Astrobiology

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==The Drake equation==
 
==The Drake equation==
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''See the main article: The [[Drake Equation]]''
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The Drake equation is a famous formulation that would allow one to calculate the number of advanced civilizations (defined as having invented radio) in our own Milky Way galaxy at a specific moment in time.  It was first presented in 1961 by astronomer Frank Drake.
 
The Drake equation is a famous formulation that would allow one to calculate the number of advanced civilizations (defined as having invented radio) in our own Milky Way galaxy at a specific moment in time.  It was first presented in 1961 by astronomer Frank Drake.
  
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Although the Drake equation does not include all possible variables, it is generally accepted as a helpful, though not authoritative, tool for the field of exobiology.
 
Although the Drake equation does not include all possible variables, it is generally accepted as a helpful, though not authoritative, tool for the field of exobiology.
 
Even when plugging in <ref>Adjust the Drake equation for Yourself <i>Astrobiology Magazine</i> [http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=512]</ref> very conservative estimates into the Drake equation the outcome postulates the existence of dozens of intelligent civilizations in our galaxy.
 
 
Indeed most scientists believe in the existence of (intelligent) life for statistical reasons, since our Milky Way galaxy is only one of the billions of galaxies in the universe.
 
 
One interesting thing to note is that factor "L", the time a civilization might spend indicating its presence, can be constantly updated by our one available observation.  The longer that mankind succeeds in not annihilating ourselves ''and'' continuing to broadcast, the longer we can guess other civilizations will do the same. 
 
 
Ironically, unless intentional signals are broadcast to outer space, we can also observe that "accidental" broadcasting might cease in favor of more efficient means of communications: cf. cable television replacing broadcast stations.<ref> Wikipedia has an [[wp:Drake equation|article]] on the Drake equation - of course.</ref>
 
  
 
==See also==
 
==See also==

Revision as of 15:22, 24 November 2008

Conservlogo late april.png
For those living in an alternate reality, Conservapedia has an "article" about Astrobiology

Exobiology is the science of extraterrestrial life. As such, it is largely theoretical, but still plays an important role in such arenas as the search for extraterrestrial intelligence (SETI) or ET life in general.

Exobiologists have to tread a fine line between assuming that some commonalities we observe in life on earth will be required elsewhere, and still working with the limitations that the chemistry and physics of the universe impose on possible biologies.

For instance, there is no reason to expect that life elsewhere would be based on DNA like ours, as that is probably a terrestrial adaptation that happened to work.

However, it is considered that temperatures and pressures leading to the presence of liquid water are of importance, due to water's role as an almost universal solvent or carrier of molecules.

When considering chemical-based life, it is also highly likely that carbon molecules will form a vital part of the picture, due to carbon's ability to form many kinds of molecular bonds, thus forming the basis of huge numbers of potential chemical processes.

When people involved in projects like SETI want to know "what to look for" in order to have a good idea of "where to look", they turn to exobiologists to try to improve their odds.

Contents

Life on rocky planets

Some exocritters can be photographed when they visit our planet.Do You Believe That?

Some rocky planets, such as Earth, are capable of supporting carbon-based "life as we know it". Conditions necessary for life are generally thought to be:

  • Orbit around a yellow star (like the Sun), a red dwarf, or a stable combination of those stars.
  • Presence of water, carbon and other organic elements (believed to be fairly common.)
  • Orbit within the habitable zone (distance from star where the temperatures allow water to exist as ice, liquid water and vapor).
  • Presence of an active core that causes volcanic and tectonic activity as well as a magnetic field to protect the surface from cosmic and solar radiation.
  • The size and density of the planet have to be such that the planet's gravity can hold an atmosphere, but is not too strong to crush lifeforms.

Out of all the known planets, Gliese 581c, Gliese 581d and Mars are the only planets (besides Earth) to meet these criteria even remotely, along with Europa, one of Jupiter's satellites, possibly other satellites of Jupiter, and perhaps even Titan, a satellite of Saturn. Allegedly, the majority of scientists at a conference hosted by the European Space Agency believe Mars has, or used to have, life.[1]

The habitable zone is an imaginary belt around a star, within this belt temperatures are such that liquid water, ice and vapor could all exist on a planet that describes an orbit through this belt.

In our solar system the inner edge of the belt lies between the orbits of Venus and Earth, while the outer edge extends roughly as far as the orbit of Mars. The habitable zone changes as the "solar activity" of the star system changes.

We must remember not to limit ourselves to searching for life on Earthlike planets inside habitable zones, as alternative scenarios have been proposed, such as volcanic activity providing heat on planets or moons outside of the habitable zone (similar to "smokers" on Earth's ocean floors), silicon-based life that can survive where carbon-based life cannot, and even floating, balloon-like lifeforms living in the atmospheres of gas giants.

Carbon-based life

All known life on Earth is carbon-based, since carbon is able to form long chains (in polymers as well as in living tissue). The reason for this is the structure of the carbon atom: carbon has 4 electrons on its outer shell and because carbon, like every other atom, tries[2] to attain the "noble gas" configuration (8 electrons on the outer shell, or 2 electrons if there is only one shell). Thus, carbon will bond with up to 4 other atoms.

Carbon is not the only atom with this structure: silicon is very similar to carbon and although it binds less readily than carbon, some bacteria are known to incorporate silicate structures in their physiology. Silicon-based life, however, is unlikely, as large silicate structures become unstable.[3]

The Drake equation

See the main article: The Drake Equation

The Drake equation is a famous formulation that would allow one to calculate the number of advanced civilizations (defined as having invented radio) in our own Milky Way galaxy at a specific moment in time. It was first presented in 1961 by astronomer Frank Drake.

It is usually written in the following form:

N = R* • fp • ne • fl • fi • fc • L

N = The number of civilizations in The Milky Way Galaxy whose electromagnetic emissions are detectable.

R* =The rate of formation of stars suitable for the development of intelligent life.

fp = The fraction of those stars with planetary systems.

ne = The number of planets, per solar system, with an environment suitable for life.

fl = The fraction of suitable planets on which life actually appears.

fi = The fraction of life bearing planets on which intelligent life emerges.

fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.

L = The length of time such civilizations release detectable signals into space.

Although the Drake equation does not include all possible variables, it is generally accepted as a helpful, though not authoritative, tool for the field of exobiology.

See also

External links

Footnotes

  1. http://en.wikipedia.org/wiki/Extraterrestrial_life#Direct_search
  2. This does not mean it "tries" in the sense that people make conscious efforts to attain goals. It means that in the state alluded to, (the absolute value of) the binding energy (the sum of the kinetic energy and potential energy) is lowest - the carbon atom is effectively "rolling downhill" when it forms bonds that fill these shells. Note that by convention potential energy and binding energy have negative signs.
  3. How large? And how "large" does life have to be?
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