> How so? If planets, moons and asteroids are formed by clumps
> of irregular debris accreting and clumping together by the
> force of gravity, then of course there’ll be hollows in between
> the clumps. I had Phobos, Mars’ larger moon, in mind when I
> wrote that, as Phobos has such voids.
That's not really how the theory works. In the example of the the Giant Impact Hypotheses you have two bodies colliding with such force the ejected material is turned to magma/plasma which eventually cools to form another body. Planets are not made of pieces that are stuck together by gravity, they are pieces which struck the host, either by gravity or trajectory, and were essentially "melted" by obliteration and assimilation into the greater whole. This is a very violent and chaotic process. Its pretty easy to understand the when you look at the:
What you have is a molten blob and when it eventually begins to cool the heavy metals, namely iron, sink to the center changing its angular momentum causing it to rotate on its axis. The iron core, surrounded by an outer core of liquid iron, creates the dynamo that generates a bodies magnetic field. Venus, Mars, and the Moon, for example have very weak magnetic fields suggesting at some point either their dynamo shut down or never got started, essentially meaning the liquid core solidified or was non-existent. When you think about planetary formation by way of an accretion disk, you have super-heated dust particles that attract each other by way of static electricity creating bigger and bigger particles until you have planetesimals and at the point when the objects have enough mass gravity begins to kick in attaching even more material. Eventually the attaching becomes smashing, a very hot and violent process. Supposedly this is what leads to the formation of planets, but there are some challenges to this.
Analysis of Mars Express radio science data gave new
> information about the mass of Phobos based on the gravitational
> attraction it exerts on the spacecraft. The team concluded that
> Phobos is likely to contain large voids, which makes it less
> likely to be a captured asteroid.
> It is possible that Phobos formed in situ at Mars, from ejecta
> from impacts on the Martian surface, or from the remnants of a
> previous moon which had formed from the Martian accretion disc
> and subsequently collided with a body from the asteroid belt.
> Data from the Mars Express OMEGA spectrometer suggests Phobos
> has a primitive composition, so primitive materials must have
> been available for accretion during its formation. The circular
> orbit suggests that Phobos formed in situ whilst analysis of
> the Planetary Fourier Spectrometer data from Mars Express also
> points towards in situ formation but does not rule out the
> possibility that Phobos is a captured achondrite-like
It is interesting you would bring this up because some consider Phobos an artificial satellite as well because of its large hollow spaces. [tommytoy.typepad.com]
Watch this video:[www.youtube.com]
This website is very interesting:[www.marsanomalyresearch.com]
As Carl Sagan said:
"A natural satellite cannot be a hollow object."
> There are many interesting
> > holes on the Lunar surface like this:
> > which are speculated to be lava domes (lava tube skylights).
> > Regardless, finding these holes suggests "...it may have
> > confirmed a theory that scientists had held about the Moon
> > since the 1960s - its surface may hide a vast network of
> Yes, collapsed lava tubes can easily account for holes near the
> surface, which you’ve shown photos of. If this is what you had
> in mind when you responded, then I misread what you said, and
> thought you were referring to deep voids, the kind I mentioned
These lava tubes are problematic, among other reasons, because there is no associated ejecta around their opening which is why they aren't entirely sure this is what they are. Might be, might not. Regardless, they have suspected a vast network of tunnels to explain why the Moon appears have large hollow spaces, but if these are lava tubes, especially considering there should be so many, there will be large voids as is common when such tubes converge, maybe surprisingly large, as it is likely the tubes themselves cannot adequately explain the phenomenon observed.
Post Edited (30-Jan-13 18:20)