NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/sci/astro/14363

Text File | 1993-01-24 | 9.0 KB | 190 lines

Newsgroups: sci.astro
Path: sparky!uunet!well!metares
From: [e-mail] (Tom Van Flandern)
Subject: Re: Asteroidal Satellites (was Re: Toutatis Captured by Radar Images)
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Date: Sun, 24 Jan 1993 06:12:11 GMT
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[e-mail] (Leonard Abbey, F.R.A.S.) writes:

> Tom, what are the stats on binary asteroids?  10%?  5%?

     The observations suggest that > 70% of all numbered asteroids are
binary (either contact binaries, or with current orbiting satellites).  But
the only observations that have sampled many asteroids yet are occultations
and radar ranging.  Radar often shows complex or bifurcated images, leaving
the interpretation ambiguous.  Results from occultations of stars are clear
and unambiguous, in my judgment as a long-time analyst of occultation data.
But astronomers reluctant to accept the implications of such statistics
have disputed the reliability of the observations themselves.  They propose
that the observers are seeing secondary occultations by birds, planes, and
supermen, but not asteroid satellites.  About three dozen secondary
occultations have been reported to date, but only two cases have been
confirmed by independent observers.

     I think history will judge this as another case of denying good
observations that tend to disprove a popular theory.

> Can we determine if any of them are in "low" orbit.....pre-contact cases?

     No, because observations generally catch them at only one instant, so
we cannot determine their orbits.  And satellites inside the synchronous
orbit decay so rapidly (about 10,000 years) that we are quite unlikely to
catch that happening.


and [e-mail] (Bill Higgins-- Beam Jockey) writes:

> How well could Ostro's group detect or rule out satellites of Toutatis
> using their radars?

     I seem to recall that they will eventually reach a bit better
than 100 m resolution after their data is fully processed.
Satellites that small or smaller would be unlikely to be spotted.
Even somewhat larger objects may be overlooked as noise (which
there is a lot of) unless the data analysts are carefully guarding
against missing such a signal.

     In short, their data would probably detect relatively large
satellites near the synchronous orbit, but not smaller ones out to
the limits of the 200 km sphere of influence.

> Is this a good way to search for evidence of asteroidal satellites?

     The majority of the dozen or so main belt asteroids they have ranged
are showing complex or bifurcated images.  Obviously the Space Telescope
will be able to search more asteroids faster than either radar or
occultations.


Earlier, I wrote:

>> The rms velocity between any two asteroids is about 5 km/s -- somewhat
>> more near the Earth's orbit.  Collisions between such objects would be
>> catastrophically destructive.  So the joined fragments must have been
>> previously in orbit as satellites of the asteroid, brought down
>> gradually by tidal forces until a gentle contact occurred.

and [e-mail] (Richard A. Schumacher) replied:

> Mmmm, not necessarily.  A small body striking a larger one might easily
> disrupt the larger without dispersing the pieces.

     If the small body is small enough, it sticks; if large enough, the
collision is catastrophic.  In between, one gets fragmentation.  Fragments
either fly off faster than escape velocity and never return, or stay below
escape velocity and smack into the surface again one revolution later.  One
can't get stable, orbiting satellites that way, and even a contact binary
could only arise as a fluke, not as a common result.  It would require
neatly splitting the larger asteroid into two pieces that move apart far
enough to rotate so they wouldn't just reassemble, and then fall back and
touch gently.  Not a frequent occurrence.

> I'll predict that higher resolution images will show most of [contact
> binaries] to consist of "rubble piles", that is, many pieces of varied
> sizes, not just two big ones.  ...  What does your theory predict?

