Alien Life May Exist
It seems that we must be prepared to find life where we don't expect it and in forms we have never seen before and this could even be the case within our own solar system!
An article in yesterday's Space.com says a group of scientists, who published a paper in the journal Life, believe that we may be too “Earth-centric” in our search for life and we may be limiting ourselves in our concept of what life is and how it can develop.
Most exploration of the cosmos has so far centred on finding planets with the same environment as our own. It is possible we will find extraterrestrial life that needs neither oxygen, water or sunlight to survive. Even on our own planet, we have discovered bizarre life forms living in conditions which defy our standard definitions of nature.
An article in Live Science gives some examples of extreme life forms or "extremophiles" here on Earth which contradict existing biological theories. We know, for instance, that some bacteria can live inside rocks and certain microbes can withstand severe levels of radiation and temperature.
The Aquifex bacteria, for example, lives in hot springs in Yellowstone National Park at temperatures of more 205F or 90C. Then, there are thermococcus microbes living in the thermal vents of underwater volcanoes at super high temperatures and using so little energy to survive through chemical reactions thought impossible. At the other extreme, there are psychrophiles, which can exist in super low temperatures in ice, glaciers and deep oceans.
Even more strange are deinococcus radiodurans bacterium which are immune to 15,000 gray doses of radiation, while 10 grays would kill a human. Endoliths live so deep underground that there is virtually no water and scientists believe they may survive by living on iron, potassium and sulphur, while newly discovered loriciferans survive without oxygen at all!
The group of scientists who are suggesting the existence of such life in outer space say that creatures could exist without water and still evolve and survive on CO2 alone or what they call "supercritical" carbon dioxide, which has the properties of both a liquid and a gas. While CO2 chemical reactions aren't considered capable of creating conditions for life as we know it, supercritical CO2 could create more stable conditions for enzymes than water does.
Scientists have studied supercritical CO2 in the lab and have now found that certain bacteria are tolerant of it and some microbes are present within it. Supercritical CO2 is known to exist in our oceans, but at depths which are impossible to explore.
The researches believe other worlds may be based on supercritical CO2 and exotic forms of life could exist there. Indeed, they even hypothesize that this might be the case on nearby Venus, which in earlier period in its existence had conditions similar to Earth and it is possible that remnants of this life have survived on in the current CO2 environment.
Air&Space magazine explains,
“Carbon dioxide is usually not considered a suitable solvent for life, at least not on Earth. But its chemical and physical properties change quite dramatically when it becomes supercritical. Above its critical point, CO2 mixes well with a variety of organic compounds. It participates in a number of organic synthesis reactions, and some bacteria and their enzymes have been shown to be active with supercritical CO2 as a solvent.”
An article in Wired.com quotes physicist Abel Mendez of the University of Puerto Rico, home to the giant Arecibo telescope used to scour the Universe for signs of life. “We are trying not to be geocentric, calculating planetary habitability independent of liquid water,” he said.
Abel Mendez's team is proposing to rank planets by two scales rather than one. It suggests that a new a broader Planetary Habitability Index (PHI) should be added to the current Earth Similarity Index (ESI) which is being used now, Wired.com explains.
“The first index looks at how close a planet is to Earth in mass, temperature, and composition while the second is based on the whether or not it possesses more exotic chemistries, liquids, and energy sources than found on our planet. Alien life could be based on elements other than carbon, require liquids other than water, and gain energy through means other than sunlight.”
Within our own solar system, for instance, Saturn’s moon Titan is a tiny world where water is only available in frozen chunks hard as rock. But its temperature range makes possible the existence of lakes and rivers of liquid hydrocarbons, leading some researchers to speculate that native life could exist there.”
Scientist have discovered more than 700 planets outside our solar system, most of which have been written off as candidates for life because of their orbits or gas-based character. However the current research would now include them as possible habitats for exotic life forms completely unrelated to us.