Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v09_4/v9_459.txt

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Subject: SPACE Digest V9 #459

SPACE Digest                                      Volume 9 : Issue 459

Today's Topics:
           Magellan Status for 05/22/89 (Forwarded)
           Magellan Status for 05/23/89 (Forwarded)
           Magellan Status for 05/24/89 (Forwarded)
           Magellan Status for 05/25/89 (Forwarded)
               News of the Week, May 24
         Re: Sun's invisible partner NEMESIS
             Oort cloud is not `mythical'
               Teach your children well
             Re: The late NEMESIS Theory
----------------------------------------------------------------------

Date: 25 May 89 05:28:17 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Magellan Status for 05/22/89 (Forwarded)

[I was on travel the past few days, hence the late postings. -PEY]

MAGELLAN STATUS
May 22, 1989


        Twice daily momentum wheel desaturations were performed with
nominal results Friday, Saturday and Sunday. Daily star
calibrations also were performed and both stars, Alpha Boots and
Gamma Crux, were detected and a full attitude update was
obtained.

        The flight team has been authorized to implement a plan to
alternate use of the high-gain and medium-gain antennas at
different attitudes to collect rocket engine module (REM)
temperature data over a period between days 150 and 190. The
information is expected to help in developing a solution to the
anticipated overheating of the REMs when the spacecraft moves
closer to the sun.

        On Saturday, the Cruise-2 sequence was uploaded to the
spacecraft. It included the trajectory correction maneuver
commands for Sunday's rocket burn which project said was "to
perfection." Cruise-2 also will provide commands for the next 12
days.




        SPACECRAFT
        Distance  From Earth (mi)                   2,642,052

        Velocity  Geocentric                         5,802 mph
                  Heliocentric                      60,057 mph

        Round Trip Light Time                           14.1 sec

------------------------------

Date: 25 May 89 05:29:03 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Magellan Status for 05/23/89 (Forwarded)


                         MAGELLAN STATUS
                          May 23, 1989


     All Magellan spacecraft systems were working well today. The
Navigation Team continued to refine its estimate of the accuracy
of the Trajectory Correction Maneuver (TCM) Sunday which appears
to be extremely precise.

     Twice daily momentum wheel desaturations and the daily star
calibration were performed as expected.

     The X-band was turned on Monday afternoon and the spacecraft
maneuvered to point the high-gain antenna to Earth for 10 hours
of activity. Just before midnight (PDT) the spacecraft was turned
to again aim the medium-gain antenna at Earth.

     The first very long baseline interferometry (VLBI)
measurements were taken Monday using 34-meter DSN stations at
Goldstone and Madrid. Also, engineering telemetry recorded
during the TCM Sunday night was successfully played back at 115.2
kilobits per second to Goldstone and relayed to JPL.






     SPACECRAFT
     Distance  From Earth (mi)                   2,780,923

     Velocity  Geocentric                         5,770 mph
               Heliocentric                      60,091 mph

     Round Trip Light Time                           14.9 sec

------------------------------

Date: 25 May 89 05:30:14 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Magellan Status for 05/24/89 (Forwarded)

MAGELLAN STATUS
May 24, 1989


        The twice daily momentum wheel desaturations and the daily
star calibration were performed as expected.

        Analysis of stored trajectory correction maneuver (TCM)
data confirmed the burn last Sunday was every bit as successful
as first indicated.






        SPACECRAFT
        Distance From Earth (mi)                   2,919,025

        Velocity  Geocentric                         5,738 mph
                  Heliocentric                      60,128 mph

        One Way Light Time                           15 sec

------------------------------

Date: 25 May 89 23:13:01 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Magellan Status for 05/25/89 (Forwarded)


                         MAGELLAN STATUS
                          May 25, 1989


     Plans are being made to place in Magellan's Cruise 4 and 5
computer command sequences information to help develop a solution
to the rocket engine module overheating problem. Starting with
Cruise-4, which will be uploaded on June 9, the spacecraft will
be turned 180 degrees around an axis through the medium-gain
antenna (MGA) to collect thermal data in a new attitude.

     Also, two new stars will be added to the star calibration
sequence in Cruise-4. The spacecraft will scan the stars of a
different spectral class to assist in adjusting the star-scanner
acceptance criteria and on-board attitude determination. Those
scans will not be updated, however.

     The twice daily momentum wheel desaturations and the daily
star calibration were performed routinely Wednesday.

     Project has determined the time of day Magellan will reach
its aim point at Venus on August 10, 1990. Without further
trajectory correction it would be 10:30 a.m. PDT. Another
trajectory correction maneuver scheduled for December, however,
will skew that time by several minutes.






     SPACECRAFT
     Distance From Earth (mi)                   3,056,363

     Velocity  Geocentric                         5,706 mph
               Heliocentric                      60,169 mph

     One Way Light Time                           15.2 sec

------------------------------

Date: 24 May 89 21:02:21 GMT
From: frooz!cfa250![e-mail]  (Jonathan McDowell)
Subject: News of the Week, May 24

Jonathan's Space Report

May 24, 1989 (no. 17)

Delta II launch due for tonight if weather allows; Kosmos-2020 is up.
The first launch of the Ariane 44L due soon.  Rather a quiet patch at
the moment, though.

