Hello! Are we alone? If you're like me, you may want to know

[Pranab]

Alien life forms are generally regarded as the stuff of science fiction and fantasy and subject for/ from the movies by several times Oscar winnerHollywood director Steven Spielberg. But both SETI [While philosophers and biologists may debate the meaning of the term 'intelligence', for the purposes of the SETI project intelligence simply means the ability to build large radio telescopes and transmitter of high-powered radio signals or intense laser beams] and NASA's Exobiology Program, which seeks to understand the origin, evolution and distribution of life in the Universe, researchers are about to begin the SETI Microwave Observing Project. radio telescopes around the world which will search for signals produced by other intelligences. There are of course two schools of thoughts about intelligent life out there in the Galaxy, It is argued that life on the planet Earth, and especially intelligent life, is the result of an incredibly unlikely set of circumstances; and there is no intelligent life anywhere else in our Milky Way Galaxy, perhaps none in the entire Universe. But according to the opposing school argument, there are so many stars and planets in the Galaxy that, provided there is even a small chance of intelligence developing on any one planet it must have happened many times on many different planets. Nobody seems to take the middle view, that life is restricted to just a few planets in our Galaxy; either it exists solely on Earth, or there are many inhabited planets. If the SETI project detects just one signal, the implication will be that we are not alone, and that evolutionary biology is an inherent characteristic of certain locations in the Universe - planets like Earth.[1]

What are the requirements for development of life [simple, complex or intelligent] in universe especially in our galaxy Milky Way star’s planets? First of all, let us authors, to compose a list of possible astronomy related requirements for development of life on the planet Earth or if evolved in other worlds of our galaxy the Milky Way

2nd generation stars with heavy elements
* Large planetary family to absorb debris
* Iron core to generate magnetosphere
* Planet massive enough to retain its atmosphere
* Collision with planetoids to create voids in tectonic plates and large moon. [Please see LINK
(http://www.spacedaily.com/news/life-01x1.html)]
Spectral type stars: G, late F, early K, a late F or early K type star are also candidates for having life-bearing planets

Stable intensity of star
* Large moon to stabilize rotation because without large moon the rotational axis of the planet will be unstable
* Plate tectonic activity
* Water[ocean] by cometary’s seeding
* Recent nearby nova to clear out interstellar dust
please see LINK
(http://cse.ssl.berkeley.edu/chips_epo/science.html)
* Time between large impactors for life
* Main sequence star
please see LINK
http://homepage.sunrise.ch/homepage/schatzer/Alpha-Centauri.html)
* Adequate age for life to evolve
* Orbit within ' the habitable zone'
* Avoid close orbit and being tidally locked to star
* Not within a dense star cluster
* Sudden, occasional environmental/ecological changes to encourage evolution
* Planetary worlds whose mass is between 0.5 and 10 Earth masses (the current theoretical optimum size, gravity, etc for which life’s development is favorable due to the ability to hold atmospheres, plate tectonics, magnetic fields, etc.): Too little mass and the planet won’t be able to keep its atmosphere (and inevitably liquid water) for longer than a few billion years; too much mass and odds are fairly good that it’ll retain hydrogen and helium, thereby adding more mass to the planet that allows it to trap more H and He - thus starting a cycle that transforms the planet into a gas giant. (http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=436&mode=thread&order=0&thold=0)
*'Earth-like' conditions for life
Oxygen to nitrogen ratio in atmosphere. The oxygen to nitrogen ratio is determined by the presence of life and is, as such, self-regulated by life Oxygen to nitrogen ratio in atmosphere
1. If larger: advanced life functions would proceed too quickly.
2. If smaller: advanced life functions would proceed too slowly
3. Radioactive methane gas generated by volcanism or like nearly all methane in our own atmosphere is produced by bacteria and other life

