Journal of Aerospace Engineering & Technology (JoAET)
(2019-59 © STM Journals 2019. All Rights Reserved Page 30 -39Journal of Aerospace Engineering & Technology ISSN: 2231-038X (Online), ISSN: 2348-7887 (Print) Volume 9, Issue 1
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Super-earths (Exo-planets): How Much Probability ofColonization of Life is There?
Rupak Bhattacharya1, Pranab Kumar Bhattacharya2,*, Upasana Bhattacharya3,Ritwik Bhattacharya4, Rupsa Bhattacharya5, Dalia Mukherjee6, Ayshi Mukherjee7,Debasis Mukherjee8
1B.Sc (Calcutta University), M.Sc (Jadavpur University), Kolkata 110, West Bengal, India 2MBBS (Calcutta University), MD (Calcutta University), FIC Path (India), Now Professor of Pathology (on Deputation) , Calcutta School of Tropical Medicine, Kolkata, West Bengal, India; also, Professor in Department of Pathology at Murshidabad District Medical College, Berhampore station Road, Murshidabad, West Bengal, India 3Student, Kolkata-110, WestBengal, India 4B.com, Calcutta University, Kolkata, West Bengal, India 5Student, Kolkata-110, WestBengal, India 6B.A. (Hons.), (Calcutta University), Kolkata, West Bengal, India 7Student, Kolkata, West Bengal, India 8BSc (Calcutta University), West Bengal, India
Abstract
On January 4th, 2009 American Astronomical Society in Washington D.C, the Kepler team announced that it had identified first new exo-planet and after that up to 2013, Kepler had identified nearly 4034 exoplanets or Super earth outside our solar system where some chemical conditions that the pre-biotic earth had might have prompted life, at least in form of microbes. Scientists so far announced the lists of earth-sized 4034 exo-planets with a duration of orbit around their stars from 6 hours to 632 days and from the list, Kepler team singled up to 20 candidates most likely to have characteristics necessary to sustain life. Of such planets are HD 1461 (76 light years away); GJ 1214b(40 light years away), GJ 452 b ( Which is one and half time sized in the earth and is around 40 light years away); Gliese 581 c and another is KOI -7923.01. This last Exoplanet is 97% of the size of our earth has an orbit period of 395 days of our earth days, likely surrounded by a cold atmosphere. Super-earth Wolf -1061 C is however habitable planet outside our solar system and could support also alien life. It is only 14 light years away from the earth. Statistics suggest that our own galaxy harbors at least 100 billion such exoplanets including planetesimals. Of the world’s found, today few closely resembles the earth. Instead, they exhibit truly enormous diversity, varying immensely in the orbit, their size, composition and circling a wide variety of stars including one significantly smaller than our sun. Diverse features of those exo-planets suggested us (the authors) and also to many others that earth may not be only where close to the pinnacle of habitability. In fact, some exo-planets are quite different from our own, could have much higher chances and can maintain stable biosphere. Of course our planet the earth possesses a number of properties at first seems to be ideal for evolving life, that earth revolves around a sedate middle-aged star, that has shined steadily for billions of years, giving life plenty of times to arose and evolved from RNA worlds to microbe worlds to prokaryotic to eukaryotics to multicellular organism life to modern planets, reptiles mammals, human through a process called Darwinian evolution. It has oceans of life-giving water, largely because it orbits within suns habitable zone, life-friendly size, big enough to hold a substantial atmosphere with its gravitational field but small enough to ensure gravity does not pull a smothering, opaque shroud of gas over the planet earth size its rocky composition, its volcanoes also gave rise to other boosters of habitability of life Wolf 1061 C is the closest Super-earth from our planet, only 14 light years away. But it has more than 4 times the mass of earth and the planet sits within the habitable zone, possible for water and life to exist. Others are in the habitable zone of cool dwarf star known as TRAPPIST -1 which is 39 light years away from earth and the planets have a surface temperature from zero to 100 degree Celsius - the temperature, which is perfect for supporting life. Earth-sized planets those are rocky, those are watery, NH3 has methane, and volcanoes can support the origin of life. The amonia methane, HCN and water are an essential components for the origin of life in any planet Super-earths (Exo-planets) Bhattacharya et al JoAET (2019) 30-39 © STM Journals 2019. All Rights Reserved Page 31 for RNA and DNA. To develop most earliest microbes it need methane-rich oxygen-poor mud at bottoms of river and lakes as microbes live on a diet of methane and nitrogen oxides like nitrites and nitrates or by other pathways like photosynthesis, bacterial reduction of chlorates and enzymatic conversion of reactive oxygen species and directly energy from methane through a chemical process linked denitrification which releases nitrogen and oxygen from nitrogen oxides. So life can begin in any of twenty super-earths where methane exists as free gas in the atmosphere or in the river or as a lake or asthe ocean. In such an environment, alien microbes can use any of the pathways to leave off carbon and energy supplied by methane. The bacteria may be called methanotrophs.
