Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_5/V16NO504.TXT

Internet Message Format | 1993-07-13 | 29KB

Date: Sun,  2 May 93 05:00:25
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #504
To: Space Digest Readers
Precedence: bulk


Space Digest                Sun,  2 May 93       Volume 16 : Issue 504

Today's Topics:
           ASTRONAUTS---What does weightlessness feel like?
                   Commercials on the Moon (2 msgs)
                              DC-X news
            Gamma Ray Bursters. positional stuff. (3 msgs)
             Gamma Ray Bursters. WHere are they. (4 msgs)
           Gamma Ray Bursters How energetic could they be?
                        HST Servicing Mission
             HST Servicing Mission Scheduled for 11 Days
                            HyperKnowledge
            Lindbergh and the moon (was:Why not give $1G)
                       Long term Human Missions
                    Vandalizing the sky. (2 msgs)
                      What planets are habitable

    Welcome to the Space Digest!!  Please send your messages to
    "[e-mail]", and (un)subscription requests of the form
    "Subscribe Space <your name>" to one of these addresses: listserv@uga
    (BITNET), rice::boyle (SPAN/NSInet), utadnx::utspan::rice::boyle
    (THENET), or [e-mail] (Internet).
----------------------------------------------------------------------

Date: 29 Apr 93 16:15:01 GMT
From: Jerry Liebelson <[e-mail]>
Subject: ASTRONAUTS---What does weightlessness feel like?
Newsgroups: sci.space,sci.astro

 I understand the when one is in orbit, the inward force of gravity at
one's center of mass is exactly balanced by the outward centrifugal
force from the orbiting motion, resulting in weightlessness.

 I want to know what weightlessness actually FEELS like. For example, is
there a constant sensation of falling? And what is the motion sickness
that some astronauts occasionally experience?

 Please reply only if you are either a former or current astronaut, or
someone who has had this discussion first-hand with an astronaut.
Thanks!

--
Jerry Liebelson
[e-mail]
[e-mail]

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

Date: Thu, 29 Apr 93 12:39:11 GMT
From: Hans Erik Martino Hansen <[e-mail]>
Subject: Commercials on the Moon
Newsgroups: sci.space

I have often thought about, if its possible to have a powerfull laser
on earth, to light at the Moon, and show lasergraphics at the surface
so clearly that you can see it with your eyes when there is a new
moon.

How about a Coca Cola logo at the moon, easy way to target billions of
people.

Do you know if its possible?


--
Erik M. Hansen    |  Email [e-mail]
Fuglsangsalle 69  |  Aarhus University
DK-8210  rhus V  |
Denmark, Europe   |

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

Date: Thu, 29 Apr 1993 14:25:26 GMT
From: Tom O'Reilly <[e-mail]>
Subject: Commercials on the Moon
Newsgroups: sci.space

[e-mail] (Hans Erik Martino Hansen) writes

> How about a Coca Cola logo at the moon, easy way to target billions of
> people.

Arthur C. Clarke was way ahead of you on this one... he wrote a short story
(title?) in the 1950s describing exactly your proposal!

Tom O'Reilly
Department of Geology
Arizona State University

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

Date: 29 Apr 1993 15:08:19 GMT
From: Andy Cohen <[e-mail]>
Subject: DC-X news
Newsgroups: sci.space

Static test firings are now scheduled for this Saturday.....after many
schedule changes.....

It may be difficult to get test status during the next two weeks....the
number of contacts are drying up as they all go to New Mexico......GO DELTA
CLIPPER!!

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

Date: 29 Apr 93 01:08:47 -0600
From: [e-mail]
Subject: Gamma Ray Bursters. positional stuff.
Newsgroups: sci.space,sci.astro

