Galactic Habitable Zones and Possibility of Carbon-Water Based Life

Ultraviolet (UV) photons harm the DNA molecule...

Image via Wikipedia

Galactic habitable zones have much significance if we are searching a habitable planet to colonize or even we want to contact carbon water based intelligence.

The centerpiece of all life on Earth is carbon-based biochemistry. It has repeatedly been surmised that biochemistry based on carbon may also play a pivotal role in extraterrestrial life forms, if existent. This is due to the pronounced advantages of carbon, especially compared to its closest competitor (i.e., silicon), which include: its relatively high abundance, its bonding properties, and its ability to form very large molecules as it can combine with hydrogen and other molecules as, e.g., nitrogen and oxygen in a very large number of ways (Goldsmith & Owen 2002). In a paper by M. Cuntz and L. Gurdemir, they explored the relative damage to carbon-based macro-molecules in the environments of stars other than the Sun using DNA as a proxy. They focused on the effects of photospheric radiation from main-sequence stars, encompassing the range between F0 and M0. Their models consist of the following components:
1. The radiative effects on DNA are considered by applying a DNA action spectrum (Horneck 1995). It shows that the damage is strongly wavelength-dependent, increasing by more than seven orders of magnitude between 400 and 200 nm. The different regimes are commonly referred to as UV-A, UV-B, and UV-C. As wavelenth would decrease consequently its energy would increase. So it seems pretty obvious that it would cause more damage to DNA strands.
2.The planets are assumed to be located in the stellar habitable zone (HZ). Following the concepts by Kasting et al. (1993) and Underwood et al. (2003), they distinguished between the conservative and generalized HZ. The inner and outer edge of the conservative HZ are given by the onset of water loss and CO2 condensation, respectively, whereas the inner and outer edge of the generalized HZ are given by the runaway greenhouse effect and the breakdown of greenhouse heating, respectively, needed to permit the existence of fluid water on the planetary surface.
3. Stellar photospheric radiation is represented by using realistic spectra, which take into account millions or hundred of millions of lines for atoms and molecules (Castelli & Kurucz 2004, and related publications). Clearly, significant differences emerge between the different spectral types, both concerning the total amount of radiation and their spectral distribution.
4. They considered the effects of attenuation by a planetary atmosphere. The following cases are considered: Earth as today, Earth 3.5 Gyr ago, and no atmosphere at all.
[Image Details: It is clear from image that habitability is increasing towards left since biological damage is decreasing from right to left. They show the relative damage to DNA due to photospheric radiation from stars between spectral type F0 and M0. The results are normalized to today’s Earth, placed at 1 AU from a star of spectral-type G2V. We also considered planets at the inner and outer edge of either the conservative or generalized HZ as well as planets of different atmospheric attentuation.]
Now the conclusions which are obvious from the plots are mainly:
1.All main-sequence stars of spectral type F to M have the potential of damaging DNA due to UV radiation. The amount of damage strongly depends on the stellar spectral type, the type of the planetary atmosphere and the position of the planet in the habitable zone (HZ).
2. The damage to DNA for a planet in the HZ around an F-star (Earth- equivalent distance) due to photospheric radiation is significantly higher (factor 5) compared to planet Earth around the Sun, which in turn is significantly higher than for an Earth equivalent planet around an M-star (factor 180). Small modifications of this picture occur for different planetary positions inside their respective HZs.
3. Regarding the cases studied, they found that the damage is most severe in the case of no atmosphere at all, somewhat less severe for an atmosphere corresponding to Earth 3.5 Gyr ago, and least severe for an atmosphere like Earth today.
However, the final conclusion are well known to us even you are not going to study that research paper. The planet to where we re going to establish our future colonies, must have atmosphere and should be located in the proximity of M type stars.
[Ref: Astrobiology in the Environments of Main-Sequence Stars: Effects of Photospheric Radiation By M. Cuntz and L. Gurdemir]
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About bruceleeeowe
An engineering student and independent researcher. I'm researching and studying quantum physics(field theories). Also searching for alien life.

9 Responses to Galactic Habitable Zones and Possibility of Carbon-Water Based Life

  1. Rolf says:

    I thought we leave biology behind during this century, so why would we need to look for a habitable planet to support carbon/water life forms?

    • Tim says:

      [..]I thought we leave biology behind during this century, […]
      what that meant?

      • Rolf says:

        Well if the technological singularity comes, and I do think there is a lot of things going on in my eyes supporting that theory, we will improve our bodies and make version 2.0 and so on of our currently carbon/watter physiology. That will of course allow us human beings to survive in completely different environments than what biology requires. In that area the works of Robert Freitas give a glimps of what e.g. nanotechnology can do to improve human bodies not to speak of work on mind uploading to computers etc.. So I am questioning from a colonization point of view the need for earth like environments supporting carbon/water life forms.

        I have seen 3 estimates on the time horizon of the technological singularity, Vernor Vinge estimates latest 2030, Ray Kurzweil 2045 and John Smart estimates 2060. All of them are well in this century.

  2. bruceleeeowe says:

    Hi Rolf,
    we need to search for habitality zones to colonize it, providing the consideration to our future pervading civilizations. It would always be easy to colonize HZs. Except that we have some more probability to find our extraterrestrial brothers in earth like planets, as we know that every corner of Earth is filled with ubiquitous life.

  3. bruceleeeowe says:

    Robert Freitas has done a nice job in speculating the potential of nanotechnology. Seems like you are a huge fan of him. Indeed, nanotechnology could make us stronger against adverse conditions however it seems improbable it would ever be capable of changing chaotic metabolism of body. For example, it may provide you the way to live inside water but you still need oxygen to breathe, to empower your cells and to let your brain work properly. Nanotechnology can’t do anything for that. You would still need water to let blood remain liquid and for other purposes. Sure, nanotechnology could enhance your potential but can’t mutate you. That’s why we need to search for Earth like planets. I think it’ll make some aspects clear.

  4. Pingback: Gliese 581g: Earthlike Exoplanet may Harbor Potentially Rich Alien Life!! « WeirdSciences

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