Keywords: Gliese 581 c, glycine RNA/DNA life, habitable zone, HCN, HD 1461, KOI -7923.01, methane, methanotrophs, Miller Urey experiment, super earh, TRAPPIST-1volcanos, water, Wolf 1061 C*
Author for Correspondence
E-mail: profpkb@yahoo.co.in
INTRODUCTION
Are "Super-Earths" common around other star systems also in our universe? Are these planets at all habitable, particularly suitable for human colonization? Quite possibly there are many Super Earths. Astronomers also found a handful of new planets around sun-like stars beyond our sun and our galaxy [a total of known such extrasolar planets today is probably more than 4000.], some may be only 39 light years away, some are 14 light years away. Astronomers have discovered hundreds of Jupiter-like planets in our galaxy too. In a study published in Nature journal, by a team, led by David Charbonneau of HarvardSmithsonian Center for Astrophysics, reported [1] a new Super-Earth - hot, watery, and only 2.68 times the size of our own world the Earth. The planet currently bears the name GJ 1214b, which orbits a red dwarf star (Figure 1), approximately 40 light-years from our Earth, and probably is not habitable because of its 400-degree Fahrenheit surface temperature. But the new planet are most likely holds a lot of water even in ocean form and its density is one-third that of our Earth. The planet radius is 2.68 times that s of Earth’s radius (R), and is about 6.55M times as massive as earth. It is the second smallest planet discovered outside of our solar system to date, trailing behind only CoRoT-7b, which is 1.7 times Earth's size and about five times as massive. Charbonneau's team thinks GJ 1214b is likely a water world with a solid center. Moreover, the planet has a thick surrounding atmosphere of hydrogen and helium. But scientists think the thick atmosphere of GJ1214b creates a high-pressure environment that keeps water on the surface in a liquid state.That's just speculation, however, If life exists there, it would probably be well adapted to swim in 400-degree oceans (and actually it may be cooler than, depending on the planet’s albedo]. Figure 2 shows Kepler pin down planet size tuning to the music of the sphere.
Fig. 1: GJ1214b Orbiting a Red Dwarf Star.
Fig. 2: Kepler Pin Down Planet Size Tuning tothe Music of the Sphere. Courtesy: NASA/JPL.
Journal of Aerospace Engineering & TechnologyVolume 9, Issue 1ISSN: 2231-038X (Online), ISSN: 2348-7887 (Print)JoAET (2019) 30-39 © STM Journals 2019. All Rights Reserved Page 32
WHAT ARE SUPER EARTHS?
