Humans have been living on earth for quite some time and been very fortunate to be able to make progress and create civilizati

A New World Out There

Joshua Christian Nathanael

U1320096D

Aerospace Engineering

The Earth is Becoming Uninhabitable

Humans have been living on earth for quite some time and been very fortunate to be able to make progress and create civilization that until now is still striving for advances. Since their existence, humans have used their mind to come up with ingenious discoveries and inventions to get over the barriers of problems and take control of nature and earth. As time kept flowing, humans kept refining their abilities and their activities were becoming more diverse than just hunting, eating, sleeping and keeping the human species alive by creating generations. Jumping forward to the present, humans are now spread all over the earth with new generations keep popping up here and there, and their activities taking its toll on earth as effect of their means in fulfilling their ever increasing needs. If this situation persists, the earth will be no longer habitable for humans as all the space is filled up and the environment is no longer suitable.Human population has been exploding in number for over the last three hundred years. As humans keep working in advancing their technology, humans find ways to keep themselves alive longer and extend their life-span such as inventions and development of weapons for protecting themselves from danger, and discoveries in medicines and use of modern technology for preventing and curing diseases. As an effect, the death rate has fallen to 13 over 1000 over the last three hundred years, while the birth rate remains the same at about 30 over 1000 (Raven, Johnson, Mason, Losos & Singer, 2011). The problem is that a human takes up space. When there are more human, the space required increases. If human population continues to grow, the number of humans living on earth approaches infinity, which means they will need infinite space. But earth is not infinitely big. Even when shelters have been built from underground, underwater to the highest skies, if humans keep their population growing, all the space available will be used up. Unless there is a mass destruction, humans will have to find a new place to live to place new generations there.The earth is also becoming uninhabitable due to human activities that cause global warming. To keep the production line fulfilling humans need, resources from nature are drained out such as through mining and deforestation that will physically ruin the earth, and then they are processed to be what are needed. This production line takes up energy that comes from burning fuel which means there is gas emission, such as carbon dioxide. This gas emission becomes greenhouse gases that, according to Henson (as cited by Padget and Dunning-Davies, 2008), absorb heat radiation and blocking it from escaping to outer space. The more greenhouse gas there is, the more heat is absorbed and the warmer the earth is. Without it, the average temperature of the earth would be around -18C. But if the greenhouse accumulates exceeding a normal limit, global warming will occur when there is too much heat absorbed in the atmosphere and the temperature will be too warm for humans, as exposure to temperature above 35C for a sufficient time leads to hyperthermia because dissipation of metabolic heat becomes impossible (Sherwood & Huber, 2010).If the present table is not turned, the earth will be uninhabitable because humans will have lived in every possible corners of the earth and no more space for new generations to be in. Or the earth will be too warm because of global warming due to human activities and all the greenhouse gas that trap too much heat for humans to bear as it accumulates over the years. Either way, the time is drawing near for humans to find a new place to live after living through eras and developing their civilization through the years. It is only appropriate to consider alternative options, look beyond and make plans to build a new world out there for the future.What Humans Need

Now that the notion of finding a new habitat for humans other than earth is up, a set of requirements is needed to decide what kind of place which would be suitable for human lives. In the solar system, the earth is special because it has the right conditions to start life, sustain and support it for million of years, while the other planets do not. Therefore any new place cannot be chosen easily without considering whether it has what humans need to live in. The new world out there will need to have source of water, the right temperature, the right atmosphere, the right mass, and also conditions where nutrition can be produced.First of all, the new place needs to have a source for water. Water has special a special molecular structure that makes hydrogen bonding possible which give rise important properties. One of them is high heat capacity, which means it takes much heat to raise a little temperature. Therefore, planets with water covering their surface will have more stable environment as the temperature around the waters doesnt fluctuate much due to waters high heat capacity (Kasting, 2010). Moreover, water is essential in human survival as it is solvent for many molecules and medium for reactions in the body. Water is so important that human will die of dehydration without it in days. But water in human body can be lost such as through exhaling breath, sweating and urination and loss of water needs to be balanced with intake of water (Popkin et al., 2010). Therefore water availability is important to support human lives.

