[X] My Assistant

[ljk4-1]

Paper: astro-ph/0512445

Date: Fri, 16 Dec 2005 17:56:49 GMT (76kb)

Title: Planetary catastrophe risks cannot generally be inferred from the
Earth's formation date

Authors: Adrian Kent (Department of Applied Mathematics and Theoretical
Physics, University of Cambridge)

Comments: 2 pages
\\
Tegmark and Bostrom's provocative analysis of the chances of a "doomsday
catastrophe" [Nature 438, 754 (2005)] sets out an interesting idea, but
unfortunately contains a fundamental error which invalidates their conclusions.
The essential problem with their argument can be seen by considering the
assertion that "if [planet-destroying] catastrophes were very frequent, then
almost all intelligent civilisations would have arisen much earlier than ours".
This does not follow from Tegmark and Bostrom's assumptions.

\\ ( http://arXiv.org/abs/astro-ph/0512445 , 0kb)

[ljk4-1]

MONDAY, DECEMBER 19, 2005 - NGC

Naked Science: "Birth of the Earth" at 9P et/pt

How did Earth evolve to support such a diversity of living creatures,
including humans, requiring special living conditions to survive? An
imaginary "human" time traveler takes us on a journey back to the
moment our solar system was born.

Watch a preview.

http://ng.chtah.com/a/tBDpv6HASJ4TXAbRKOPA...R.ASJ-RO8d/ngs2


Naked Science: "Super Volcano" at 10P et/pt

A super volcano explosion is a million times stronger than the
atomic bombing of Hiroshima. Scientists have discovered an active
super volcano under Yellowstone National Park. What would happen
if it erupted? Could the United States survive?

[tty]

fungi? Yes they can. At a similar state of evolution, we were not better. Given equal chances, they may have evolved in intelligent beings.

Seriously, what, I think, gave the advantage to bilateralians is not the bilateral symmetry by itself, it is a set of innovations the other were deprived, such as nervous cells, or the coelome (sorry this is the latin name I don't know in english) or closed inner body cavity which allowed all the building of further evolution. The lombrics can move thank to coelomes (one per ring), and we still have three body cavities (or lombric-like rings) separated by muscles: chest, belly, and a smaller perinear cavity.  Fungi seriously lack such structures, and corals have an open boby cavity for feeding (the opening serving ans both mouth and anus).

These body structures were first coded by a series of adjacent genes, called homeobox, each one coding for a body segment, and controling the growth of each segment. Further evolution complexified this scheme, but without altering the basic structure. It is the very unlikely appearance of such a complex structure which took many time and was the real breakthrough which allowed bilateralians to be the first. As such an event is rare, it does not happens often, only once in Earth history, and it is likely not to happen again, as the bilateralians now hamper any further evolution of the other clades.

beings like fungi are multicellular, but they don't have a homeobox-like system, and other system such as specialized cells. This allow them to grow rapidly, but with only simple structures.

Sime dates for Earth history:
-multicellular beings are traced from -600 millions years and likely existed 1 billion years ago
-bilateralians are known since 600 millions years only.

Actually Hox genes are not specific to Bilateria since Cnidarians also have them, though only two each (homologous to the anterior and posterior Hox groups of e. g. arthropods). Sponges do lack Hox genes.

Multicellular organisms (algae) are known bact to at least 1200 mya (million years ago). Bilateria are known back to about 600 mya (earliest Edicaran faunas), but molecular data suggest they are at least 100 my older. This incidentally means that they originated at about the time of the extreme Neoproterozoic glaciations which may have turned Earth into a "snowball", or nearly so. The mass extinction these must have caused may have "made way" for new life-forms, including ultimately us.

tty

[Guest_Richard Trigaux_*]

Actually Hox genes are not specific to Bilateria since Cnidarians also have them, though only two each (homologous to the anterior and posterior Hox groups of e. g. arthropods). Sponges do lack Hox genes.

Multicellular organisms (algae) are known bact to at least 1200 mya (million years ago).  Bilateria are known back to about 600 mya (earliest Edicaran faunas), but molecular data suggest they are at least 100 my older.  This incidentally means that they originated at about the time of the extreme Neoproterozoic glaciations which may have turned Earth into a "snowball", or nearly so. The mass extinction these must have caused may have "made way" for new life-forms, including ultimately us.

tty

Thank you tty for your interesting precisions.