Super-earth had been found in our nearby stars also. Six such "super-Earths" had been found orbiting our sun-like neighbor stars in our galaxy. The smallest of the bunch weighs in at about five times the mass of Earth and orbits a star known as 61 Virginis, which is visible with the naked eye in the constellation Virgo. The star is 28 light-years from Earth and closely resembles the sun in size, age and other attributes. Two other newly detected planets -- each about the size of Neptune -- are part of 61 Virginis' family. Another planet that is 7.8 times larger than Earth orbits HD 1461, a sun-like star located 76 light-years away in the constellation Cetus. Super-earths are thus very common all over the universe. In general, Super-earths are defined exclusively by their mass, and the term does not imply temperatures, compositions, orbital properties, or environments similar to earth. A variety of specific mass values are cited in definitions of Super-earths. Super-earths are planets- so named however for their size, - which ranges from about 2 to 10 times that of earth masses - may be superior to the earth, when it comes to the questions of sustaining life. Super-earths have terrestrial surfaces or liquid oceans that however can support life as we know it. Astrobiologists thinks, we are more likely to find a life on rocky planets with liquid water, though not an single super earth has been detected so far with life or ocean like earth planet.They estimated that there could be a hundred million such habitable Super-earth planets just in our Milky Way galaxy. They predict that we’ll find more 50 to 100 Superearth planets in the next 5-10 years. The Super-earth are traced by the detection of the stellar light reflected by that planet or of the thermal photons emitted by the planet. Both approaches are however valid and may provide complementary information. The planetary properties those are observed and scientists are interested in observing and constraining are: the size (mass and radius), the atmosphere (chemical composition, clouds, seasonal variations, and thermal inertia), and the surface (type -rocks, ice, water, “vegetation”-, in homogeneities), rotation (period, atmospheric dynamics) and environment (rings). Reflected light and/or thermal emission may be used to study these planetary characteristics. The former approach relies on the information that can be extracted from the stellar light reflected by the planet as a function. The NASA started The Super-Earth Explorer Corona graphic Off Axis Space Telescope (SEE-COAST) mission in 2016.
ARE SUPER EARTH SUSTAINABLEFOR LIFE
But are these super earths will be habitable for the life or sustaining for life? More the massive a planet is the hotter is its interior. Tectonics is one of the key features of our planet which however made once life possible here. If not for tectonics, carbon was highly needed by life would stay locked within rocks. Our life is carbon-based RNA/DNA life. Super-Earths, with a larger and hotter interior, would have a thinner planetary crust placed under more stress. This probably would result in faster tectonics, as well as more earthquakes, volcanism, and other geologic upheavals. Earth has a circular orbit 150 million kilometers away from the Sun, a yellow dwarf star. This helps keep conditions warm enough so that our oceans don’t freeze over, but cool enough so that we don’t lose all our water through evaporation. Let us consider how life evolved in the planet the earth [2].
HOW LIFE EVOLVE IN OURPLANET THE EARTH?
The Evolution of Planet & Planetesimals The Earth was considered to develop out of interstellar gas and dusts somewhat 4.6 billion years ago and from the fossil records, we know that origin of life happened soon after 4.0billion years ago that was either in the ocean or in ponds or in the rocks of the primitive earth. At about 4.5 billion years ago (Ga) a portion of interstellar cloud attained a critical density after which it underwent collapse phenomenon to form the Star “Nebula”. This Solar Nebula was a rotating disk with a central bulge. Half or more of the mass of that solar nebula was concentrated into a solar mass, and this central mass subsequently evolved to our Sun. In the extended disk, outside the central condensation, a portion of a tiny fraction of the nebular mass, that was in the form of solid grains settled out of nebular gas to form a dust-rich layer in the central plane of that disk. Super-earths (Exo-planets)
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In the inner portion of the disk, which was a much warmer portion of the disk, the dust consisted of grains of nickel, iron and silicate metals. In the outer portion, which wasa cooler portion of the disk, abundant grains of ice and organic compound accumulated along with augmented layers of solid matter. The solid matter within these dense, dirty layers, grains, water, ice, agglomerated to form clumps. The clumps continued to accrete until much of the solid matter was tied up in kilometer-sized planetesimals. Gravitational forces became important at this scale and larger bodies of hundred to thousands kilometer size or more were formed further by the accumulation of these formed up planetesimals. At some points of this process, a few of these bodies began to grow very rapidly at expenses of their smaller neighbors and formed embryonic planets. The nebula from which such embryonic planets were formed had the same composition to the sun, mostly hydrogen, and helium and a small sprinkling amount of heavier elements, Oxides, and hydrides of heavier elements, that must have condensed into particles and accreted to form final planets. The Jovian planets then were able to retain a substantial amount of gas as well. Their satellite and their ring system [like that of Jupiter, sat tern] also contained ice, water