Have a nice long weekend; I'm forced to take it off as our system will
be down for upgrade!

-Jonathan

------------------------------

Date: 23 May 89 14:07:04 GMT
From: nih-csl![e-mail]  (jim sullivan)
Subject: Re: Sun's invisible partner NEMESIS

In article <[e-mail]> [e-mail] (M D Ayton) writes:
>>Oh, come now!  I take it, Ed, that you will not consider Nemesis to
>>exist unless/until it is directly observed.  Does this mean you won't
>>accept the existence of electrons until someone takes a photograph of one?
>
>No, and photographs can be faked - I may not even believe my very own mark I
>eyeball!
>
>Martin.      [e-mail]

    I hope that I am reading this right because I must get out my
    flame-thrower:
    FLAME ON
    Do I take it that Ayton wants Ed to "consider" the existance of
    Nemesis without any evidence?  I know of a lot of evidence of the
    existance of electrons but very little if any evidence for the
    existance of Nemesis.  And DON'T call periodic extinctions
    evidence.  There are many theories around for the extinctions
    and Nemesis is the least favored.  I, for one, would like to
    know how a binary star system could form with an orbital period of
    20 million years with the companion getting close enough to disrupt
    the asteriod belt with the planets all seeming to have very stable
    orbits.  If you want someone to "consider" a theory without any
    evidence, call it religion, and not science.
    FLAME OFF


                    Jim Sullivan
                    [e-mail]

------------------------------

Date:     Tue, 23 May 89 14:54 EST
From: <[e-mail]>
Subject:  Oort cloud is not `mythical'

Ed Nather writes:
>Note that I did not say the theory was wrong, only unproven, and totally
>lacking in observational evidence other than the known evidence it was
>devised to explain.  It has proved to be unprovable, hence "mythical."
>I guess I would like it to be correct, since it's plausible, but my
>gullibility was shattered as a child by an unplanned close encounter
>with the tooth fairy ...

     I think it would be a good idea if you checked your dictionary
again.  Mythical does not mean unproven - rather it is something
fictional, usually with supernatural overtones.  And fictional means
that something is not true.  I agree that the location of the Oort cloud
is in dispute, and that its existence is circumstantial.  It is NOT,
however, mythical or fictional.  Rather, it is a scientific theory like
any other, one that fits the available data reasonably well and better
than any similar theory about the origin of comets.

     Your misuse of the word `mythical' insults the astronomical
community, of which you are yourself a member.

                                         -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Arnold Gill                             | If you don't complain to those who  |
Queen's University at Kingston          | implemented the problem, you have   |
gill @ qucdnast.bitnet                  | no right to complain at all !       |
                                         -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

------------------------------

Date: Tue, 23 May 89 14:45:26 CDT
From: [e-mail] (Who remembers 8USER.PAR?)
Subject: Teach your children well

>From: cfa![e-mail]  (Bill Wyatt)
>From article <[e-mail]>, by [e-mail] (Ed Nather):
>> In article <[e-mail]>, [e-mail] (Daniel Evans) writes:
>>>     A couple of years back, I had read some accounts about a tiny (non-
>>> identical) "twin" of our sun, which swings by every few million years or so.
>>> Someone referred to it as "Nemesis".

  [bunch of ASCII deleted]
>
>>>     My wife's sixth-grade students want to know...
>>
>> Teach them the difference between theory and observation, and you'll do
>> them a life-long favor.
>>
>Absolutely.
If anyone here wishes to make one positive impact on space or anything in
the realm of science,  teach your children and your neighbors basic principles
of science.  Observation, experimentation, the "scientific method".

I am never so frustrated and morose about our prospects for the future as
when I find someone misunderstanding science.  Phrases like "it's been
light-years since I saw home" (_Hard Time on Planet Earth_) or the number
of people who use the word new-cue-ler to describe a certain energy source
are just chops at our scientifc position.

Kids who learn basic scientific principles and core mathematics will never
be hurting for jobs.  I just fear that they may find themselves in too much
demand.

more paranoia in the public interest form
Dillon Pyron                         | The opinions are mine, the facts
TI/DSEG Lewisville Computer Services | probably belong to the company.
[e-mail]              |
[phone]                        | We try, we learn, sometimes we die.
                                     | We sit on our butts, learn nothing,
                                     | and we still die.

------------------------------

Date: 23 May 89 22:35:07 GMT
From: oliveb!tymix!3comvax![e-mail]  (Michael McNeil)
Subject: Re: The late NEMESIS Theory

In article <[e-mail]> [e-mail] (Ethan Tecumseh Vishniac)
writes:
>In article <[e-mail]>, [e-mail] (Bill Wyatt)
>writes:
>>Several things would have to be verified for the entire NEMESIS theory
>>to be accepted. A short list, off the top of my head:
>>
>>...list mostly deleted ..
>>5) The iridium layer(s) must be of extraterrestrial origin.
>
>The original claim was that the K-T boundary had to be.  One
>comment that I see periodically is that the same irridium anomaly
>that shows up in meteorite abundances is also present (perhaps to
>a lesser degree) in the mantle.  It follows that extensive volcanism
>*might* have a similar effect.  Any geologists following this?

