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Note - Below writeup may not be winning writing. You can write much better essays than below sample. These are just guidelines for your preparation. You can read more information and include in your essay on the day of competition.

References for reading

Sample Essay on Probabilities of Life on Other Planets

Is there life anywhere else in the vast cosmos? Are there planets similar to the Earth? For centuries, these questions baffled the curious mind of human being because either the positive or the negative answer, if found any day, would carry a deep philosophy to our very existence in the universe. Scientists have been studying the planets of our own solar system for more than 50 years, looking for evidence of past or present life, among other things. Launched in 1967, the Soviet Union's Venera 4 was the first probe known to land on and send back data from another planet. Since then, astronomers have discovered so many exoplanets of different varieties that our knowledge and understanding about planets have been revolutionized and we are possibly on the verge of getting an answer. During the last two decades, about 4000 extra-solar planets have been discovered. The discovery of a variety of exoplanets and planetary systems has not only revealed that there exist planets about 10 times heavier than Jupiter but also put the solar system in a unique status. While we know well about the five kinds of planets in our solar system, the discovery of at least 18 kinds of extra-solar planets poses great puzzle regarding the physical properties, atmospheric chemistry, internal geology etc. Scientists of various countries have been active in discovering these exoplanets by using ground as well as space bound telescopes and sophisticated instruments. Extensive theoretical work and numerical modelling of the evolution scenario of these exoplanets have revolutionized our concept on planetary science.

Discovering thousands of planets beyond our solar system counts as a “eureka” moment in human exploration. But the biggest payoff is yet to come: capturing evidence of a distant world hospitable to life. The discovery of thousands of planets orbiting nearby stars has nevertheless greatly increased speculation that there may be some kind of life on a planet outside our solar system.

In an infinite universe, most scientists agree, the odds of life existing on a planet besides Earth are pretty high. It is unlikely, however, that familiar life forms will be found on any planet within our solar system. Life as we know it—everything from single-celled organisms to human beings—consists largely of liquid water. So a planet that harbors life can't be too cold or water will freeze, nor can it be too hot or all the water will evaporate. Planets closer to the sun than Earth are too hot, and those farther away are too cold. The surface of Venus, for example, is hot enough to melt lead, and would vaporize any living thing, while the surface of Mars is frozen solid.

Life as we know it here on Earth also requires a magnetic field and an atmosphere, both of which protect it from the lethal radiation our parent star, the sun, emits. Earth's magnetic field—generated by its rotating iron core—deflects the solar wind, a continuous stream of high-speed, high-energy particles coming out of the sun. (As those particles careen by the edges of Earth's atmosphere, they sometime create the phenomenon we call the Northern Lights.) Without the magnetic field there, the solar wind might destroy all life on Earth. As for Earth's atmosphere, it protects life because the water, carbon dioxide and other gases in it absorb solar radiation in its harmful ultraviolet-light form. The parent stars of other solar systems would emit radiation as well, and the planets orbiting them would need the same kind of protection. Of course, life on Earth also alters the chemical composition of the atmosphere—Earth's atmosphere lacked gaseous oxygen until plants started growing here some million years ago. So molecules like oxygen in the atmosphere of another planet would be one indication—not proof—that there are living things there.

The ones most likely to harbor life would be smallish, rocky planets like Earth. Larger planets tend to be composed of hydrogen gas, the most abundant element in the universe, and to not have a solid surface. Good candidates for life would also occupy what scientists call the habitable zone—the zone in which a planet's distance from the parent star makes liquid water possible. The Kepler mission—a space observatory launched by NASA in 1997 to search our galaxy for just these kinds of Earth-like planets—has found one candidate that meets both requirements, Kepler-452b. So the chances of life on another planet are high. However, we have no direct evidence yet of life anywhere other than Earth.

When we find life, how will we know?

The answer has a lot to do with rainbows. As Isaac Newton recognized, white light shot through a prism (or through curtains of mist seen with the sun at your back) is exposed for what it really is: a band of color spanning violet to red, characterized by “wavelength.” Chemicals and gases in the atmospheres of planets can absorb certain slices of this band, called a spectrum, and leave behind a narrow black gap. When we analyze light shot by a star through the atmosphere of a distant planet—a technique known as spectroscopy—the effect looks like a barcode.

Exoplanet missions like Mars or Moon mission is other way to search for life on other planets. NASA's Mars rover, has been sending back reams of data about the red planet since it landed there 12 years ago. Living well past all expectations, Opportunity not only transmits landscape photos and the occasional tweet, but also collects and analyzes soil and atmosphere samples. It's been an invaluable research tool, but has found no direct evidence that life ever existed on Mars, and has revealed that the planet's atmosphere is too thin to protect it from the sun's radiation. Same is true about Moon.

The real question is, will we ever find the planet we're looking for, given that we'll have to survey the planetary systems of the universe's estimated 1 billion trillion stars? And if we do find that planet, will we even recognize the life it harbors? There's no real reason why we should expect to discover life as we know it orbiting a star many light years away from our home solar system. There's so much we don't know that we are severely limited in our ability to even think about the question.

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