and rocks [oxides and hydrides of heavier elements]. The terrestrial elements were mainly rocks and a small amount of icy material. This icy material appeared on the atmosphere of earth planet or on the other planets also but much on earth planet and later helped to form the ocean. The original dust grains then accreted by a process, which is still not very well understood into bigger and bigger objects. It is assumed that there were about 500 of these planetesimals roughly of the size of the moon. The Thermal Escape Theory The merging of these planetesimals gave birth to planets in the region, now occupied by terrestrial planets. So the planets found although different in each run must have a general resemblance to what we find in the solar system. After the planets were formed each planet was too hot. Then there occurred “thermal escape”. Thermal escape process is the classical example of light gas also. It is then known as “Jeans escape”. The basic idea of jeans escape was that above some critical level, we call it “Exobase’ atoms were in highvelocity tail of Max William distribution and must escape, if they were directed upward at or above the escape velocity, was for earth 11.2 Km/second. The exobase level for the earth was500-600 kilometer. Thermal escape phenomenon explains explain to us that the most massive bodies of the solar system had a dense and denser atmosphere. Thermal escape also says that atmosphere was the generally deficient atmosphere in light atoms such as hydrogen and helium. Thermal escape also suggests that heavy gases, even nitrogen (N) must be stable for planet earth and planetesimal moon. But Thermal escape Phenomenon theory, later on, found unattractive before the scientist because of the following reasons that The Blow of Evolution Theory 1) The escape was from a level with low density 11) The principal term in the Jean escape equations was e –GMm/KTr where G was the Newton’s gravitational constant M,r,t was M= Planetary mass, r= radius=Temperature exobase,m=atomic mass, K= Boltzmann's constant. So after thermal escape theory came ‘Blow off evolution theory”. According to this theory, a rapid hydrodynamic outflow of light gas can carry along with it heavier gases at a rate that has a liner dependence on mass rather than the exponential on of Jean's mass Equation. Likely gases were H, Hydrogen, or possibly CH4. The mechanism for loss of heavier atoms was essentially an aerodynamic drag. Because all gas atoms had at that time nearly the same diameter and they’ll experience an upward drag. But at the same time, these gases also experienced a downward drag due to Gravity. And the net vector force was strongly mass dependent. Indeed for the heavier atoms, the drag force could be smaller than weight. According to this theory, H must come from accreted gas or from water vapor on planet earth, which could be photodissociated or react with hydrocarbons or with crustal iron. The solar heat than to run this flow were ionizing one and less then~100nm which contained ~ 1x10-5 of present solar spectral power. So to drive a suitable flow of Hydrogen from earth
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would require ~100 times as much as short wavelength radiation decay over a period of few hundred million years. G. W. Wetherill [3] suggested that earth formed 10010 million years and earth’s interior was initially very hot as a result of large asteroids or commentary or planetesimals impact events Watherill [3] suggested that earth’s core was probably formed simultaneously with accretion As a result iron, nickel was removed from earth’s upper mantle. Volcanoes As early as 4.5 billion years ago (Ga) volcanic gases started to release and had been relatively oxidized. Moreover, many of earth’s volatile gases were probably released on impact. This process might have formed a steam atmosphere during at least in a part of the accreatory period. Simultaneously the escape phenomenon went on with H and H2 Rapid hydrodynamic escape of hydrogen could drag the other gases with it particularly lighter isotopes, which were carried off more easily than heavier one. Hydrodynamic escape, however,, became difficult after 4.5 Ga in post accretion era, because after ~4.5 Ga the solar ultraviolet flux was lower and energy available to fuel up the escape process phenomenon were greatly reduced. Further more the escape rate became limited by diffusion once hydrogen became a minor component of the accreatory atmosphere, as a consequence of the reduction of water by infalling metallic iron-rich planetesimals or asteroids as impacts. The water or ice vaporized due to the heat generated by in fall of impact on earth’s surface as huge bombardments from space. Rainy Atmosphere Then Started the Rainy Atmosphere Once the main accreatory phase had ended, the surface heat flux of the earth had come down much and the steam atmosphere was rained out for 0.3 Ga with heavy lightening on the sky of Earth. Ocean was thus formed on the earth’s surface. The remaining atmosphere would probably then dominated by carbon and nitrogen compounds, mainly in the form of CO2, CO, N2, NO. Next to water carbon atom was most abundant in the volatile form in earth’s atmosphere & in the surface. Most of the carbon atom was in relatively nonvolatile form in the carbonate rock, under the ocean. The estimated crustal abundance of carbon was~1023, which was sufficient to produce 60-80 bars, where all of it present in the atmosphere of earth as CO2. Moreover as much as 15% of this carbon resided in the atmosphere before continents of earth started to grow in the ocean and carbonates rocks began to accumulate on the earth surface. This type of atmosphere was for the first several hundred million years. The mean surface temperature of the earth was then ~850 °C. Even after the main accretion period ended