I'm not a geologist, though I've been trying to follow this subject.
From what I've been able to determine, a number of geologists agree
with you.  However, there's stress on the *might*.  There's little
evidence for such a major episode of volcanism at the proper time.

>>6) There must be an Ir or other tracer layer at every extinction boundary.
>
>Although there have been some claims along these lines, I believe that
>the K-T boundary is the only well accepted instance.  Given the claimed
>periodicity and the existence of at least one more drastic (although
>earlier) extinction this seems somewhat damning.

I agree that the evidence for meteoric impacts as the cause of
other major extinction events is not particularly convincing.

>One point which I haven't seen treated much is the question of whether
>it is even necessary to explain the (debatable) periodicity using
>astronomy.  Mass extinctions appear to follow from some combination
>of climate and biology.  Dropping rocks on everything (or comets) is
>simply a crude way to ensure this.  However, climate and ecology are
>coupled, extremely complicated nonlinear systems.  One might add
>geological processes, including continental drift, to the list as
>the source of episodes of intense volcanism, disruption of ecological
>systems due to the creation of land bridges, and changes in climatic
>patterns.  It is my understanding that such systems frequently show
>oscillations on somewhat unpredictable time scales that may appear,
>at first glance, crudely periodic.

The nice thing about the iridium layer and other evidence (see below)
for an impact catastrophe as the explanation for the K-T extinction
events is that it *is* evidence.  In the past there were an endless
number of theories explaining the demise of the dinosaurs (everything
from egg-eating mammals to little green hunters in flying saucers),
but nary a shred of evidence for any of them.  This is much better.

I shan't argue in favor of periodicity -- I don't see it myself.
However, "mere" climate change, although certainly capable of
instigating large scale extinction events (and, I admit, once
such extinctions begin in tightly coupled ecologies, who knows
where they will end), still seems to me wholly insufficient in
causing the extinction of every land animal over 1 Kg in size,
and three quarters of all species, land and water, on the Earth.

>To take an extreme example, suppose mass extinctions are due entirely
>to episodes of volcanism and the K-T boundary is either a coincidence
>(comet(s) happened to hit close to such an episode) or simply reflective
>of an unusually deep upwelling of mantle material during this episode.
>Then one really needs to explain an approximate periodicity in certain
>kinds of flow patterns in the Earth's core.  I don't think this would
>strike anyone as particularly outrageous.

Extreme volcanism as a explanation of the K-T extinctions, though
perhaps not ruled out by the iridium layer (due to the possibility of
an unusually deep upwelling of mantle material, as you say), *does*
seem to be eliminated by the occurrence of shocked quartz, which has
been found at the K-T boundary all over the world.  Not only is it
thought that no volcanic eruption is violent enough to produce the
shocked quartz in the first place (I understand it has been found
in the past only at meteorite impact sites and nuclear tests), but
it is also believed that no volcanic eruption is violent enough to
have blasted the shocked quartz fragments out of the atmosphere so
they could thereupon rain down on the opposite side of the Earth.

The evidence for the reality of a single meteoric-impact extinction
catastrophe says nothing, of course, about the existence of Nemesis.

It seems to me that detractors of the impact explanation of the K-T
extinctions (I'm not accusing you of this, Ethan!) *and* proponents
of the Nemesis explanation for "periodic" extinction events are
both being reduced to arguing *possibility* rather than probability.

Yes, it *might* be possible that a massive volcanic eruption would
mimic at least some of the evidence for a K-T impact.  It *might* be
possible that a Nemesis star could withstand eons of extremely tenuous
orbit around the sun, in order to generate the not-particularly-glaring
periodicities we think we see in the geological record.  But where,
pray tell, is the evidence for a volcanic eruption?  Where is Nemesis?
These are handwaved away with talk about "But... it's *possible*!"

> I'm not afraid of dying     Ethan Vishniac, Dept of Astronomy, Univ. of Texas
> I just don't want to be     {charm,ut-sally,emx,noao}!utastro!ethan
> there when it happens.      (arpanet) [e-mail]
>    - Woody Allen            (bitnet) [e-mail]

--
Michael McNeil            [e-mail]
3Com Corporation        hplabs!oliveb!3comvax!michaelm
Mountain View, California    work telephone: [phone] x 208

    A luminous star, of the same density as the Earth, and
    whose diameter should be two hundred and fifty times
    larger than that of the Sun, would not, in consequence
    of its attraction, allow any of its rays to arrive at us;
    it is therefore possible that the largest luminous bodies
    in the universe may, through this cause, be invisible.
        P. S. Laplace, *Le Systeme du monde*, vol. II, 1795

------------------------------

End of SPACE Digest V9 #459
*******************