What Life and Planets need to co-exist

The Earth seen from Apollo 17.

The Earth seen from Apollo 17. (Photo credit: Wikipedia)

 So what is it that makes a world such as Earth capable of hosting life? Scientists often agree that there are a few key ingredients needed for life to exist, but what limits there actually might be on types of life-forms is hotly debated, our own planet hosting some very unusual creatures living in very extreme environments indeed.

The first, and most important ingredient for life would have to be some kind of liquid, where molecules can go to react with one another. In any such soup, the ingredients making up life as humanity knows it – DNA, proteins etc. – can interact with one other to get reactions needed for life underway. This liquid, it is commonly believed, is water, because of the ability it has to exist in three states at once.

The second consideration is the location of the planet concerned, and astronomers these days, when seeking out extraterrestrial life, tend to focus most on planets in so-called habitable zones of stars. These are orbits neither too hot nor too cold for liquid water to persist on planet surfaces, just as Earth sits in the so-called Goldilocks mark of our own sun.

Other scientists, though, such as astro-biologists, are sure that these views are too narrow, and that humans need to look beyond conventional habitable zones, especially in light of the proven existence of so-called extremo-phile organisms here on Earth. Also, any life-form will require energy.

For copyrights, see Image:Gliese.JPG (the orig...

For copyrights, see Image:Gliese.JPG (the original image that this image was derived from) The copyright tag found in Image:Gliese.JPG is the following: The original author was Hervé Piraud (Photo credit: Wikipedia)

On Earth, it is sunlight which drives the entire life cycle, so the feeling is that, throughout the cosmos, there will likely be no shortage of energy sources for life to exploit and thrive, though of course – again using earth as the example – any habitable worlds would need to orbit stars existing for at least several billion years, so that evolution can do its work, though of course, as yet unknown life  might originate much faster than on our planet.

Earth is some 4.6 billion years old, and the earliest known organism first appeared some 3.5 billion years ago, so that complex life may take a billion years to, so relatively long-lived stars have a part to play. Another factor might be, as with our own sun,  little variation in radiation output, alongside a planet possessing a protective magnetic field.   

To date, our own Earth still remains the only known planet to be capable of hosting life, because a unique combination of factors exist here that encouraged it to flourish, but as ever more exo-planets are discovered, our continuous monitoring of such alien worlds might,  one day in the not so distant future, find either other planets that share these Earth attributes, or alternatively unearth other ways that life has found in which to thrive in other areas of the vast cosmos that surrounds us. 

 

Size comparison of terrestrial planets (left t...

Size comparison of terrestrial planets (left to right): Mercury, Venus, Earth, and Mars (Photo credit: Wikipedia)

Size comparison of terrestrial planets (left to right): Mercury, Venus, Earth, and Mars (Photo credit: Wikipedia)

 

 


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