the earth surface environment underwent further rapid changes. Comets Impact Significant numbers of large impactors [>100Km in diameter] continued to hit both the earth’s and moon surface, until at least 3.8 billion years ago (3.8Ga). Some of these imp actors were of commentary of carbonaceous chondrite composition and quiet substantial amount of water and Ice were brought on earth surface for a period Of 0.7 billion years through these commentary bombardments, as if comets were used as a vehicle for organic compounds as well water for the earth, from space. These impacts also did effect the earth’s atmosphere composition by providing a source of CO&NO. CO could have been also produced by oxidation of organic carbon in carbonaceous impacts or by reduction of ambient atmospheric CO2 by iron-rich impactors. NO would have been also generated by shock heating atmospheric CO2 &N2. The heavy bombardments of impacts on the earth’s surface at about 3.8Ga. 3.5 Ga as evidenced by the presence of micro fossils and stromatolites probably started life in the ancient samples [4]. The narrow window of time between 3.8Ga and3.5 Ga was the most probable time for the life to be originated on earth’s surface. Before 3.8Ga the uppermost layer of the ocean on the earth’s surface would probably have been evaporated several times & repeatedly by the large impacts. Impacts however larger than 440 Kilometer in diameter could have vaporized water from the entire ocean in earth sterilizing the planet with possible exception living in sediments and submarine hydrothermal region for some hundred years. Events of these magnitudes Super-earths (Exo-planets)
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were possible before 3.8 and probably before 4.5 Ga.
EARTH’S ATMOSPHERE HISTORY & MILLAR UREY EXPERIMENT
Thus the probability of life could have originated many times during the first part of earth’s atmospheric history but if though originated it did not survive until towards the end of heavy bombardments of impacts. The reader of this article will like to Know what was the atmosphere consisted around 3.8Gaon earth? Because the atmosphere played a major role as per the Miller Urey jar experiment [5]. Both of them were awarded Nobel prize for their Experiments and conclusion. Miller Urey experiment showed that many biologically important macromolecule, important organic compound including sugars and amino acid (Glycine) could be formed by a spark discharge simulating Lightening {During impact bombardment period and steamy weather to rain fall on earth surface & further vaporization of upper layer of ocean} in a jar containing CH4-NH3-H-H2O, the early atmospheric gas on earth’s surface. According to Miller Urey, subsequent reactions between these compounds organized a self-replicating RNA molecule- The first life appeared in the earth. Changes in the surface temperature of the earth throughout its history were very important for understanding both the geological development of earth surfaces and origin and development of life in earth. Carl Sagon and Muller G carried out a theoretical investigation of living term changes in the earth temperature on assumption that major infrared absorbing gases in earth atmosphere had always been vapor and carbon dioxide [6]. But in view of accepted boundary condition for early earth, they concluded that the original terrestrial atmosphere must also have contained additional absorbing gases. The earth’s early atmosphere must have gone significant changes in chemical composition as the postulated additional absorbing agency was removed. Secondly, because any physically probable additional absorber was likely to belong to a chemical species that figured in concerning the origin of life. Sagan & Muller considered “The Ammonia” to be the most probable candidate. The surface temperature could be calculated in two stages. The first involved the computation of effective temperature of the planet earth Te-S (1-A) = fóTe4 where S = Solar constant, A = the spherical Abedo of earth, f=the flux factor ó =the steafan Boltzmann constant. For a rapidly rotating planet, with a thick atmosphere, the area of emitting radiation is taken as 4Ï R2 where R= planetary Radius. Since the area receiving solar radiation as 4ÏR2, the flux factor becomes 4. In case of slowly rotating planets with the thin atmosphere, the area of emitting radiation is similarly 2Ï R2 and the flux factor f=2. The second stage of their calculation relates Te to the surface temperature Ts by an equation Ts=Te+ÄT where ÄT was the greenhouse effect in the earth, which also played a vital role in the appearance of life in this planet. On the lifetime of the Earth for the period 4.5 to 4.0 Ga the solar constant (S) had increased by 40- 45%, since the origin of the solar system. If this was to fit into the model Ts = TetÄT, then the surface temperature of the earth was below the freezing point of water during the early phase of earth’s history i.e. the earth had to pass an “Ice Cold Stage also”. But the geological evidence suggest the presence of extended sheet of liquid water on earth’s surface was the pre-requisite condition for appearance of life at least3700MYR ago Carl Sagan and Muller G also suggested that the infant biosphere of earth was warmed by an atmospheric gas which exerted a ‘Greenhouse effect’ by transmitting sunlight while hindering the escape of heat to space. Water vapor made the most significant contribution to the greenhouse effect in that contemporary atmosphere. A sudden fall in temperature could result it an increase in the size of polar ice caps of earth and seasonal snowfields and a corresponding fall in the atmospheric humidity. Both effects would contribute a further drop in the temperature. On the other hand, a sudden rise in temperature increased the water vapor content of the atmosphere.