In article <[e-mail]>, [e-mail] (Kevin W. Plaxco) writes:
> In article <[e-mail]> [e-mail] (David Ward) writes:
>
>>Given that fact, and the spacecraft attitude knowledge
>>of approx. 2 arcmin, we might be able to figure out how well BATSE can
>>determine the location (rotational) of a Gamma Ray burster from knowledge
>>of the all-sky map's accuracy.  PR material for the other three instruments
>>give accuracies on the order of "fractions of a degree", if that's
>>any help.
>
> But I believe that there is a fundamental difference here.  The other x
> three instruments are focusing instruments, that, more or less, form
> an image, so positional errors are limited by craft attitude and the
> resolving power of the optics.  BATSE is an altogether different
> beast, effectively just 8 coincidence counters, one on each corner of
> the craft.  Positional information is triangulated from the
> differential signal arrival times at each of the detectors.
> Positional error would be predominantly determined by timing errors
> and errors in craft attitude. Since none of the 8 BASTE detectors have
> any independant angular resolution whatsoever, they can not be used to
> determine parallax.  Indeed, parallax would just add a very small
> component to the positional error.
>
> Demonstrating that these puppies are beyond the oort cloud would
> require resolution on the order of arcseconds, since the oort
> cloud is postulated to extend to about 0.5 parsec (all together
> now: "Parallax ARc SECond", a parsec is the distance of an object
> that demonstrates one arc second of parallax with a 2 AU base line).
> If the 3 degree accuracy reported above is true, we're going to
> have to add a BASTE to the pluto fast flyby to get enough baseline.
>
> The beauty of BASTE is that it both gives positional information and
> watches the entire sky simultaneously, a realy handy combination
> when you have no idea where the next burst is coming from.
>
> -Kevin
        Batse alone isn't always used to determine position.  WHen a
particularly bright burst occurs, There are a couple of other detectors that
catch it going off.  Pioneer 10 or 11 is the one I'm getting at here.  This
puppy is far enough away, that if a bright burst happens nearby, the huge
annulus created by it will hopefully intersect the line or general circle given
by BATSE, and we can get a moderately accurate position. Say oh, 2 or 3
degrees. That is the closest anyone has ever gotten with it.
        Actually, my advisor, another classmate of mine, and me were talking
the other day about putting just one detector on one of the Pluto satellites.
THen we realized that the satellite alone is only carrying something like 200
pounds of eq.  Well, a BATSE detector needs lead shielding to protect it, and 1
alone weighs about 200 pounds itself.

        We decided against it.
                                                        -jeremy

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

Date: Thu, 29 Apr 1993 11:04:12 GMT
From: Paul Dietz <[e-mail]>
Subject: Gamma Ray Bursters. positional stuff.
Newsgroups: sci.space,sci.astro

In article <[e-mail]> [e-mail] writes:

> getting at here.  This puppy is far enough away, that if a bright
> burst happens nearby, the huge annulus created by it will hopefully
> intersect the line or general circle given by BATSE, and we can get a
> moderately accurate position. Say oh, 2 or 3 degrees. That is the
> closest anyone has ever gotten with it.


You can do a whole hell of a lot better than 2 or 3 degrees with
the differential timing measurements from the interplanetary network.
Ignore the directional information from BATSE; just look at the time
of arrival.  With three detectors properly arranged, one can often
get positions down to ~arc minutes.

BTW, about Oort cloud sources: shouldn't this be testable in the
fairly near future?  Some of the GRBs have very short rise times (< 1
ms).  We could detect the curvature of the burst wavefront out to a
distance of on the order of b^2/(t c) where b is the detector spacing
and t the time resolution.  For t = 1 ms and b = 2 AU, this is on the
order of 16 light years.  I understand statistics will reduce this
number considerably, as would geometry if the burst is coming from the
wrong direction.

    Paul

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

Date: Thu, 29 Apr 1993 15:29:14 GMT
From: Henry Spencer <[e-mail]>
Subject: Gamma Ray Bursters. positional stuff.
Newsgroups: sci.space,sci.astro

In article <[e-mail]> [e-mail] writes:
>        Actually, my advisor, another classmate of mine, and me were talking
>the other day about putting just one detector on one of the Pluto satellites.
>THen we realized that the satellite alone is only carrying something like 200
>pounds of eq.  Well, a BATSE detector needs lead shielding to protect it,
>and 1 alone weighs about 200 pounds itself.

Actually, the situation is even worse than that.  The *total mass* of the
Pluto Fast Flyby spacecraft is only 250ish pounds, and most of that is
support equipment like power and communications.  The mass available for
instruments is maybe 10% of that.  I don't think a BATSE will fit...