(For people not informed, I recall here the extreme climate changes which happened on Earth 600 million years ago. At that time, the continents were gathered along the equator, lefting place for two large polar oceans. This situation allowed a climate trick: large parts of this ocean were freezing in winter, and, as ice reflects most of sun heat, it cooled the climate. This process went increasing and increasing, until all the Earth was frozen, with ice all over the oceans and glaciers on the continents. Fortunatelly volcanoes were still emitting carbon dioxid, increasing greenhouse effect until the temperature increased enough to revert the icing process and melt all the ice. But at that time Earth had suddenly to sustain very high temperatures, 50°C or more, untill the self-regulation of temperature operated, bringing back Earth to a more ordinary temperature. This balance happened several times, making many oceanic form of life disappear. There was no life on the continents at this time.)

What I think is that it is the very evolution of the Hox sytem which produced all the clades, bilateralians, cnidarians, etc.
Bacteria have only genes which react to various chemical conditions to sustain the life of the bacteria. Primitive multicellular had system reacting to external chemical signals to trigger various sets of behaviour for the cell. This is enough for primitive multicellular, mushrooms, sponges, etc. which get their shapes from the grow process, like a mathematical rule can grow shapes in a fractal game.
But to have a real body structure needs 1)a kind of "map" of this structure, 2)coding various sets of behaviours from the cells, 3)a mean to specialize cells. These multiple conditions explain why about 500 million years were necessary to pass from simple masses of jelly to really organized bodies. But it was a necessary result of many simpler steps, the evidence is that plants evolved in a similar way and time, although in complete independence from animals.

The basic map was the Hox system, and we can say, I think, that it is the very process of appearance and setting of this Hox system which created all the clades.
Further steps gave the advantage to bilateralians, such as the coelome (closed inner body cavity) which allowed for real movement, not just swimming with a flagela like cnidarian larvae.

That all this happened into a period of extreme climate stress also tells us that such catastrophes (meteorite impacts, climate change) are an accelerator of evolution. A simple Darwinian view (as Darwin himself observed) implies slow processes which make two species of one specie separated in two populations. But more modern views suggest that there was many "punctuations", short periods of accelerated evolution, when a few number of individuals are constrained to find innovating solutions to an environment change. Humans themselves are the descendants of a very little groups of individuals, perhaps some hundreds, or even less.

Of course if such a global freezing occured today, 500 million years of evolution would be lost. Or there would be very few survivors, but what would be the result?

[Guest_Richard Trigaux_*]

Paper: astro-ph/0512445

Date: Fri, 16 Dec 2005 17:56:49 GMT  (76kb)

Title: Planetary catastrophe risks cannot generally be inferred from the
  Earth's formation date

Authors: Adrian Kent (Department of Applied Mathematics and Theoretical
  Physics, University of Cambridge)

Comments: 2 pages
\\
  Tegmark and Bostrom's provocative analysis of the chances of a "doomsday
catastrophe" [Nature 438, 754 (2005)] sets out an interesting idea, but
unfortunately contains a fundamental error which invalidates their conclusions.
The essential problem with their argument can be seen by considering the
assertion that "if [planet-destroying] catastrophes were very frequent, then
almost all intelligent civilisations would have arisen much earlier than ours".
This does not follow from Tegmark and Bostrom's assumptions.

\\ ( http://arXiv.org/abs/astro-ph/0512445 ,  0kb)

hmmm...
The effect of planetary catastrophes ending any life on a planed much depends on if this catastrophe occurs only on a planet (impact, climate, star death, gamma ray bursts sending beams...) of if a catastrophe can really end up life in all a galaxy (large gamma ray bursts spreading death all around them).

That a gamma ray bursts sterilized our own galaxy certainly not happened since at least the formation of our planet (otherwise we should not be here). But it could have happened just before. If so, we can expect to find only younger or equally old inhabited planets. In this model the probability of an inhabited planed decreases sharply with ages superiors to 4-5 billion years. If we were slow, there could be many civilizations. If we were faster, there could be few or not.

Other types of more local catastrophes imply that the probability to find an inhabited planet in a given system decreases with the age of the system, in a monotonous way. That too implies that this probability decreases with the achieved level of evolution. But in this case we are more likely to find an intermediate number of civilization.

As we can see, we are getting parts of the puzzle of the Drake equation, but we still lack far too many to be able to assess figures, even extreme (between billions of civilizations and only one). How to get out of this? With theoretical studies of the evolution of planetary systems and planet climate, and also, with observation, such as above, with the spectroscoping study of signature of evolved life on planets. SETI already bite into the error box, in detecting no large network of powerful civilizations.