Universe or our galaxy is possibly teaming with life according these authors particularly in the G & K class stars in the Galactic HZ. How many Planets may be there in that galactic habitable zone? We consider life itself is fairly common throughout this galaxy. How can we estimate the number of technological civilizations that might exist among the stars? While working as a radio astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, Dr. Frank Drake (now he is the Chairman of the Board of the SETI Institute) conceived an approach to bind the terms involved in estimating the number of technological civilizations that may exist in our galaxy. The Drake Equation, as it has become known, was first presented by Drake himself in 1961 and identifies specific factors thought to play a role in the development of such civilizations. Although there is no unique solution to this equation, it is a generally accepted tool used by the scientific community to examine these factors The equation is usually written:
N = R* x fp x ne x fl x fi x fc x L Where, 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. Drake himself estimates the final number of communicating civilisations in the galaxy to be about 10,000. As per Drake, we may calculate, for example- 0.333333333 7,300,613.497 planets may be containing any kind of life, intelligent or not. 0.333333333 973415.1329 "Jurassic" worlds or any other whose most intelligent species is sub-sentient. 0.333333333 12.16768916 planets whose most intelligent species is within (but not over) 5000 years of current Western World technological development i.e. ~ 12 worlds with 'planets whose most intelligent species is within [where life evolved without artificial intervention] . So planets with 'advanced technical civilizations are quite rare, if we consider civilizations not more than 5000 years old and If the average age of a civilization is a million years, that increases the number of intelligent species civilizations to 2400, In 2001, For the first time, the researchers estimated how many planets might lie in the "habitable zone" around stars, where water is liquid and photosynthesis possible. The results suggest that an inhabited Earth-like planet could be as little as a few hundred light years away. So it is obvious that within the limits of our existing technology, any practical search for distant intelligent life must necessarily be a search for some manifestation of a distant technology, The National Research Council of US has emphasized the relevance and importance of searching for evidence of the electromagnetic signature of distant civilizations.