Next, the new place needs to have the right range of temperature. One of special property of the earth is its perfect distance from the sun, such that the heat intensity received is just right for human lives to begin and flourish. While the other planets are either too close to the sun and ending up too hot or too far from the sun and ending up unbearably freezing. As McNab explained (cited by Sherwood & Huber, 2010), in humans, their body temperature is maintained around 37 C and their skin temperature is regulated to be less than 35 C, because there needs to be heat flowing from body, resulting from metabolic processes, out to the surroundings. When the skin temperature is sustained above 35 C, heat from inside human body cannot flow out and heats up the body itself which is undesired. On the other hand, too cold of an environment will cause hypothermia, which is when the body temperature is less than 35C. When body temperature falls below 28C, the body cannot move and appears to be dead with fixed dilated pupils and no more temperature regulating process. (Francis, 1998) Therefore, humans cannot live in environment with extreme temperatures. Even if humans may be able to extend their tolerance to temperature using equipments and suits with advanced technology, they still have their limitations and the choice for a new place to live is still limited due to temperature extremities.The new place for humans to live will also need to have a suitable atmosphere. First it needs to contain oxygen gas for respiration and for human bodies to produce energy. Moreover, planets whose atmosphere contain oxygen gas also can have ozone layers as they are created from oxygen gas, so planets containing oxygen gas can protect humans from ultraviolet radiation which is harmful. Another gas that is important is nitrogen gas. If the new places atmosphere contains abundant oxygen gas but no nitrogen gas, fire will burn more rapidly as there is no nitrogen gas that brings heat without making the fire bigger, whereas oxygen gas makes the fire bigger. In addition, nitrogen gas prevents water vapor to rise up higher in the atmosphere by diluting water vapor near the surface of the earth, so that theres little water vapor concentration difference between lower and higher atmosphere. If water vapor rises up to the higher atmosphere, the water molecules are dissociated into hydrogen and oxygen atoms by ultraviolet photons from the sun (photodissociated) and hydrogen atoms will escapes to space while oxygen atoms stay. In the end, they cannot form back into water and therefore water is lost (Kasting, 2010).The new place will also need to have the right mass and gravitational force that comes from the mass of the place. The earth has hot liquid core that is rotating under our feet due to earths rotation. This moving hot liquid core contains metallic nickel-iron alloy which induces earths magnetic field. This magnetic field protects earths atmosphere from sputtering, where charged particles come from outer space and collide with ions in the atmosphere which can lead to loss of atmospheric gas. If earths mass were smaller, the hot liquid core would cool down more quickly and solidify, then there would be no more planetary magnetic field, putting earths atmosphere in jeopardy and risk of a loss. Other than affecting the hot liquid core, a planets mass also affect how its atmosphere is pulled by gravitational force and reducing the effect of sputtering. Mars is an example of planet which has smaller mass than earths and lacks planetary magnetic field. The two properties cause Mars to have atmosphere thinner than earths. On the other hand, when the new place has a mass too large, i.e. bigger than 10-15 earths mass, it will have gravitational field so big that gas is pulled onto the new place and accumulate to form a gas giant like Jupiter, the biggest planet in the solar system (Kasting, 2010). Therefore, for the new place to be habitable for humans to stay, it shouldnt have a mass too small nor too big.Nutrition is also important for human lives and the new place will need to have a condition where food can be produced. Humans need food as a source for energy and raw materials that human bodies cannot produce on their own (Raven et al., 2011). Energy can be obtained from food containing carbohydrates, proteins and fat. Proteins are also source for amino acids bodies which are important for protein synthesizing in our body, such as in producing enzymes, structural proteins, carriers of oxygen among others. Our bodies produce some amino acids but there are other amino acids that are not produced in human and they can only be gained from food. Other than carbohydrate, protein and fat as macronutrient, humans also need micronutrient such as vitamins and minerals. Even though they are needed only a little compared to macronutrients, deficiency of them will be troublesome and cause symptoms or even diseases. For instance, vitamin A deficiency causes dry eyes and night blindness, and iodine-deficiency disorders causes slow motor and cognitive development and growth failure in children (cretinism), and swelling of thyroid gland in the neck (goitre) (Geissler & Powers, 2011). Therefore, other than humans, other living organisms such as plants and animals will also need to be able to survive in the new place because human bodies cannot synthesize their own nutrition but they obtain nutrition from food which comes from plants and animals. The new place will need to be able to support not only human lives, but also lives of humans sources for nutrition.

In deciding whether a place is habitable or not, there are properties which should be considered so that humans can survive living in that new place. Humans will need to sort out and limit their choices according to their criteria for survival. In the end, their choices will need to have water, suitable temperature, atmosphere and mass, and also conditions where plants and animals, as source of nutrition, can live.The Search