[ljk4-1]

Partial Ingredients for DNA and Protein Found Around Star

NASA’s Spitzer Space Telescope has discovered some of life’s most basic ingredients in the dust swirling around a young star. The ingredients – gaseous precursors to DNA and protein – were detected in the star’s terrestrial planet zone, a region where rocky planets such as Earth are thought to be born.

The findings represent the first time that these gases, called acetylene and hydrogen cyanide, have been found in a terrestrial planet zone outside of our own.

"This infant system might look a lot like ours did billions of years ago, before life arose on Earth," said Fred Lahuis of Leiden Observatory in the Netherlands and the Dutch space research institute called SRON. Lahuis is lead author of a paper to be published in the Jan. 10 issue of the Astrophysical Journal Letters.

http://www.spitzer.caltech.edu/Media/relea...6/release.shtml

[deglr6328]

I think its JUST a bit of a stretch to say that partial ingredients for DNA and protein were found when really all they found was HCN and C2H2. Almost like saying "environment suitable for polar bear habitat found on Enceladus"! Interesting nonetheless though.

[Guest_Richard Trigaux_*]

I think its JUST a bit of a stretch to say that partial ingredients for DNA and protein were found when really all they found was HCN and C2H2. Almost like saying "environment suitable for polar bear habitat found on Enceladus"! Interesting nonetheless though.

I think that our actual DNA and proteins components are not necessarily the only solution for life; but they appeared as they appeared because they were created from available compounds, which themselves appeared from basic compounds like HCN and C2H2 because they were first available. But, of course, as you say, there are many steps between HCN and life, and the first does not necessarily implies the later, many other conditions are needed. But this observation is interesting, because it shows that the very first prerequisites for the appearance of life (accretion disk temperature and chemistry) are very common (if not mandatory) in solar systems, giving a very high value to the first term of the Drake equation.

[Guest_Richard Trigaux_*]

Back to the idea of gamma ray bursts (GRB) able to sterilize a whole galaxy.

First, even if GRBs are really dangerous, I have some doubts that they are really able to sterilize a whole galaxy.

Second, I note that GRBs occured in a distant past, perhaps at an epoch where the metallicity of stars was lower. As far as I know, the most recent GRBs are 3 billion years old, and the peak activity was 10 billions years ago. And they are not as numerous as we can think. (If we assume one detection per day, and 130 billion galaxies, that makes about 2.8 GRBs per billion years in a given galaxy, 10 billion years ago)

So we can figure this out: 10 billion years ago, GRBs were very numerous, and, if they were really able to sterilize a galaxy, this happened every 360 million years in average, much too short a time to allow for evolved life to appear.
But the activity of GRBs gradually subsided, and is quasi-zero today. So we may find most galaxies where there was no GRBs since 3, or 5, see 7 billion years.

Applied to our galaxy, this makes about the age of the Earth, and an elegant solution to the black sky paradox (life is expected to appear on many planets, but we yet detected no evolved civilizations): we would be amont the firsts to appear.

Places which are expected to have stopped any GRB activity for longer than our galaxy would be giant elliptic galaxies like Virgo. This is the best place to search for giant Type III civilizations (After kardanchev a Type III civilization is using the energy of its whole galaxy). So this is the place where we can more expect things like Dyson spheres, engineered stars, etc (if any such things can exist, but this is not what seems the most likely to me)

[ljk4-1]

On December 15 former Senator William Proxmire of Wisconsin died at the age of 90. Proxmire was no friend of the space program, and in 1979 he gave one his famous “golden fleece” awards for wasteful government spending to NASA for its research in the search for extraterrestrial intelligence (SETI). A few years later he was instrumental in stopping government support for SETI.

But Proxmire also provided The Planetary Society with one of its greatest victories, and consequently earned the respect of Carl Sagan and the organization for his willingness to listen.

The rest is here:

http://planetary.org/news/2005/1216_Societ...ETI_Critic.html

[Guest_Richard Trigaux_*]

On December 15 former Senator William Proxmire of Wisconsin died at the age of 90.   Proxmire was no friend of the space program, and in 1979 he gave one his famous “golden fleece” awards for wasteful government spending to NASA for its research in the search for extraterrestrial intelligence (SETI). A few years later he was instrumental in stopping government support for SETI.

But Proxmire also provided The Planetary Society with one of its greatest victories, and consequently earned the respect of Carl Sagan and the organization for his willingness to listen.

The rest is here:

http://planetary.org/news/2005/1216_Societ...ETI_Critic.html

For his punishment Mr Proxmire will be reincarnated on another planet.