Actually, would you need the shielding?  My understanding is that it's
mostly there to give the detectors some directionality.  No point in
doing that if you've only got one.  I'm sure the burst detectors that
have flown on other deep-space missions haven't weighed that much.
(Mind you, they're probably still too heavy -- the PFF people would put
more Pluto-specific instruments on first, if they had any mass to spare.)
--
SVR4 resembles a high-speed collision   | Henry Spencer @ U of Toronto Zoology
between SVR3 and SunOS.    - Dick Dunn  |  [e-mail]  utzoo!henry

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

Date: 29 Apr 93 06:29:35 GMT
From: Ethan Bradford <[e-mail]>
Subject: Gamma Ray Bursters. WHere are they.
Newsgroups: sci.astro,sci.space

In article <[e-mail]> [e-mail] (Steinn Sigurdsson) writes:

   This does not propose a _mechanism_ for GRBs in the Oort (and, no,
   anti-matter annihilation does not fit the spectra at least as far
   as I understand annihilation spectra...). Big difference.
   That's ignoring the question of how you fit a distribution
   to the Oort distribution when the Oort distribution is not well
   known - in particular comet aphelia (which are not well known)
   are not a good measure of the Oort cloud distribution...

Merging neutron stars is at least a mechanism with about the right
energy, except it doesn't explain why there is no apparent correlation
with galaxies or galaxy structure, there is no mechanism for getting
all the energy out in gamma rays (with any significant amount of
baryons around there will be a lot of pair production, which makes a
plasma, which thermalizes the energy), it has trouble generating
enough energy to explain the most powerful bursts (10^52-53 ergs), it
happens too fast compared to the burst duration, and it is hard to
make tight-binaries of neutron stars.

Another cosmological mechinism is the catalytic conversion of a
neutron star to a strange star or the merger of two strange stars, but
that uses pretty far-out physics.

My point is that we don't have a good mechanism at any distance, so
GRB's are likely to be happening by an unknown mechanism, so we can't
rule out the Oort cloud.  What would be the spectrum of an event which
converts a comet to strange matter?  The spectra for primordial black
holes eating comets and antimatter comets colliding with matter comets
aren't quite right, but perhaps there is an unusual mechanism which
modifies the spectrum.  The energy matches very well for both of these
mechanisms.  According to Trevor Weeks, if the "Tunguska Meteorite"
was a mini-black hole collision with the earth, then there are likely
to be enough mini-black holes around that the rate for BH-comet
collisions matches the GRB rate well.

The fact that we don't know the distribution of comets in the Oort
cloud isn't a reason to rule them out; it makes it harder to rule them
out.  The point of the cited paper was that if we assume they got the
right distribution for the Oort cloud, it is hard but not impossible
to match that up with the distribution of GRB's.  If they got the
wrong distribution for the Oort cloud, they can't constrain any Oort-
cloud GRB's at all.

Executive summary: we don't know enough to rule out out the Oort
cloud.

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

Date: 29 Apr 93 07:16:20 GMT
From: Ethan Bradford <[e-mail]>
Subject: Gamma Ray Bursters. WHere are they.
Newsgroups: sci.astro,sci.space

[e-mail] (Walker Andrew John) writes:
       Also,if they did come from the Oort cloud we would expect to
   see the same from other stars Oort Clouds.

That's a very good point.  Perhaps none of the nearby stars have Oort
clouds?  Alpha-centauri is a multiple-star system; you wouldn't expect
an Oort cloud in it.  What's the nearest single-star that is likely to
have a planetary system?

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

Date: 29 Apr 1993 16:19:15 GMT
From: "David M. Palmer" <[e-mail]>
Subject: Gamma Ray Bursters. WHere are they.
Newsgroups: sci.space

[e-mail] (Pat) writes:
>...
>4)  we know it's not real close,  like  slightly extra solar,  because
>we have no parallax measurements on the bursts.

We can only say that they are beyond about 25 AU, due to the low
accuracy of position determination by single detectors.

>what i am wondering,  is this in people's opinion,  A NEW Physics problem.
>Einstein got well known for solvingthe photoelectric effect.
>Copernicus,  started looking at  irregularities in planetary motion.
>Is this a big enough problem, to create a new area of physics?
>just a little speculative thinking folks.

It may be a NEW Physics problem (i.e. a problem involving new
physics).  However, the data is not good enough to rule out the >100
models which use old physics.  New physics is a big step, and is only
tolerated when there is no alternative.  For example , the Dark Matter
Problem (there's more to the universe than meets the eye) is a question
of comparable mystery to GRBs, but we have much better data regarding
it.  Theoreticians postulate new particles all the time to explain it,
but no one will actually believe that these particles are real until an
experimentalist (or several) detects them in the lab.