METHANE AND WATER AREIMPORTANT TO ANY LIFE
Sagan and Muller suggested that early atmosphere was very rich in ammonia gas and this ammonia provided the blanket to keep the Journal of Aerospace Engineering & Technology Volume 9, Issue 1 ISSN: 2231-038X (Online), ISSN: 2348-7887 (Print) JoAET (2019) 30-39 © STM Journals 2019. All Rights Reserved Page 36 earth sufficiently warm for life to emerge. Recent works suggested that the primordial atmosphere probably contained little ammonia but the relatively high partial pressure of CO2. CO2 also acted as blanket gas as greenhouse gas. Whatever the greenhouse gas, ammonia or CO2, mean surface temperature of earth exceeded that time over 500c with a 25% increase in solar heat flux. Now the question stands for CH4 and NH3. However, CH4 (methane) and NH3 (ammonia) might not have been present in the atmosphere of the early earth. Whether methane and ammonia were present or not in primitive earth’s atmosphere were a debatable situation and might depend on whether the oxidation state of the upper mantle of atmosphere varied over time or not. For that required volcanic sources where from methane and ammonia become a significant component of volcanic gas. Yet the volcanic gases were there, the mantle could have been oxidized gradually by recycling of water from the surface to atmosphere and atmosphere to surface, followed by volcanic outgassing of hydrogen. These processes, of course, could have required hundreds of millions of billions of years to bring the mantle to be its present oxidation state. Not by mere 0.7 billion years. So in absence of volcanic sources of methane and ammonia gases, the past history of bombardment atmosphere was probably dominated by carbon dioxide and nitrogen gas with traces of CO, H2, NO, N2, reduced sulpher gas.
FORMALDEHYDE & HYDROGENCYANIDE HOW FORMED
With regard to the origin of life, the key and very important question was whether photochemical reaction in such an atmosphere could have generated Formaldehyde (H2CO) and hydrogen cyanide (HCN)? The formaldehyde was needed to the synthesis of backbone sugar molecule of RNA and HCN was for the synthesis of amino acid for base sequences of RNA nucleotides. Pinto showed that an efficient pathway for formaldehyde synthesis existed even in carbon dioxide dominated atmosphere when these molecules should have readily available [7]. But the formation of HCN was very much and almost difficult because it would require then breaking up both an NßN and a CßC triple bond [if it started N2 & CO2 to form HCN] both bonds can be severed in very hightemperature core of lightning discharge. Yet the resulting N and C atoms are more likely to combine with O2 atoms than with each other unless the atmospheric C:O ratio exceeds unity. However, Zahnle showed that HCN could be formed by ion spherically produced N atoms reacting with photolysis by-product of trace elements (1-10ppm) of CH4 [8]. However such a scenario requires an atmospheric source of CH4. So explaining how HCN could have formed is still a major hurdle for theories of the origin of Life that rely on the atmosphere as a source of starting materials. When one thinks of varied molecular process at the origin of life, one can imagine that the first replicating molecule that brought life on the earth was an RNA molecule. Possibly about 4.6 Billion years ago (Ga) lightning and ultraviolet radiation from the sun were enough to break up simple hydrogen-rich molecule of the primitive atmosphere. The fragments spontaneously then recombined into more and more complex molecules. The products of this early chemistry were dissolved in water of ocean or ponds forming a kind of organic soup, which gradually had an increasing complexity, until one fine day, quiet by an accident? - A molecule arose that was able to make crude copies of it using buildings blocks of their molecules in that soup- which was the master molecule of life – The DNA. It took approx one million years to develop a DNA molecule from RNA molecule in the earth. It was possible that life was largely confined to sea during the Archaean period. In the ocean, the atmospheric partial pressure of CO2 maintained a continuous flux of particulate organic matter for life into the deep ocean. These fluxes resulted from primary production in the surface layers which was limited by the rate of supply of nutrients notably nitrogen and phosphorus, from reverie inputs and from the slow circulation of nutrients-CO2 rich deep ocean water. In 1950 Stanley Muller and Harold Urey did an experiment individually and isolate with all possible primitive gasses present in the early atmosphere of the earth in