Interesting article, ljk4-1. It tells us that even skeptics can be convinced when taught rationaly of what is going on.

Rest in Peace Mr Proxmire. And enjoy your new planet... Now where you are, if you want to help SETI, please... send us a signal.

[ljk4-1]

Astrophysics, abstract
astro-ph/0512204

From: Max Tegmark [view email]

Date (v1): Thu, 8 Dec 2005 05:17:15 GMT (21kb)

Date (revised v2): Wed, 21 Dec 2005 14:28:48 GMT (23kb)

How unlikely is a doomsday catastrophe?

Authors: Max Tegmark (MIT), Nick Bostrom (Oxford)

Comments: Substantially expanded discussion to better explain key argument. 4 pages, 1 fig

Numerous Earth-destroying doomsday scenarios have recently been analyzed, including breakdown of a metastable vacuum state and planetary destruction triggered by a "strangelet'' or microscopic black hole. We point out that many previous bounds on their frequency give a false sense of security: one cannot infer that such events are rare from the the fact that Earth has survived for so long, because observers are by definition in places lucky enough to have avoided destruction. We derive a new upper bound of one per 10^9 years (99.9% c.l.) on the exogenous terminal catastrophe rate that is free of such selection bias, using planetary age distributions and the relatively late formation time of Earth.

http://arxiv.org/abs/astro-ph/0512204

[ljk4-1]

Paper: astro-ph/0512561

Date: Thu, 22 Dec 2005 13:45:36 GMT (241kb)

Title: Photodissociation of organic molecules in star-forming regions II:
Acetic acid

Authors: S. Pilling (1 and 2), A. C. F. Santos (3) and H. M. Boechat-Roberty
(1) ((1) OV-UFRJ, (2) IQ-UFRJ, (3) IF-UFRJ)

Comments: Comments: 8 pages, 5 figures, 3 tables. Accepted to be printed in A&A
\\
Fragments from organic molecule dissociation (such as reactive ions and
radicals) can form interstellar complex molecules like amino acids. The goal of
this work is to experimentally study photoionization and photodissociation
processes of acetic acid (CH$_3$COOH), a glycine (NH$_2$CH$_2$COOH) precursor
molecule, by soft X-ray photons. The measurements were taken at the Brazilian
Synchrotron Light Laboratory (LNLS), employing soft X-ray photons from a
toroidal grating monochromator (TGM) beamline (100 - 310 eV). Mass spectra were
obtained using the photoelectron photoion coincidence (PEPICO) method. Kinetic
energy distribution and abundances for each ionic fragment have been obtained
from the analysis of the corresponding peak shapes in the mass spectra.
Absolute photoionization and photodissociation cross sections were also
determined. We have found, among the channels leading to ionization, that only
4-6% of CH$_3$COOH survive the strong ionization field. CH$_3$CO$^+$, COOH$^+$
and CH$_3^+$ ions are the main fragments, and the presence of the former may
indicate that the production-destruction process of acetic acid in hot
molecular cores (HMCs) could decrease the H$_2$O abundance since the net result
of this process converts H$_2$O into OH + H$^+$. The COOH$^+$ ion plays an
important role in ion-molecule reactions to form large biomolecules like
glycine.

\\ ( http://arXiv.org/abs/astro-ph/0512561 , 241kb)

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

Paper: astro-ph/0512563
Date: Thu, 22 Dec 2005 14:11:29 GMT (946kb)

Title: Molecular gas in the Andromeda galaxy

Authors: Ch. Nieten (1), N. Neininger (1,2,3), M. Guelin (3), H. Ungerechts
(4), R. Lucas (3), E. M. Berkhuijsen (1), R. Beck (1), R. Wielebinski (1)
((1) MPI fuer Radioastronomie, Bonn, Germany, (2) Radioastronomisches
Institut, Univ. Bonn, Germany, (3) IRAM, Grenoble, France, (4) IRAM, Granada,
Spain)