--
        David M. Palmer        [e-mail]
                    [e-mail]

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

Date: 29 Apr 1993 11:42 CDT
From: [e-mail]
Subject: Gamma Ray Bursters.  WHere  are they.
Newsgroups: sci.space

In article <1rlrpv$[e-mail]>, [e-mail] (Pat) writes...
>

>Is this a big enough problem, to create a new area of physics?
>just a little speculative thinking folks.
>
>pat


Well pat for once I agree with you and I like your first idea that you had.
IT probably is the gamma ray signature of the warp transitions of interstellar
spacecraft! :)

Well it makes as much sense as some things. I was at the first Gamma Ray
Burst conference here at UAH and had great fun watching the discomfiture
of many of the Gamma Ray scientists. Much scruitiny was given to the
data reductions. I remember one person in particular who passionately declared
that the data was completely wrong as there were no explanation for the
phenomena of the smooth sky distribution. (heck it even shoots down the
warp transition theory :(. The next conference is soon and I will endeavour
to keep in touch with this fun subject.

Dennis

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

Date: 29 Apr 1993 16:03:28 GMT
From: "David M. Palmer" <[e-mail]>
Subject: Gamma Ray Bursters How energetic could they be?
Newsgroups: sci.space,sci.astro

[e-mail] (Pat) writes:

>In article <[e-mail]> [e-mail] writes:
>|energetic for close by.  for the coronal model, we found around 10^43 erg/sec.
>|And lastly, for the cosmological model an L=10^53. That's what you'd call
>|moderately energetic, I'd say.  Any suggestions about what could put out that
>|much energy in one second?
>>                                                -jeremy

>big Capacitor :-)   Real Big  capacitor.

It's been suggested.  (Specifically, lightning strikes between clouds
in the interstellar medium.)

--
        David M. Palmer        [e-mail]
                    [e-mail]

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

Date: Thu, 29 Apr 1993 15:01:57 GMT
From: [e-mail]
Subject: HST Servicing Mission
Newsgroups: sci.space,sci.space.shuttle,sci.astro

In article <[e-mail]>, [e-mail] writes:
>
> I have never heard of any serious consideration that HST might be brought
> down for refurbishment.  You would have the horrendous cost of transporting,

Back in January and February there were several articles (Wash Post, Time...)
saying that NASA was "considering" the option just as it is now "considering"
a followup mission 6-12 months after the servicing mission.  However, the
down time was estimated to be a year+ (servicing, checkout, sceheduling
and training another shuttle, orbit verification...) and to be quite
expensive.  I think it may have been more a mental exercise than a
real plan.  Don't know.


----------------------------------------------------------------------------
Robert Dempsey                                 [phone]
STScI/PODPS

"He which hath no stomach for this fight, Let him depart; his passport
shall be made, and crowns for convoy put into his purse: We would not die
in this man's company that fears his fellowship to die with us." -Shakespeare
------------------------------------------------------------------------------

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

Date: Wed, 28 Apr 1993 19:19:04 GMT
From: Greg Moore <[e-mail]>
Subject: HST Servicing Mission Scheduled for 11 Days
Newsgroups: sci.space,sci.space.shuttle,sci.astro

In article <1rd1g0$[e-mail]> [e-mail] (Pat) writes:
>
>My guess is  why  bother with  usingthe shuttle to reboost?
>
>why not  grapple,  do all said fixes,   bolt a small  liquid  fueled
>thruster module  to  HST,   then let it make the re-boost.  it has to be
>cheaper on mass then usingthe shuttle as a tug.   that way, now that
>they are going to need at least 5  spacewalks,  then they can carry
>an EDO pallet,  and  sit on station and even  maybe do the  solar array
>tilt  motor  fix.
>

    As Herny pointed out, you have to develop the thruster.
Also, while much lighter, you still have to lift the mass of
the thruster to orbit, and then the thruster lifts its own
weight into a higher orbit.  And you take up room in the payload
bay.

>pat

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

Date: 29 Apr 1993 11:34 CDT
From: [e-mail]
Subject: HyperKnowledge
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Georg Tuparev) writes...
>
>
>ANNOUNCEMENT:    The "HyperKnowledge" PROJECT for NeXTSTEP
>
>Motivation
>
>We are a heterogeneous group of scientists and students who feel that our
>work is continuously hindered by computer environments dominated by
>incompatible scientific tools and monstrous software packages (too often
>claiming to do everything).