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an airtight thick non breakable glass bottle and gave constant electrical sparkling discharge at the glass bottle. After 100 minutes of constant sparkling resulted in a product looking like Tar. It was extremely rich in a collection of amino acids (constituent parts of protein) and nucleic acid and amino acids. But not life.
HOW OXYGEN CAME IN ANATMOSPHERE OF EARTH
Oxygen was nearly absent in the atmosphere of the early earth. Oxygen did not start to build up in the atmosphere probably until about 600 million years ago and it wasn’t until the end of the protozoic era that it started to approach today’s level 21%. It appears before these authors that photosynthetic organisms appeared about 2.2 billion years ago in the earth. At that point, neither the sea nor air of earth contained free oxygen. The oxygen content of the atmosphere then became 1.5 billion ago 1%, at the 600 million year point mentioned above; the oxygen content is thought to have exceeded 6% in 1.5 billion years. This would have been about 50-80 million years before the Cambrian explosion. By relating atmosphere composition to the chemistry of various ancient rocks types, geologists have inferred that earth went from large oxygen-free to oxygen-rich 2.4 billion to 2.5 billion years ago. For some untold eon, more primitive microbes must live the real old fashioned way: anaerobically. These ancient organisms and their “Extremophiles” descendants today thrived in the total absence of oxygen, relying on sulphate for their energy needs. The fossil record shows that cyanobacteria existed about 2.7 billion years ago, leaving scientists to wonder why 200 million to 300 million years of oxygen production by these bacteria resulted in no accumulation of the gas. So photosynthesis would have created a net gain of oxygen first in the ocean and later in the atmosphere. Eventually, with sufficient oxygen in the atmosphere, respiration would have balanced photosynthesis except when burial removed the organic material from the oxygenated water or air. Before oxygen could build up in the atmosphere it must have oxidizes reduced ions in seawater. During the period 2.7 to 2.2 billion years ago, these early bacteria are known as “cyanobacteria” used energy from the sun for photosynthesis, and release oxygen as a byproduct. They also sequestered carbon dioxide in organic molecules.. They do not have a nucleus and reproduce only by cell division. These creatures are the earliest evidence of cellular life on earth. They were the first organisms to develop photosynthesis. Photosynthesis today is balanced by oxygen using respiration. There is a group of one celled organisms that can live in an oxygen free environment. These are the bacteria or prokaryotes. For some untold eons prior to the evolution of these cyanobacteria, during the Achaean eon, more primitive microbes lived the real old fashioned way: anaerobically. These ancient organisms and their “extremophile” decedents today thrived in the absence of oxygen, relying on sulfate for their energy needs. Later the researches also had discovered a possible new species of bacteria that would survive in the early earth by producing and “breathing “its own oxygen. This finding suggests that some microbes could have thrived without oxygen producing plants on the early earth and thus possibly on other planets of our solar system even by using their oxygen to garner energy from methane (CH4). The oxygen producing bacterium provisionally was named Methyolmirbilis oxyfera, could grow in a layer of methane-rich but oxygen-poor mud at the bottom of rivers and lakes of the early earth. These microbes live on a diet of methane and nitrogen oxides, such as nitrite and nitrate. These nitrogencontaining compounds are especially abundant in sediment contaminated by agricultural runoff today. The microbes extract energy from methane through a chemical process linked to Dentification, which releases nitrogen and oxygen from nitrogen oxides. The two known groups of methane-consuming bacteria live either the absence of oxygen (anaerobic methanotrophs) or exploit oxygen from the atmosphere. The M oxyphera can survive in methane-rich areas that are inhospitable to many other bacteria it does with the help of an enzyme perhaps a nitric oxide dismutase that combines
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molecules of nitric oxides to form nitrogen and oxygen. The oxygen is then used to metabolize methane to produce water and carbon dioxide. Figure 3 shows the habitable zones for different types of stars.