Comments: 21 pages, 16 figures. Accepted for publication in A&A
\\
We present a new 12CO(J=1-0)-line survey of the Andromeda galaxy, M31,
covering the bright disk with the highest resolution to date (85 pc along the
major axis), observed On-the-Fly (in italics) with the IRAM 30-m telescope. We
discuss the distribution of the CO emission and compare it with the
distributions of HI and emission from cold dust traced at 175mum. Our main
results are: 1. Most of the CO emission comes from the radial range R=3-16 kpc,
but peaks near R=10 kpc. The emission is con- centrated in narrow, arm-like
filaments defining two spiral arms with pitch angles of 7d-8d. The average
arm-interarm brightness ratio along the western arms reaches 20 compared to 4
for HI. 2. For a constant conversion factor Xco, the molecular fraction of the
neutral gas is enhanced in the arms and decreases radially. The apparent
gas-to-dust ratios N(HI)/I175 and (N(HI)+2N(H2))/I175 increase by a factor of
20 between the centre and R=14 kpc, whereas the ratio 2N(H2)/I175 only
increases by a factor of 4. Implications of these gradients are discussed. In
the range R=8-14 kpc total gas and cold dust are well correlated; molecular gas
is better correlated with cold dust than atomic gas.

\\ ( http://arXiv.org/abs/astro-ph/0512563 , 946kb)

[ljk4-1]

Paper: astro-ph/0512589
Date: Fri, 23 Dec 2005 05:42:54 GMT (218kb)

Title: A CH3CN and HCO+ survey towards southern methanol masers associated with
star formation

Authors: C. R. Purcell, R. Balasubramanyam, M. G. Burton, A. J. Walsh, V.
Minier, M. R. Hunt-Cunningham, L. L. Kedziora-Chudczer, S. N. Longmore, T.
Hill, I. Bains, P. J. Barnes, A. L. Busfield, P. Calisse, N. H. M. Crighton,
S. J. Curran, T. M. Davis, J. T. Dempsey, G. Derragopian, B. Fulton, M. G.
Hidas, M. G. Hoare, J.-K. Lee, E. F. Ladd, S. L. Lumsden, T. J. T. Moore, M.
T. Murphy, R. D. Oudmaijer, M. B. Pracy, J. Rathborne, S. Robertson, A. S. B.
Schultz, J. Shobbrook, P. A. Sparks, J. Storey, T. Travouillion

Comments: 29 pages, 16 figures. Accepted for publication in MNRAS. For
associated online figures please see

http://www.phys.unsw.edu.au/~crp/papers/cp...2005_online.pdf

\\
We present the initial results of a 3-mm spectral line survey towards 83
methanol maser selected massive star-forming regions. Here we report
observations of the J=5-4 and 6-5 rotational transitions of methyl cyanide
(CH3CN) and the J=1-0 transition of HCO+and H13CO+.

CH3CN emission is detected in 58 sources (70 %) of our sample). We estimate
the temperature and column density for 37 of these using the rotational diagram
method. The temperatures we derive range from 28-166 K, and are lower than
previously reported temperatures, derived from higher J transitions. We find
that CH3CN is brighter and more commonly detected towards ultra-compact HII
(UCHII) regions than towards isolated maser sources. Detection of CH3CN towards
isolated maser sources strongly suggests that these objects are internally
heated and that CH3CN is excited prior to the UCHII phase of massive
star-formation.

HCO+ is detected towards 82 sources (99 % of our sample), many of which
exhibit asymmetric line profiles compared to H13CO+. Skewed profiles are
indicative of inward or outward motions, however, we find approximately equal
numbers of red and blue-skewed profiles among all classes. Column densities are
derived from an analysis of the HCO+ and H13CO+ line profiles.

80 sources have mid-infrared counterparts: 68 seen in emission and 12 seen in
absorption as `dark clouds'. Seven of the twelve dark clouds exhibit asymmetric
HCO+ profiles, six of which are skewed to the blue, indicating infalling
motions. CH3CN is also common in dark clouds, where it has a 90 % detection
rate.

\\ ( http://arXiv.org/abs/astro-ph/0512589 , 218kb)

[ljk4-1]

Pulsars as Beacons for SETI

Abstract: This paper proposes that pulsars can serve as beacons for the discovery of and communication with extraterrestrials. The motivation for the communication strategy proposed is discussed in detail, along with relevant astrophysical considerations.

It is shown that millisecond pulsars have characteristics and a distribution in space that make it possible to envisage communication being targeted towards and away from habstars (as defined by Turnbull & Tarter) aligned with pulsars in a
specified way. Lists of candidate habstars and their pulsar alignments are included for those wishing to conduct searches using the strategy described.

http://www.cs.bham.ac.uk/~whe/SETIPaper.pdf

The author of the above paper received 30 hours of time on the Arecibo Radio Telescope to gather data for his SETI concept. You can read the proposal here:

http://www.cs.bham.ac.uk/~whe/AOproposal.pdf

More information here:

http://www.cs.bham.ac.uk/~whe/CETI.html