[meteorite-list] NEA ASTEROIDS, ALBEDOS, AND ORIGINS

[MarkF]

Hi Sterling

Great questions that the researchers really need to hear before they publish 
to the world about what killed dinosaurs!
I do believe more research on the effects of impactors needs to be done so 
that definitive answers can be found for these and other questions and Tesla 
can be let off the hook for Tunguska.

Mark Ferguson
----- Original Message ----- 
From: "Sterling K. Webb" <kelly at bhil.com>
To: "drtanuki" <drtanuki at yahoo.com>; "Meteorite List" 
<meteorite-list at meteoritecentral.com>
Sent: Sunday, June 26, 2005 8:22 PM
Subject: [meteorite-list] NEA ASTEROIDS, ALBEDOS, AND ORIGINS


> drtanuki wrote:
>
>> Sterling,
>>    A question I have pondered. What if an incoming body has no
>> reflectance whatsoever, therefore invisible?  Best, Dirk Ross...Tokyo
>
>    A very good question!  And a worrying one.  The answer to "what if
> there is an "invisible" potential impactor" is:  BAD LUCK!
>
>    A body that makes repeated close passes to the Sun in its orbit will
> suffer very high surface temperatures. If the body is icy or a comet, it
> will "come alive" with the evaporation of its volatiles and brighten,
> but a carbonaceous body or even a rocky one will darken, more with each
> passage.  The "potato" asteroid will become a "baked potato"!  And
> eventually, a "charred" potato.
>
>    Bamberga, in the darkest, low-albedo C-class of carbonaceous
> chondrites, has an albedo of less than 0.05.  That's the record low, I
> think, but Bamberga is in the Belt and doesn't venture near the Sun.
> Its darkness is from its primordial composition.  A similar object that
> did approach the Sun, would almost certainly darken down to 0.02 or
> 0.01, which is the same as saying that it would be functionally
> "invisible."  Until the very last minute, that is.
>
>    My first thought was that since a Sun close approacher's orbit would
> be anchored by the greatest mass in the solar system, it would be very
> imperturbable, but no, it seems Jupiter does a fine job of causing
> certain kinds of perturbations, precessing tightly bound solar orbits.
> One less comfort.  So, such a body does constitute a hazard that we
> can't calculate the likelihood of, and that's worrying.
>
>    Many think (or thought) that some NEA's may be "dead" comets or
> baked once volatile bodies, hence structurally weak and subject to
> further degradation over time which might mitigate their hazard slightly
> -- it would be better if they crumbled to rubble rather than smacking
> our little planet, or anybody's little planet.
>
>    But, then I ran across a study carried out by ESA's Infrared Space
> Observatory (ISO).  The surfaces of most NEA's examined are rocky and
> almost entirely free of small rubble, regolith and dust.
>
>    Why is that important?  Because it strongly implies that NEA's
> originate, not in being perturbed into NEA-style orbits, but acquire
> these orbits because of recent collisions and mutual impacts that
> fragment solid bodies and knock every bit of the loose stuff clean off.
>
>    Thus, the NEA's seem to be former impactors and impactees.  They got
> to where they are because of bad luck.  Given the long-term instability
> of NEA orbits, their run of bad luck is not over.  Only now, their bad
> luck could also be our bad luck...
>
>    I should stress here that the current "professional" belief is very
> strong that NEA's get into Near Earth orbits almost entirely through a
> long series of perturbations by weak orbital resonances and the action
> of the Yarkovsky effect of sunlight on their motion, and NOT by
> collisional mechanisms, which are pretty much dismissed as "too rare."
>
>    These are mechanisms that produce a slow and non-dramatic trickle of
> outer system bodies to be delivered gently to the inner solar system and
> become NEA's.  But that opinion is flatly contradicted by the ISO study
> results which show NEA's to be unlike Main Belt asteroids transported
> gently with all their regolith and surface junk intact.  NEA's have
> undergone some alteration process, almost certain to have been
> collisional.
>
>    Another explanation could be that today's NEA's are the depleted
> remnant of much larger NEA population in the past, one that was produced
> by a really big "recent" collisional event or events.  I put the quotes
> around "recent" because I mean astronomically recent, like half a
> billion years or less!  That's ten percent of the age of the solar
> system or less.  If you're thirty, don't you think of the last three
> years of your life as recent?
>
>    That notion, for example, would explain a paradox about Chicxulub
> (the dino killer, or not, set free by a California jury, as you see
> fit).  Namely, that it's TOO BIG for its "recent" date.  That was one of
> the strong objections when the idea of explaining the iridium by impact
> was first proposed.  Impacts that large are far rarer than one per
> 100,000,000 years, more in the one per 1,000,000,000 year class.
>
>    The upper size estimates for Chicxulub would mean that it might have
> been the biggest impactor to strike the Earth in several billions of
> years, an odd piece of bad luck (if you're a dinosaur). And, recent
> research in Cuba on "overturned" sediments suggest it may have been an
> even bigger impactor than present estimates. Additionally, the Chicxulub
> "crater," instead of being a two or three ring basin as originally
> thought, well, it now develops that there are five rings and probable
> traces of a sixth.  BIG.
>
>    It's hard to explain how a body the size of Chicxulub could "evolve"
> by no other force than weak resonances and the Yarkovsky effect acting
> over 4,500,000,000 years until finally one "recent" day it is suddenly
> plopped into an Earth intersecting orbit and -- SMACK!
>
>    This is not geology, folks, where the gentle rain wears mighty
> mountains away a grain of sand at a time.  We're talking about orbital
> shift, big, sudden, dramatic change (with an option on violence).  This
> is like the mountains suddenly jumping up and crashing back down on a
> new continent far away.  Long runs of small forces (rain) doesn't do
> things like that.
>
>    Big bodies, fat chunky asteroids, small moons -- they either last
> forever or run into trouble in a big hurry.  The Centaur orbits, between
> Saturn and Uranus, where the giant 250-mile diameter 2060 Chiron (aka 95
> P/Chiron) sleeps, have a dynamic lifetime of about 100,000 years or
> less!  Chiron's orbit is a rest stop; it's going to pull out onto the
> Interstate again, and soon. Wanna be on the road when it does?  Me
> neither.
>
>    As you can see from the naming confusion, we don't know if 2060
> Chiron is an asteroid of a comet.  Of course, with a 250 mile diameter,
> does it matter? Chicxulub was an asteroid and NOT a comet, by the way.
> See:
> <http://www.news.uiuc.edu/scitips/02/1025craters.html>
>
>    I never did understand why whenever there's a contradiction in which
> a truth may hide, someone always drags in comets and icy bodies, about
> which we know so little, as if you could explain one mystery by
> assigning it to another mystery.
>
>    Where did Chicxulub come from?  Musta been a comet.
>
>    Why is there no crater at Tunguska?  Musta been a comet.
>
>    Why does the Earth have so much water?  Musta been comets. (They
> couldn't find Venus?)
>
>    Why only four tektite producing impacts in 35,000,000 years when
> there were hundreds of other impacts in that time that didn't produce
> any tektites?  Musta been a comet.
>
>    And so on...
>
>    Not knocking comets, you understand, just the way they get stuck
> with the blame for everything...
>
>
> Sterling K. Webb
> ------------------------------------------------
>
>
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list