[meteorite-list] Comets vs. asteroids

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Tue, 13 Jan 2009 08:22:48 -0800 (PST)
Message-ID: <569641.6836.qm_at_web36907.mail.mud.yahoo.com>

Hi Bob -

A great technique - just keep repeating the same falacies again and again and again in different places, and perhaps some of them will stand.
As you put it, repeating the same phrase over and over adds nothing to the
discussion.

So let's simply go to the biggest falacy first:

> The threats that worry you we have absolutely zero ability to prevent,
and
> Knowledge of the threat doesn't mean a lot when you have no means of
> preventing it.

Coming from SDIO, you know about SSHCL, solid state heat capacity lasers, and they can be used to divert anything if it is found early enough. There's tsar bombas as well.

> We're finding the planet killers and continent killers
> at a pretty fast clip.
and
> Within a few years we will have found and ruled out all of
> the potential state-sized killers.

NASA is now finding the larger and brighter asteroids at a fairly fast clip (and by the way, getting NASA to do even that was a battle, and I've got bad scars to prove it). NASA can not adequately detect major parts of the impact hazard, specifically 75 m dead comet chunks and Long Period Comets.

> > Now that's news there - are your IR detectors
> > capable of finding 75 m objects with the luminence of a chunk of
> > charcoal at several lunar distances?
>
> Surely you must know that most catalogued asteroids are
> about as dark as charcoal. Typical reflectivities are 6-10%.

But what is the reflectivity of carbonaceous chondrite, the darkest of the dark? I'm sure some list members can give us the exact numbers.

> I chose a physical dimension because the radiance units
> (watts/cm^2-sr) would likely be of no help to you.

I'm sure some list members can break it down to photons per bucket, if you want to try it - or see the CAPS study, where that was done, that is if NASA has not destroyed all their copies of it.

>You can find them just fine in the visible; even better in the IR.

Okay, even better in the IR, so why isn't NASA using it? And LIDAR and radar work even better. Where are our space based NEO detectors?
 
> It's not the brightness that's the problem, it's the revisit rate -- a
> classic surveillance problem.

Count on no revisits. Dead comet fragments may well come along Long Period Comet paths.

> Adding one satellite helps incrementally, but it's no magic bullet.

Well, it's better than no bullet at all.

Concerning CAPS, you wrote:

> Well, now you're REALLY talking about some money. I
> doubt anyone could do it for under ten billion and in less than 10
> years. That's a pretty expensive insurance policy, in return for a very
> small incremental benefit. It's not going to pass a Congressional cost-
> benefit analysis.

It already did pass - that's why the Congress passed the George Brown Jr. ammendment to NASA's charter. As far as the benefits go, apparently the Congress did not trust NASA's numbers, and rightly so. Now since we're going to return to the Moon to keep up with China, why don't we do something useful while we're there?

E.P. Grondine
Man and Impact in the Americas









--- On Tue, 1/13/09, Matson, Robert D. <ROBERT.D.MATSON at saic.com> wrote:

> From: Matson, Robert D. <ROBERT.D.MATSON at saic.com>
> Subject: RE: Comets vs. asteroids
> To: epgrondine at yahoo.com, meteorite-list at meteoritecentral.com
> Date: Tuesday, January 13, 2009, 2:02 AM
> Hi E.P.,
>
> > What you have to weigh that high cost against is the
> fact that
> > mankind nearly went the way of the dinosaur several
> times over
> > the last six million years, and several mt DNA groups
> disappeared
> > more recently than that, and several nations
> disappeared more
> > recently than that.
>
> Well, where do you draw the line on the expense of your
> "insurance
> policy", when there is no way to cash it in if
> you're right?
> We're finding the planet killers and continent killers
> at a pretty
> fast clip. Launching a satellite or two to join in the
> search
> is a bit like confiscating shampoo bottles from airline
> passengers:
> it's "security theater". (No one is in the
> least bit safer on
> jet airlines, btw -- just more inconvenienced and
> irritated.)
> Within a few years we will have found and ruled out all of
> the
> potential state-sized killers. Beyond that, you're
> money is
> probably better spent elsewhere.
>
> > Of course, the difference between you and myself is in
> our
> > estimates of the risk. Mine is built on historical and
> geological
> > data... yours on hopes and Morrison's theoretical
> models.
>
> My threat estimate is based on my own math and
> understanding of
> solar system dynamics.
>
> > Speaking of money, how many tens of millions has NASA
> wasted looking for Nemesis?
>
> Seems to me you're simply looking for your own version
> of Nemesis.
> What makes your Moby Dick comet any more urgent or probable
> in the
> next five centuries?
>
> >> The risk, while real, is puny compared to more
> mundane threats.
>
> > While we certainly have a lot of "mundane"
> threats, risk equals
> > probability of occurrence versus loss per occurrence.
>
> Knowledge of the threat doesn't mean a lot when you
> have no means
> of preventing it. We ~barely~ have the technology to
> prevent an
> impact that is, say, a decade out. The threats that worry
> you we
> have absolutely zero ability to prevent, any more than a
> supervolcano
> eruption in Yellowstone. The smart money is spent on those
> threats
> that we CAN do something about.
>
> >> The odds of a 75-meter impactor (of any flavor)
> are indeed
> >> close to one, but only if you're willing to
> wait long enough. But you
> >> can't say the odds of being blind-sided by one
> are unity
>
> > With NASA's current and planned detectors, yes I
> can.
>
> Okay, you can say it, but that doesn't make it true.
> ;-)
>
> >>-- we have space-based sensors operating 24/7
>
> > Now that's news there - are your IR detectors
> capable of finding
> > 75 m objects with the luminence of a chunk of charcoal
> at several
> > lunar distances?
>
> Surely you must know that most catalogued asteroids are
> about as
> dark as charcoal. Typical reflectivities are 6-10%. You can
> find
> them just fine in the visible; even better in the IR.
>
> >> and dozens of highly capable ground-based
> instruments
> >> scattered around the globe, so there is at least
> some
> >> chance of spotting such an interloper before
> impact.
> >> (Don't forget the 3-meter object that Catalina
> Sky Survey
> >> spotted about a day before impact in Sudan.)
>
> > Specious rationalization of the worst sort, Bob
>
> Hardly -- it demonstrates that current ground-based
> technology
> is perfectly capable of detecting threats smaller than you
> care
> about. It's not the brightness that's the problem,
> it's the
> revisit rate -- a classic surveillance problem. Adding one
> satellite helps incrementally, but it's no magic
> bullet.
>
> > - you mention 3 meters, but you do not mention
> luminence
>
> I chose a physical dimension because the radiance units
> (watts/cm^2-sr)
> would likely be of no help to you.
>
> > Did you work the Columbia foam impact by any chance?
>
> I have no idea where you're going with such an
> unrelated topic.
> If you insist on employing sarcasm, slamming NASA, or both,
> that's
> you're business, but I don't see the relevance. I
> don't work for
> NASA.
>
> > Once again, it was a comet that killed the dinosaurs,
> not an asteroid.
> >> What's the difference?
>
> > Don't you know the difference between a comet and
> an asteroid?
>
> I do. I'm asking for relevance to the problem at hand.
> I doubt the
> city about to be wiped off the face of the planet cares
> whether the
> rock they get hit by happens to have a little ice mixed in.
>
> >> In terms of detection, there is no difference
> between an earth-crossing
> >> asteroid and a short period comet.
>
> > Oh really?
>
> Yes -- unless of course you'd like that comet to be
> active, in which case
> the comet is far easier to detect than the asteroid of
> comparable mass.
>
> >> If you're arguing that the main threat is a
> long-period comet, then
> >> fine. But a space-based sensor won't help you
> in that case.
>
> > Really?
>
> Yes, because the more sensitive ground-based instruments
> would most
> likely find it first.
>
> I asked:
>
> >> How much aperture are you talking about putting up
> in orbit?
>
> You replied:
>
> > You put it on the Moon - see the CAPS study, if NASA
> has not destroyed
> > all their copies of it.
>
> Well, now you're REALLY talking about some money. I
> doubt anyone
> could do it for under ten billion and in less than 10
> years. That's
> a pretty expensive insurance policy, in return for a very
> small
> incremental benefit. It's not going to pass a
> Congressional cost-
> benefit analysis.
>
> > One more time, it wasn't an asteroid that killed
> the dinosaurs, it was
> > a comet.
>
> So we should stop looking for asteroids? What's your
> point? Repeating
> the same phrase over and over adds nothing to the
> discussion. Context?
> Relevance?
>
> > NASA impact risks from comets and asteroids are
> published, and they're
> > defective.
>
> Some astronomers have argued the opposite -- that
> they're overly
> alarmist.
>
> > Wernher von Braun said it a long time ago: solids lack
> abort modes.
>
> True; then again, Roman Candles burn nice and slow.
> Cryogenic liquid
> tanks explode. Choose your poison. --Rob


      
Received on Tue 13 Jan 2009 11:22:48 AM PST