     I guess you haven't seen the images of Toutatis yet.  It looks like
two irregular, roundish, Phobos-like objects: a 2.5-km one resting on the
surface of a 4-km one.  That's what I would expect from tidal decay of
orbiting satellites.  Since I've seen the pictures, I'll have to refer to
my previously published papers for my predictions.  My most complete
exposition is in "Asteroids," U. of Arizona Press (1979), T. Gehrels, ed.,
paper titled "Satellites of asteroids" with Tedesco & Binzel, pp. 443-465.
It describes the occultation results to that time, lightcurve evidence,
dynamical considerations such as gravitational, collisional, and tidal
stability, and implications for origins and models.  More recently see
"Minor satellites and the Gaspra encounter," pp. 609-612 of "Asteroids,
Comets, Meteors 1991," Harris & Bowell, eds., Lunar & Planetary Inst.
(1992).

>> The prediction that asteroid satellites are numerous and commonplace
>> originates from the exploded planet hypothesis.  There is presently no
>> other known way to produce abundant asteroids with current or former
>> satellites.

> Indeed.  Further bold prediction: high resolution images will show nearly
> no co-orbiting asteroids or asteroids with satellites.

     I sure like my odds pitting my prediction against yours, since I've
analyzed the occultation reports, and feel I already know the outcome.  But
for those who challenge the reliability of the existing data, Galileo and
HST will soon tell the rest of the story.

> By the way: is the exploded planet idea a consequence of your Meta
> Theory?

     That's neat: the history of the universe and the solar system wrapped
up into one comprehensive model.  :-)  Sorry, no connection, other than my
personal interest in origins of everything.


and [e-mail] (Leigh Palmer) writes:

> the 5 km/s rms two-particle velocity is indeed a nice number; I'd never
> seen it before. I'd like to know a little of the detail which went into
> the calculation (a citation, perhaps, or will it be in the book?).

     The number refers to the mean speed at which random main-belt
asteroids pass one another at their points of closest approach.  It
compares to the 25 km/s rms speed among stars in the solar neighborhood of
our galaxy.  The number is not mine, and not new.  I expect it must appear
half-a-dozen times in the two "Asteroids" books, but I don't have a
specific page reference handy.

     I didn't understand your remark about closing velocities.  But if it
is relevant to your question, asteroids have too little gravity to
significantly alter the approach velocity of a colliding object.


and [e-mail] (Ben Zellner) writes:

> Toutatis was indeed a surprise.  But the "observed abundance" is still
> very small.  Extensive groundbased surveys looking for satellite objects
> separated by an arcsecond or more have been uniformly negative.  We have
> an approved Space Telescope program to look down to the HST resolution
> for a dozen or more candidate objects.  A year from now, I'll let you
> know what we saw.

     Charon is often separated from Pluto by one arc second, and the
magnitude difference is only about 1.5; yet its a problem to see under most
conditions.

     We all eagerly await the Space Telescope program results.  Be prepared
for a major discovery.  :-)

     My present interest is not so much to second-guess what future
observations will show as to lock predictions in place -- surely an
important part of the scientific process.  The solar nebula origin
hypothesis for asteroids clearly indicates that satellites must be rare,
since capture is virtually impossible and stable orbits rarely originate
from collisions.  Moreover, collisions in 4.5 billion years should have
disrupted any original satellites that did exist.

     By contrast, the exploded planet origin hypothesis predicts that all
asteroids had satellites a few million years ago.  All those inside the
synchronous orbit would tidally decay and would now be contact "binaries."
The majority of asteroids smaller than 40 km diameter have been involved in
collisions, which strips their satellites (creating families and "jet
streams").  But the overwhelming majority of the larger asteroids
(excluding the first four) will still have numerous satellites at or
outside the synchronous orbit.  Their sizes will range from the nucleus
size down to dust size.

     So the respective predictions are *rare* or *abundant* satellites.  I
hate to see wild ad hoc theorizing to explain observational results in
conflict with a favored theory.  The discovery of abundant satellites
*should* falsify the standard paradigm for asteroid origin from a primeval
solar nebula.  The discovery that satellites are rare falsifies the
exploded planet hypothesis.  -|Tom|-

--
Tom Van Flandern / Washington, DC / [e-mail]
Meta Research was founded to foster research into ideas not otherwise
supported because they conflict with mainstream theories in Astronomy.