>What we need is an object-oriented scientific environment where the tools
>we choose to use are integrated without being parts of a closed system,
>highly interactive, and extendable (both by the addition of our own
>specialized objects and by combining the available tools - graphically).
>The use of such an environment should be a natural extension of our work,
>requiring a very short learning phase and practically no
>user-documentation.


I know this is kinda off the subject of sci.space, but not really, I want to
answer this for their, as well as everyone else's information.  What these
people are proposing, by and large already exists and can be purchased today.

It is called labview by National Instruments.  IT is a wonderful object
oriented graphical programming language.  IT has been implemented on
both Mac's PC's and VME unix boxes.  IT is fare superior to any programming
approach that I have ever seen and allowed us to decrease the software
development time for our shuttle payloads by 90 percent.  This program is
not dependendant on specific hardware and already has exensive analysis
capability.

Why re-invent the wheel on a platform that may not exist? It is a great
idea but look out there at what is available today.  The Hydrogen leak on
the Shuttle was found using this software. All SSME control and simulation
studies, along with the real testing at MSFC is handled with LabVIEW.  There
are tons of applications, with the ability to create "virtual" instruments
that can accomplish any specific custom task the maker desires.  With the
addition of IEEE-488 support, the computer becomes a virtual control station,
allowing the graphic representation of remote instrumentation. With serial
I/O support that instrument can be anywhere.  The ground control software
for the main control of SEDSAT 1 will utilize this approach.

Dennis, University of Alabama in Huntsville

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

Date: Thu, 29 Apr 1993 13:26:31 GMT
From: "Daniel M. Newman" <[e-mail]>
Subject: Lindbergh and the moon (was:Why not give $1G)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Phil G. Fraering) writes:
>[e-mail] (Gregory N. Bond) writes:
>
>>In article <[e-mail]> [e-mail] (Josh Hopkins) writes:
>
>>   [re: voyages of discovery...]
>>   Could you give examples of privately funded ones?
>
Much of Cook's later exploration was privately funded, by Joseph Banks
among others (eg in Resolution & the earlier Endeavour).  Colnett's voyage
to the Galapagos was substantially privately funded by the owners of
British whaling vessels.  Chancellor and Willoughby were privately funded
by London merchant companies in their voyages to Muscovy.  The list is
almost endless.  Those doing the funding were about eighty percent
motivated by potential profit, ten percent by potential glory and ten
percent by the desire to advance the sum of human knowledge.

--
Dan Newman
Aeronautical Engineering
University of Sydney
Sydney NSW 2050
AUSTRALIA
From: [e-mail] (Daniel M. Newman)
Path: key3.ae.su.oz.au!dan
Newsgroups: sci.space
Subject:
Expires:
References:
Sender:
Reply-To: [e-mail] (Daniel M. Newman)
Followup-To:
Distribution: world
Organization: Aeronautical Engineering, Sydney University
Keywords:

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

Date: Thu, 29 Apr 1993 06:43:47 GMT
From: Ward Paul <[e-mail]>
Subject: Long term Human Missions
Newsgroups: sci.space,sci.space.shuttle,sci.astro

In article <[e-mail]> rek@siss81 (Robert Kaye) writes:
>
>Just a few contributions from the space program to "regular" society:
>
>1.    Calculators
>2.    Teflon (So your eggs don't stick in the pan)
>3.    Pacemakers (Kept my grandfather alive from 1976 until 1988)

I don't think touting contributions is a good idea.  World War II produced
many many beneficial spinoffs.  Eg. Radar, jet aeroplanes, rocket technology.
I don't think anyone would argue that World War II was, in and of itself,
a good thing.

If you want people to back the space program it must be a good thing in
and of itself.
--
Paul

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

Date: Thu, 29 Apr 1993 08:18:55 GMT
From: Peter J Card <[e-mail]>
Subject: Vandalizing the sky.
Newsgroups: sci.astro,sci.space

In <1rls95$[e-mail]> [e-mail] (Pat) writes:
>Planes  ruin the night sky.  Blimps ruin the night sky.  Radio towers
>ruin the night sky.

>Like i said,  get a vote, and create some more national parks.  which
>include onobstructed air space.

