Mirror image molecules in Orion

31/07/2010

Pick of the Pics and Updating Magic Universe

Mirror-image molecules sorted in the Orion Nebula

But Pasteur’s hope for a cosmic driver comes true only locally

A predominance of either left-handed or right-handed versions of molecules is likely within huge dust clouds imaged by Japanese astronomers. The electric field of light rays coming from the clouds corkscrews to the left or corkscrews to the right, with “circular polarization”. The different kinds of clouds are clearly distinguishable in a massive star-forming region within the Orion Nebula, called BN/KL. Yellow denotes left-handed light, and red, right-handed. The largest yellow and red features are about 100 times wider than the Solar System, and the astronomers suggest that the polarized light will favour the formation of left-handed or right-handed molecules. The conspicuous dots left of centre near the bottom are bright young stars of the Trapezium group — strong winds  from which have helped the astronomers by blowing away dust that otherwise would obscure the BN/KL region of interest. Credit: Near-infrared (2.14 μm) image with the SIRPOL polarization instrument, NAOJ.

On seeing this report by Tsubasa Fukue and Motohide Tamura of the National Astronomical Observatory of Japan (with colleagues in Japan, UK, Australia and USA) my mind went straight back to Louis Pasteur.

Alanine, an amino acid, has mirror-image forms. L (laevo) rotates the electric field of light to the left and and D (dextro) to the right. Image NAOJ.

Although immortalized for the germ theory of disease, Pasteur’s initial claim to fame came from a discovery he made as a young student – namely that molecules from living sources have effects on the polarization of light, but the same molecules made synthetically do not. This is the phenomenon of chirality, or handedness. Chemists had to learn to think three-dimensionally about versions of molecules that are mirror images of each other. In the example shown here, every amino acid molecule in living things on Earth is of the left-handed (L) kind.

Molecular handedness is a fundamental feature of life and Pasteur suspected that some fundamental feature of the Universe was responsible for it. The phenomenon has been both a puzzle and a spur for investigators of the origin of life. The fact that carbon compounds in meteorites show the same bias in handedness as that seen on Earth suggests that some physical process was at work throughout the Solar System, at least.

The astronomers now offer an answer. Circularly polarized light pervading the dust cloud in which the Sun and its planets were born would have prompted our molecular bias. The scenario is made convincing by the sheer size of the clouds in Orion possessing one polarity or the other. But it ‘s not the Universe-wide mechanism that Pasteur expected. It seems that if the Solar System had originated in a cloud with the opposite kind of circularly polarized light, all our amino acids would be dextro.

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Comets and life 4

05/06/2010

Updating Comets and Magic Universe

Did comets spark life on Earth?

Part 4: Life footloose in space

In Part 1 of this series, I mentioned that in Comets, written 30 years ago, I made fun of propositions from the astrophysicists Fred Hoyle and Chandra Wickramasinghe about viable entities living in comets and being delivered ready-made to the Earth, scattered from the comets’ tails. What follows fulfils a promise to look at Chandra’s present ideas — I hope with an open mind.

To back-track a little, there’s a 100-year history of eminent scientists, driven by despair about explaining the very improbable chemistry of life by home cooking on the Earth, suggesting that life came from elsewhere. Of course, their scenarios didn’t explain the origin of life, they merely transferred it somewhere else. Out of sight, out of mind, perhaps.

  • 1907 Svante Arrhenius (yes, the CO2 warming pioneer) suggested that bacterial spores escaped from an alien planet, were driven through interstellar space by the pressure of sunlight, and revived when they reached the Earth.
  • 1971 Francis Crick (yes, of DNA fame) with Leslie Orgel proposed that intelligent beings in another part of the Galaxy spotted the Earth as a suitably wet planet and sent bacteria in a spaceship to seed it.
  • 1979 Fred Hoyle (yes, celebrated for the origin of the elements) with Chandra Wickramasinghe said that life on Earth began in comets, and diseases still come from them.

It was hard not to chuckle over their book Diseases from Space, because Hoyle and Wickramasinghe’s account filled the sky with germs, in a distant echo of the old superstition that comets portended plagues.

John Gadbury (1665) linked comets and catastrophes -- "Famine, Plague & Warrs" In actuality, bubonic plague afflicted London following the depicted 1664-5 comet. Obtained from the Royal Astronomical Society, this is an illustration in N. Calder, Comets: Speculation and Discovery.

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Comets and life 3

04/06/2010

Updating Comets and Magic Universe

Did comets spark life on Earth?

Part 3 Initiating biochemical action

Pascale Ehrenfreund rides again (as in Part 2) in the story in Magic Universe called “Life’s origin: will the answer to the riddle come from outer space?”. But please focus first on Wlodzimierz Lugowsky.

I can trace my ancestry back to a protoplasmal primordial atomic globule,’ boasts Pooh-Bah in The Mikado. When Gilbert and Sullivan wrote their comic opera in 1885 they were au courant with science as well as snobbery. A century later, molecular biologists had traced the genetic mutations, and constructed a single family tree for all the world’s organisms that stretched back 4 billion years ago, to when life on Earth probably began. But they were scarcely wiser than Pooh-Bah about the precise nature of the primordial protoplasm.

In 1995 Wlodzimierz Lugowsky of Poland’s Institute of Philosophy and Sociology wrote about ‘the philosophical foundations of protobiology’. He listed nearly 150 scenarios then on offer for the origin of life and, with a possible single exception to be mentioned later, he judged none of them to be satisfactory. Here is one of the top conundrums for 21st Century science. The origin of life ranks with the question of what initiated the Big Bang, as an embarrassing lacuna in the attempt by scientists to explain our existence in the cosmos.

After discussing possible “home cooking” of life by hypercycles, RNA catalysis or lipid catalysis, and touching on the possibility of false starts, the tale turns back to the sky in pursuit of the only hypothesis acceptable to Lugowsky.

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Comets and life 2

01/06/2010

Updating Comets and Magic Universe

Did comets spark life on Earth?

Part 2: Cosmic carbon compounds

An earlier post, Part 1 under this heading, commented enthusiastically but briefly on a French team’s find of extraterrestrial dust grains rich in carbon in the snow of Antarctica. https://calderup.wordpress.com/2010/05/10/comets-and-life/

I promised more to come, and here it begins. Part 2 deals with cosmic carbon compounds. Later, Part 3 will reconsider the initiation of biochemical action, and Part 4 will look at suggestions of natural life footloose in space.

There were far more comets around when the Solar System was young, in the “heavy bombardment” phase of Earth history lasting until 3.8 billion years ago. Water is abundant in interstellar space and available to build the icy nuclei of comets. Comets may have delivered most of the Earth’s surface water, essential for life.

Carbon compounds are the other main ingredient for life. Comets’ tails consist mainly of small dust grains released from the nuclei, including grains laden with carbon compounds that may have contributed to the origin of life on the Earth. Here’s a general impression of important “prebiotic” molecules made in the vicinity of dying stars and newborn stars and available for incorporation into comets.

PAHs, polyaromatic hydrocarbons observable in interstellar space, could be ancestral to the aromatic compounds that have the very smell of life. Illustration from Pascale Ehrenfreund & Steven Charnley, 2000 – see reference. Graphic art: ©2000 R. Ruiterkamp


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