had definately passed that close. While the EMOID was that close, the asteroid may never have been close to earth at the right time in the orbit. It's impossible to accurately integrate the precise orbit for more than a few hundred years or so. EMOID is far more predictable.
It's also possible some of those were more substantial, not the rubble piles that so many are turning out to be, and the gravitation effects of the earth weren't enough to cause seismic shaking and landslides to expose the fresh surface.

We do have a test case that we know of coming up...Apophis in 2029 will pass quite close (~ 0.1 LD), and this effect should be able to be measured. It currently sports an Sq spectrum.

MW