Simple life or complex Life or Intelligent Life?
Simple life in some form microscopic may be more and more than complex life form or intelligent life form that understands physics or mathematics and target of SETI that may also does exist. Recent life forms have been also discovered that do not need solar energy to survive. Bacteria can live on energy derived from chemical reactions rather than photosynthesis. And, higher life forms survive by consuming the bacteria. So evolving to complex organisms is highly possible More complex life will certainly be rarer. If at all they exist we don't believe that we will ever make contact with them. Think once about the vastness of space and the age of the universe. The vast distance between stars and galaxies makes it less likely that any other life will be found because it takes to long to travel and combined with the increased rarity, it is extremely unlikely we could just go to the "next star over" and find complex life there. 2] Finally, with the age of the universe, other civilizations could have grown and dies out long before life even started to develop here. So what are the chances we could travel somewhere within a reasonable distance,
Which Stars in our Galaxy Milky Way?
Stars in our Galaxy Milky way- estimates: 500 Billion ( Royal Greenwich Observatory. And these stars include everything from M-Class (Red Dwarfs) to Enormous O- Class Stars (very hot, very fast burning, Blue stars). Our own star sun is Class G. Stars. K class stars are - The cooler and “redder” the star, the longer it remains on the main sequence (barring the obvious exception of red giants). The previously-mentioned O-Class (very hot blue) stars will likely last only a few dozen million years, barely enough time for star dust to coalesce into planets. Furthermore, hotter stars emit enormous quantities of ionizing radiation (UV or higher). In fact, large stars tend to emit the bulk of their radiation in the UV band. Stars in classes B (a lower level blue-white) and A (white) suffer similarly, though to not to the extreme extent as O-class ones. Nevertheless, these stars will last only a few billion years at most. This may be long enough for simple life and perhaps even the simplest animal life to form, but not likely enough to allow technologically advanced life to arise (unless its evolution is incredibly quick). F-class (white) is likely to last from 4 to 6 billion years, certainly enough to give rise to complex life (perhaps even intelligent life). Unfortunately, in the Earth-term timeline at least, a white sun will start to leave the main sequence just when intelligence does arise. Timing truly is everything. So while it’s certainly possible and even plausible for a white sun to have a technically advanced civilization, I don’t find it particularly likely.
By contrast, the red dwarf (M-class) stars will be around for billions of years, much more than enough time for life to form. Furthermore, they do not emit as much ionizing radiation as even our own sun (G-Class), another factor favoring a life-friendly environment. Unfortunately, the cooler the star, the narrower its life zone. I personally interpret this fact to mean that a red star’s HZ will be less likely to contain a planet of any sort, let alone one with other preconditions necessary for life to have a chance on it. Even if the red sun’s HZ does have a planet with the appropriate gravity, atmospheric and other characteristics, odds are fairly high that the planet will suffer from “rotation lock” (one face always facing the star). This means one side will be in eternal day or close to it (thus rendering it too hot) and one side will be in eternal night (rendering it too cold). However, there is still at least some chance other mitigating factors will come to play on such a planet (the hot spot over the planet may create atmospheric convection that creates winds, thus spreading heat more evenly over the planet). Obviously, a rotationally-locked planet’s twilight zone could offer a happy medium in which life, and even intelligence can flourish in theory. However, as I will discuss later, such a planet will have a much more difficult time developing a sustainable high technology civilization, and even a high-end pre-industrial civilization. G (yellow), K (orange), and low-level white stars as places favorable for advanced civilization to arise. If we include all G and K stars, plus about 1/3 of all F stars, these stars are about 22% of all stars in the galaxy ( Wikipedia). If M-class (red) stars - 78% of all stars - permit HZ planets without a rotation lock, then perhaps another 10 % of all stars (the hotter M-class ones) can be added to (though I admit this number is rather arbitrary). So we can say that as many as 33% of all stars could support a technical civilization, given other necessary planetary conditions listed above. Such stars that are the appropriate age - If you are content with finding significant life in any form, you will likely find it around planets between two and five billion years old. This is certainly long enough for life to form an Oxygen atmosphere (strong evidence of life), though not necessarily sentient life. Hopefully, by 2016-2020 the Terrestrial Planet Finder (TPF) project will finally give the answers we all want--where there are rocky crust planets orbiting around G to K class stars within 200-300 light years of Earth. The TPF mission will survey number of Earth-sized planets in habitable zone orbits in the galaxy
Any special Signal received yet by SETI? In August 1977, an Ohio State University radio telescope detected an unusual pulse of radiation from somewhere near the constellation Sagittarius. The nearest star in that direction is 220 million light years away. The 37-second-long signal was so startling that an astronomer monitoring the data scrawled "Wow!" on the telescope's printout. The signal was within the band of radio frequencies where transmissions are internationally banned on Earth[3] In February 2003, astronomers with the search for extraterrestrial intelligence (SETI) project, used a massive telescope in Puerto Rico to re-examine 200 sections of the sky which had all previously yielded unexplained radio signals. These signals had all disappeared, except for one which had become stronger. came from a spot between the constellations Pisces and Aries. SETI has many signal detectors type. Recently in 2008 SETI signal detector called SonATA (SETI on the ATA). Son ATA does everything that Prelude does, but it is a software-only detector, capable of operating on commodity servers, without the special-purpose hardware accelerators that had to be built into Prelude to make it run in near-real time .On October 9, 2008 the X-band signal from the Rosetta spacecraft was detected by the SonATA as a demo system! Figure 1 shows that detection. The Rosetta X-band signal is much stronger than the signals from [4]Voyager fig1- Figure-. After a half-century of scanning the skies,SETI astronomers today have little to report. Why?. The problem could be that SETI had been so long looking in the wrong place, at the wrong time, and in the wrong way. "Why to waste time looking for old-style radio signals? The advanced and intelligent aliens may use entangled particles like neutrinos or some form of gravity waves to signal us Figure-1

How the Aliens Will Look Like in other Star’s worlds?


