Asteroids - Sphericity & Solidity associated?

[Widdekind]

Most asteroids are not spherical. For example, the Martian mini-moon Phoebos "is an irregularly shaped rock just less than 28 kilometres across" whose volume is over 15% voids.

 

 

Of course, the situation is similar for smaller Deimos (Mars' other mini-moon).

 

 

Now, in addition, according to the National Geographic Channel documentary Naked Science -- Avoiding Armageddon (TV), most asteroids are "rubble piles" of loosely bound bits kept together by gravity. As an analogy, this author reminds the reader about Buzz Magnets,

 

 

Thus, most asteroids are not solid, but are, rather, pretty porous, w/ potentially vast interstitial spaces. Indeed, when such "rubble piles" pass near enough to the Earth, they suffer "seismic shakes" which turn over the top layer of regolith, exposing fresh material upon the surface*. (This would be analogous to bringing a bunched bunch of Buzz Magnets near enough to a big bar magnet, making them move into a new configuration, shifting & sliding into another shape.)

*

Comparing the images, of the bunched bunch of

Buzz Magnets

, against the photo of

Phoebos

, strongly suggests, that the "rubble pile" comprising the core of an asteroid

(=

Buzz Magnets

)

is shrouded in a thick powder of dust

(=

regolith

)

. So, when such a "rubble pile" passes near enough to Earth

(= bringing

Buzz Magnets

near a big

Bar Magnet

)

, as those chunks comprising the core slip & slide into another sort of shape, they naturally churn over the

regolith

adhering to them.

 

 

CONCLUSION (??):

 

Non-solidity seems strongly associated w/ non-sphericity. Could it be the case, that -- in the main, as a general rule -- these qualities are actually equivalent ?? To wit, that an asteroid is solid if and only if it is spherical, et vice versa ?? Indeed, when a world becomes big enough for its own self-gravity to shape itself into a sphere, such processes presumably compact & compress all "cave" interstitial spaces. (In analogy, whilst there can be caves on the surfaces of rocky planets, where gravity is weak, their are probably no caverns deep down in the Mantles or Cores of those worlds.)

---

Merged post follows:

Consecutive posts merged

ADDENDUM:

 

If asteroids are really "rubble piles", perhaps applying "Gravity Tractors" to pull the asteroid off course, or Lasers to vaporize surface rocks to push the asteroid off course, would not work. Instead, perhaps its possible that "pulling" or "pushing" on a "rubble pile" would merely move the bits about, rearranging the rocks into some new shape. Indeed, perhaps the effect would look allot like bringing such "rubble piles" past a planet -- the parts would simply shift & slide, exposing fresh regolith.

 

In-so-far as "Gravity Tractors" & Lasers rely on an assumed solidity of the asteroid, then "rubble piles" would possibly behave in an entirely different manner from such assumptions.

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Merged post follows:

Consecutive posts merged

ADDENDUM:

 

Mars' mini-moons (Phoebos & Deimos) have equatorial orbits, much like the Moon of Earth. This seemingly suggests that Phoebos & Deimos formed from a debris disk orbiting around Mars, much like the Moon of Earth.

 

Now, Earth's Moon was made from an impact, w/ a Mars-sized body (10% M_earth), about 4.5 Gya. And, Mars shows signs of a similarly-scaled-sized impact, over 4 Gya, w/ a Moon-sized body (10% M_mars) which bashed out the Borealis Basin covering the northern 40% of Mars' surface.

 

Could it be, that the Phoebos & Deimos mini-moons are really the "rubble-pile" remains, of all the bits & pieces blasted out into orbit by the "Borealis Basin impactor" ?? As with the "Theia impactor" which made the Moon of Earth, the catastrophic collision created a debris disk orbiting about the central planet. But, with Mars, much less material subsequently settled into the debris disk -- so much so, that only two non-solid, non-spherical mini-moons were made*.

 

*

According to the National Geographic Channel documentary

Traveler's Guide to the Planets -- Mars

(TV), tidal friction is pulling

Phoebos

ever closer to Mars.

Phoebos

is losing 2m of altitude per

century

, and is expected to impact Mars in

about 50 Myr

. Perhaps, then, the

Borealis Basin

impact event resulted in

many

mini-Moons... only

two

of which have survived

over 4 Ga

of tidal interactions.

 

Indeed, given that planetary formation processes so frequently involve such catastrophic encounters (inner star systems have been described as "shooting galleries"), maybe Moons & mini-moons are quite common across the Cosmos* ??

 

*

According to

Star Factories

by Ray Jayawardhana, computer simulations suggest that the

Theia

impact event created one Moon, or two Moons which soon merged (<

50 Myr

). Such suggests that, whilst many mini-moons might be quite common, major Moons might most often be single.

Edited February 20, 2010 by Widdekind
Consecutive posts merged.

[Mr Skeptic]

Non-solidity seems strongly associated w/ non-sphericity. Could it be the case, that -- in the main, as a general rule -- these qualities are actually equivalent ?? To wit, that an asteroid is solid if and only if it is spherical, et vice versa ?? Indeed, when a world becomes big enough for its own self-gravity to shape itself into a sphere, such processes presumably compact & compress all "cave" interstitial spaces. (In analogy, whilst there can be caves on the surfaces of rocky planets, where gravity is weak, their are probably no caverns deep down in the Mantles or Cores of those worlds.)

 

That is pretty much it. If something is large enough to pull itself into a sphere, most of the voids in it will get filled as the pressure becomes significant.

 

If asteroids are really "rubble piles", perhaps applying "Gravity Tractors" to pull the asteroid off course, or Lasers to vaporize surface rocks to push the asteroid off course, would not work. Instead, perhaps its possible that "pulling" or "pushing" on a "rubble pile" would merely move the bits about, rearranging the rocks into some new shape. Indeed, perhaps the effect would look allot like bringing such "rubble piles" past a planet -- the parts would simply shift & slide, exposing fresh regolith.

 

In-so-far as "Gravity Tractors" & Lasers rely on an assumed solidity of the asteroid, then "rubble piles" would possibly behave in an entirely different manner from such assumptions.

 

Gravity tractors will have no problem with rubble piles; gravity acts on all the rubble. Lasers probably will have no trouble either: rubble piles do have gravity you know. So long as the laser pushes it slowly, and honestly we don't have lasers powerful enough to push something fast, then it will still hold together. Use of kinetic impactors or bombs, on the other hand, could end up with lots of slightly deflected rubble all over the place.

 

Remember also, that the slow methods are intended to deflect only by tiny amounts well ahead of time, a fraction of a degree off its original path will do.

[Widdekind]

Thanks for the reply.

 

The image of the "Buzz Magnets" has become broken, but here's the same (if smaller) picture:

 

 

Also, Mars' inner moon (Phoebos) is more massive than the outer moon (Deimos)*. Thus, the "mass profile" of Mars' moon system decreases w/ increasing radius. This is conspicuously completely consistent w/ claims, and so seemingly suggests, that "Phoebos & Deimos formed from a debris disk orbiting around Mars, much like the Moon of Earth" (as per PP).

*

http://en.wikipedia.org/wiki/Deimos_(moon

)