CONCLUSION
Most of the known Super-Earths are very close to their orbiting stars, closer than the planet Mercury is to our Sun. Even though these stars don’t burn as brightly as our Sun, the planets are so close they are like burnt cinders flickering close to a fire. For astrobiologists hoping to find alien life, two Super-Earths orbiting the star Gliese 581 [this super-earth was discovered by Michel Mayor of the Geneva Observatory] have the potential for life. Gliese 581, a red dwarf star, with only one-third of the mass of our sun, is cooler than our Sun. Based on their orbit around this star, planets Gliese 581- c [discovered by Stéphane Udry et al on April 4, 2007and Gliese 581-d [discovered by Diana Valencia and her team] are thought to have better habitable conditions, although some think planet “c” might have a run away greenhouse atmosphere like Venus [9, 10] . Gliese 581 c has its mass at least 5.36 times that of the Earth. Gravity on such a planet's surface should be approximately 2.24 times as strong as on Earth. No direct evidence has been found for water to be present in Gliese 581 c, but it is probably not present in the liquid state may be in the form of vapor in the planet's atmosphere, Two years ago, Mayor discovered a planet the size of Neptune and two super-Earths orbiting this star. The newly discovered planet, named Gliese 581 e
(Figure 4),
is now the fourth known planet in this solar system and the lightest, weighing in at only 1.94 Earth masses. It flies around the star at dizzying speed, taking just 3.15 days to complete an orbit. This new planet orbits so close to the star that its water would have boiled away long ago. It is therefore not in the habitable zone (Figure 3). For an amino acid to form all it would take is organic compounds and liquid water An amino acid Glycin, one of the essential ingredients to life on Earth, has been found in a comet in the comet Wild 2, and not the result of terrestrial contamination. But simple the detection of organic compounds will not necessarily mean there's life on a planet, because there are other ways to generate such molecules. It simply means that there are a lot more life-giving chemicals Fig. 3: The Habitable Zones for Different Types of Stars, with our Solar System as an example. As a Planet is pulled in towards its Star, it can be pulled away from the Habitable Zone.
Super-earths (Exo-planets) Bhattacharya et al JoAET (2019) 30-39 © STM Journals 2019. All Rights Reserved Page 39 Fig. 4: Gliese 581 e (foreground) is only about Twice the Mass of our Earth. The Gliese 581 Planetary System now has four known planets, with Masses of about 1.9 (planet e, left in the foreground), 16 (planet b, nearest to the star), 5 (planet c, centre), and 7 Earth-masses (planet d, with the bluish color).Credit: ESO
ACKNOWLEDGEMENT
To diseased late Mr. Bholanath Bhattacharya and late Mrs. Bani Bhattacharya (parents of residence 7/51 Purbapalli, Po-sodepur Dist 24 Parganas (North), Kolkata-110, West Bengal, India for their initial teaching for us about the universe, Big Bang and Pan-spermia Theory.
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Rupak Bhattacharya, Pranab Kumar Bhattacharya, Upasana Bhattacharya, Ritwik Bhattacharya, Rupsa Bhattacharya, Dalia Mukherjee, Oaindrila Mukherjee, Ayshi Mukherjee, Debasis Mukherjee. Super-earths (Exo-planets): How Much Probability of Colonization of Life is There?. Journal of Aerospace Engineering & Technology. 2019; 9(1): 30–39p.
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