Let us to assume that our own humanoid form is the generic result of an ideal set of criteria by the creator which hold true universally? Perhaps all biologic life strives for carbon-based, oxygen-burning chemistry, and to see the planet by the visible light spectrum. There's no reason these laws should be very much different on other planets of other stars, if the universe is composed of the same small number of elements, which seems to be the case. So the aliens will probably have a close/ similar appearance to humans or animals in the earth, if they are found to be living in an environment and climate similar to ours but may appear as monster based on gravity of that planet. Aliens may have the same DNA as we do here on Earth. There are several types of nucleic acid that might be useful for genetic storage and transfer of information; tRNA, mRNA, aDNA, zDNA, even PNA. Three and four stranded varieties sometimes occur.
It is possible that the variety which life on Earth utilizes may predominate on many planets; it might be the most suitable type for living creatures and will be selected by evolution on a biochemical level. Even if this is true (and I don't think we can be sure yet) there are two mirror-image forms of DNA which are possible; we never encounter the mirror image L-DNA in nature as far as I know(as opposed to zDNA, which is completely different in form) but it could occur on other worlds.
We think that many alien intelligent species (perhaps 2 or 3 percent of them) would look like humanoid as they look, act, think and feel amazingly like ourselves with probable some kind of appendages evolved for manipulation, locomotion. These appendages can have evolved from any movable body parts, including parts of the locomotors apparatus (limbs), feeding apparatus (mouth parts like lips or mandibles), respiratory apparatus (gills), or sensory apparatus (antennae).s Earthlike worlds with slightly more gravity would tend to produce centauroids. The nearest centauroid might look like the upper part of a gorilla transplanted on the body of a donkey, for example. And its two eyes might be above each other, rather than side by side. Earthlike worlds with slightly less gravity would tend to produce flying aliens. Some might look like bats, others like octopoi with a balloon-like body, yet others like living monoplanes, with their manipulative extremities tucked away inside their mouths. In a dense atmosphere a life form might look like a living umbrella, which keeps a loft by opening and closing itself. Earthlike worlds with vast tracts of level ground might have inhabitants which look like giant wheels. The outside of the wheel might be covered with tiny mouths used for grazing. Ant like creatures and some reptile like, some are giant larger than elephant also, may be possible, and some like octopus also, aliens are aliens even we are aliens for them.
Possibility of life in other planets of our own solar system?
There may be no little green men living in our Solar System. However, there are plenty of places where more primitive life might be able to survive. Many astronomers now believe that life has a good chance of evolving wherever the conditions are right. So our Solar System could be teeming with living creatures The main candidates in the Solar System to harbor life are Mars, Europa and Titan. Europa is an icy moon that revolves around Jupiter The temperature on the surface is a chilly -170ºCBut this inhospitable planet may harbor an underground ocean of liquid water - one of the essential ingredients for life.
References
1] JOHN GRIBBIN Is anyone out there?: NASA researchers have started to search the Galaxy for signs of intelligent life. What sort of life do they hope to find? New Scientist 25 May 1991 Magazine issue 1770
2]http://www.badastronomy.com/phpBB/viewtopic.php?t=4570&sid=46ce3673996d676dc0bdae2e16d1c931 by Rafael Austin
3] John Pickrell Top 10: Controversial pieces of evidence for extraterrestrial life New Scientist11:30 04 September 2006 A mysterious radio signal is received by the SETI project on three occasions - from the same region of space and1977, The unexplained extraterrestrial "Wow!" signal is detected by an Ohio State University radio telescope

Authors_:
**Professor Pranab kumar Bhattacharya- MD(cal) FIC Path(Ind), Professor of Pathology, Institute of Post Graduate Medical Education & Research,244 a AJC Bose Road, Kolkata-20, West Bengal, India** Mr. Rupak Bhattacharya-Bsc(cal), Msc(JU), 7/51 Purbapalli, Sodepur, Dist 24 Parganas(north) Kol-110,West Bengal, India ***Mr.Ritwik Bhattacharya B.com(cal)7/51 Purbapalli, Sodepur, Dist 24 parganas(north) ,Kolkata-110,WestBengal, India****Miss Upasana Bhattacharya- Student, Mahamayatala, Garia, kol-86,daughter of Prof.PK Bhattacharya**** Mrs. Dalia Mukherjee BA(hons) Cal, Swamiji Road, South Habra, 24 Parganas(north) West Bengal, India**** Miss Aindrila Mukherjee-Student ,Swamiji Road, South Habra, 24 Parganas(north), West Bengal, India****; Mrs. Chandrani Dutta Bsc(zoology) ****Dr Avisnata Das MBBS (cal) Pathology, Institute of Post Graduate Medical Education & Research,244 a AJC Bose Road, Kolkata-20, West Bengal, India, Dr. Tarun Biswas MBBS(cal) Demonstrator,Pathology, IPGME&R, Kolkata-20, Dr. Hriday Ranjan Das MD(cal), DTM&H(cal), Dept of Nephrology, IPGME&R, 244a AJC Bose Road


Acknowledgement- To Recently Diseased Late Mr. Bholanath Bhattacharya and Late Mrs Bani Bhattacharya- Diseased parents of Professor Pranab kumar Bhattacharya of 7/51 Purbapalli, Po-Sodepur, 24 Parganas(north), Kolkata-110, West Bengal-India, who belived presence of life in other forms in other worlds in Galaxies and panspermia theory

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