*Professor Pranab kumar Bhattacharya-MD(cal) FIC Path(Ind), Professor & Head of Department of Pathology, convener In charge DCP and DLTcourse WBUHS Calcutta school of Tropical Medicine;108 C.R Avenue Kolkata-73;West Bengal, India Ex Professor and HOD ophthalmic pathology, RIO, Kolkata, Ex Professor IPGME&R Kol-20 WB And of WBUHS, * Miss Upasana Bhattacharya- Student, Mahamya appartment Mahamayatala, Garia, kol-86, only daughter of Prof. PK Bhattacharya ** Mr.Rupak Bhattacharya-Bsc(cal), Msc(JU), **Mr.Ritwik Bhattacharya B.com(cal),** Miss Rupsa Bhattacharya , **Mr. Soumyak Bhattacharya BHM, MSC Student PUSHA New Delhi **all of residence 7/51 Purbapalli, Sodepur, Dist 24 Parganas(north) ,Kolkata-110,WestBengal, India *** Mrs. Dalia Mukherjee BA (hons) Cal, ***Miss Oaindrila Mukherjee- Student, Mr Debasis Mukherjee BSC(cal) ***all of residence Swamiji Road, South Habra, 24 Parganas(north), West Bengal, India,
* 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
* 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
* Time between large impactors for life
* Main sequence star
* 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
1. If larger: advanced life functions would proceed too quickly.
2. If smaller: advanced life functions would proceed too slowly
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
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.