12 April 2007

Kleine außerirdische Farbenlehre, nur für den Fall...

Mit den heutigen Möglichkeiten ist die direkte Beobachtung extrasolarer (außerhalb unseres Sonnensystems befindlicher), "erdähnlicher" Planeten im Orbit um sonnenähnliche Sterne ausgeschlossen, da das von ihnen reflektierte Licht von dem der Lichtquelle (des Sterns) bei weitem überstrahlt wird. In einem Artikel in der aktuellen Nature-Ausgabe wird ein Teleskop-Modell vorgestellt, das diese technische Schwierigkeit überwinden könnte.
The detection and characterization of an Earth-like planet orbiting a nearby star requires a telescope with an extraordinarily large contrast at small angular separations. At visible wavelengths, an Earth-like planet would be 1 times 10-10 times fainter than the star at angular separations of typically 0.1 arcsecond or less. There are several proposed space telescope systems that could, in principle, achieve this. Here we report a laboratory experiment that reaches these limits. We have suppressed the diffracted and scattered light near a star-like source to a level of 6 times 10-10 times the peak intensity in individual coronagraph images. In a series of such images, together with simple image processing, we have effectively reduced this to a residual noise level of about 0.1 times 10-10. This demonstrates that a coronagraphic telescope in space could detect and spectroscopically characterize nearby exoplanetary systems, with the sensitivity to image an 'Earth-twin' orbiting a nearby star.
[Quelle: Trauger JT & Traub WA. A laboratory demonstration of the capability to image an Earth-like extrasolar planet. Nature 446, 771-773 (12 April 2007)]

Von daher machen auch Überlegungen wie die folgende einen Sinn: Wie würden Photosynthese-betreibende "Pflanzen" auf anderen Planeten aussehen?
Nancy Kiang*, a biometeorologist at the NASA Goddard Institute for Space Studies in New York, modelled the solar and atmospheric conditions of other planets to see which ones might be suitable for photosynthetic life, and what those photosynthesizers might look like.

Red dwarfs, for example, emit only a fraction of the visible light produced by our own Sun, meaning that plants on planets around these stars will probably hoard all the visible light they can absorb, rather than reflecting back any particular wavelength, Kiang hypothesizes. That means they would probably look black.

[...]Earth already provides a variety of colours and pigments to chose from — from the comforting greens of our land plants to the dull purples of some photosynthetic bacteria, and the jarring reds of certain seaweeds.

The colour reflected by each of these organisms is made up of the wavelengths that the photosynthesizer has shunned — typically those that are not particularly useful for them. The colour of a plant, therefore, can depend on the quality of light the plant receives and that, in turn, depends on the properties of the local sun and the atmosphere that filters out the sun's rays.

The sunlight that strikes Earth's surface, for example, is rich in green light, but land plants often shun this seemingly rich source of energy. [...] But green light is not as rich in photons as red light and not as energetic as blue light. So although plants seem to have wasted energy by not harnessing the abundant greens, Kiang thinks that they've just focused their efforts on the more nutritious reds and blues.

The team thinks that all plants will be keen to suck up high-energy blue light — so that rules out bright blue leaves.[...]

Telescopes can't yet see the colours of far-flung rocky planets, but the team hopes that their work can be used to design instruments that can detect the spectral signatures characteristic of photosynthetic life. Their model helps to show which wavelengths plants on various planets would be most likely to absorb, creating a custom signature for life for different planetary situations.
[Quelle & Bild-Quelle: Ledford. Alien plants may come in all colours but blue. News@Nature]

Was ist eigentlich die kreationistische Einstellung zu außerirdischem Leben?

Wobei, wenn morgen veröffentlicht würde, dass Leben auf einem anderen Planeten gefunden wurde, gäbe es wohl auch nur die üblichen Reaktionen: Leugnen, Goddidit und/oder Freie Assoziation von Bibelstellen, bis eine gefunden ist, die man so interpretieren könnte, als wäre das mit dem außerirdischen Leben dem Autor schon bekannt gewesen....


* Kiang N. Y., et al. Spectral signatures of photosynthesis. I. Review of Earth organisms. Astrobiology, 7 . 222 - 251 (2007).
Kiang N. Y., et al. Spectral Signatures of Photosynthesis. II. Coevolution with Other Stars And The Atmosphere on Extrasolar Worlds.
Astrobiology, 7 . 252 - 274 (2007).

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