You should have heard Prof. McNally , from my days as an astronomy
undergraduate, denouncing photon pollution. It was easy to imagine him
taking practical steps to modify the sodium lamps on the street
outside Mill Hill observatory with a 12-gauge shotgun :-)

However, seriously, it is possible to limit the effects of
streetlights, by adding a reflector, so that the light only
illuminates the ground, which is after all where you need it. As a
bonus, the power consumption required for a given illumination level
is reduced. Strangely enough, astronomers often seek to lobby elected
local authorities to use such lighting systems, with considerable
success in the desert areas around the major US observatories. At
least, thats what McNally told us, all those years ago.
( British local authorities couldn`t care less, as far as I can see )

I suppose that the "right" to dark skies is no more than an aspiration,
but it is a worthwhile one. Illuminated orbital billboards seem especially
yukky, and are presumably in the area of international law, if any, although
I do find the idea of a right to bear anti-satellite weapons intriguing.
--
__._____.___._____.__._______________________________________________________
__|_. ._| ._|_._._|__| Peter Card, Joint European Torus, Abingdon
    | | | |_. | |    | Oxfordshire OX14 3EA UK. tel [phone] FAX 464404
    | | |  _| | |    | email [e-mail] or compuserve 100010,366
  ._| | | |_. | |    | It wasnt me. It was the others. They made me do it.
--`--~'-+---+-+-+----+-------------------------------------------------------
- Disclaimer: Please note that the above is a personal view and should not
  be construed as an official comment from the JET project.

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

Date: Thu, 29 Apr 1993 15:08:08 GMT
From: [e-mail]
Subject: Vandalizing the sky.
Newsgroups: sci.astro,sci.space

In article <1rls95$[e-mail]>, [e-mail] (Pat) writes:
> In article <[e-mail]> [e-mail] (George F. Krumins) writes:
> |I say:
> |What I'm objecting to here is a floating billboard that, presumably,
> |would move around in the sky.  I, for one, am against legislating
> |at all.  I just wish that people had a bit of common courtesy, and
> |would consider how their greed for money impacts the more ethereal and
>>aesthetic values that make us human.  This includes the need for wild
>>and unspoiled things, including the night sky.
>
>
> Sorry that's an aesthetics argument.  maybe this string shoudl mofe to
> sci.space.aesthetics.
>
> Planes  ruin the night sky.  Blimps ruin the night sky.  Radio towers
> ruin the night sky.
>
> Like i said,  get a vote, and create some more national parks.  which
> include onobstructed air space.
>
>

Hokay - I am hereby voting my backyard to be a sanctuary - one acre
where I can object to anything I do not like for aesthetic reasons.
<::-)  What a relief to know we both can be happy.

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

Date: Thu, 29 Apr 1993 12:23:12 GMT
From: Paul Dietz <[e-mail]>
Subject: What planets are habitable
Newsgroups: sci.space

> I would appreciate any thoughts on what makes a planet habitable for
> Humans.  I am making asumptions that life and a similar atmosphere
> evolve given a range of physical aspects of the planet.  The question
> is what physical aspects simply disallow earth like conditions.

This is a good question.  There are major blind spots in our understanding
of what makes the earth habitable.  For example, why does the earth's
atmosphere have the concentration of oxygen it does?  The naive
answer is "photosynthesis", but this is clearly incomplete.  Photosynthesis
by itself can't make the atmosphere oxygenated, as the oxygen produced
is consumed when the plants decay or are eaten.  What is needed
is photosynthesis plus some mechanism to sequester some fraction of
the resulting reduced material.

On earth, this mechanism is burial in seafloor sediments of organic
matter, mostly from oceanic sources.  However, this burial requires
continental sediments (in the deep ocean, the burial rate is so slow
that most material is consumed before it can be sequestered).

This suggests that a planet without large oceans, or a planet without
continents undergoing weathering, will have a hard time accumulating
an oxygen atmosphere.  In particular, an all-ocean planet may have a
hard time supporting an oxygen atmosphere.

There is also the problem of why the oxygen in the earth's atmosphere
has been relatively stable over geological time, for a period at least
2 orders of magnitude longer than the decay time of atmospheric O2 to
weathering in the absence of replenishment.  No convincing feedback
mechanism has been identified.  Perhaps the reason is the weak
anthropic principle: if during the last 500 MYr or so, the oxygen
level had dropped too low, we wouldn't be here to be wondering about
it.

    Paul F. Dietz
    [e-mail]

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

End of Space Digest Volume 16 : Issue 504
------------------------------