The criteria are lined up, the candidates are spread all over the universe, and all there is to do is to find the golden needle in the gigantic haystack. Rather than searching for one place after another that will fulfill all of the criteria, the search prioritizes planets that have water on the surface rather than hidden underneath as in Mars. Such planets are said to be in the liquid-water belt, the region around a star where liquid water can be maintained on the planets surface. The planets with liquid on its surface may support life and therefore the planets are also called to be in a habitable zone. According to a work by Michael Hart, as James Kasting (2010) explains, the habitable zone around a star changes as time passes because stars evolve to be brighter and therefore the habitable zone goes farther outward. But initial and final habitable zone may overlap and these overlapping areas are called Continuous Habitable Zone (CHZ). Massive stars with mass larger than that of sun burn and become brighter faster and therefore habitable planets do not stay in CHZ for a long time, whereas stars with mass smaller than suns have extremely narrow or even non-existent CHZ. Moreover, planets that orbit such lightweight stars are tidally locked, or in other words the planets always show the same face to the star, just like the moon shows the same face to the earth. This causes the planets to have one side to always have daytime while another side to always have nighttime. The atmosphere and ocean at night will freeze and atmosphere and ocean from the day diffuse to the night. The freezing and dispersion continues until all of them are frozen into the night. So for a start, stars with mass close to the sun are put on top of humans search list.

There are two ways in searching for planets in the universe. First is the indirect detection, which includes the following:

(1) The Astrometric Method

In astrometric method, a star and planets are rotating around a common centre while this centre is also moving in space. If the star has planets around it, the star will be observed from afar to be wobbling around the track of the common centre in space. How big is the wobbling depends on how massive the planets that rotate the star. If the wobbling of the star can be determined, then the planet which is rotating can be determined in terms of its mass. But a planet with earths mass can only wobble the star a little and there is not yet equipment powerful enough to detect it.(2) The Radial Velocity Method

The radial velocity method is method in detecting planets by calculating Doppler shift of the wavelength of a stars absorption line. Every star emits light of various wavelengths, and also absorbs light of certain wavelengths. If the star moves back and forth relative to an observer, the observed stars absorption of light will also shift back and forth due to Doppler Effect. This effect can be observed when the star is moving back and forth quickly, implying that there are planets with great mass orbiting close to the star. Since this also depends on the stars wobbling motion, this method is not very effective in finding a planet with mass similar to that of earth.(3) Using gravitational microlensing

For gravitational microlensing, imagine a star and earth, with another star in between. The light from the star at the end of alignment will be focused by the middle stars gravity to the earth according to Albert Einsteins theory, and this light appears to be a ring which is called, as you expect, the Einstein ring. If the brightness of the ring is plotted in a graph, it should give a smooth curve. But when the middle star has planets orbiting around, the graph would have bumps because the planets would contribute in focusing the light too. This method is still new as in 2010 and only 8 planets have been discovered with this method, compared with over 290 planets discovered using the radial velocity method (Kasting, 2010), but nevertheless, it is possible to detect earth-like planets using gravitational microlensing.(4) Utilizing transits.

When the passing of a planet in front of a star is observed, a transit has been observed. From observing a transit, the properties, such as the size, of the planet that passes can be inferred from the drop of stars observed brightness. But transits dont occur very often, as it has the odds directly proportional to the stars radius and inversely proportional by the distance between the star and the planet. Since the new planet and the new star should be in similar size to the earth and sun, the odds of finding such transit is small.

Other than observing the star, it is possible to observe the planets atmosphere by observing transits. If the planet has an atmosphere, some wavelengths of light from the star will be absorbed by gases in the atmosphere, and spectrum can be created to show absorption of every wavelength and thus it is possible to infer components of the atmosphere according to wavelength absorbed. This method is called primary transit spectroscopy. There is also secondary transit spectroscopy, where the spectrum of light from a star and a planet, side by side, is recorded. Then the spectrum of light from the star only is recorded. By subtracting the first and second spectrums, earths spectrum can be obtained.

Another way to find planets in the universe is the direct detection. In this way, the planet is observed directly rather than observing wavelengths or brightness of the star which the planet orbits just like in indirect way. But the planets brightness is overshadowed by the stars brightness, which becomes a trouble in observing the planet directly. But there has been ways to get through such problem and be able obtain a spectrum of wavelengths from the planet:

(1) Infrared Interferometers

First is by using more than one telescope in space to detect light with thermal-infrared wavelengths from a planet. The ability of a telescope to detect a star and a planet apart is directly proportional to the employed wavelength and inversely proportional to the telescopes size. Light with thermal-infrared wavelength has a relatively long wavelength, therefore the telescopes has to be large to function effectively. But using more than one telescope, the devices size is now the distance between adjacent telescopes and the ability is the same with only one gigantic telescope.(2) Using a coronagraph

Second is by using a coronagraph with the telescope to detect light with visible wavelengths from a planet. The light with visible wavelengths from the star is much brighter than that from the planet and if the telescope is used without the coronagraph, the reading will be dominated by light from the star. But with a coronagraph, the light from the star is suppressed and the telescope can detect light from the planet and the resulting reading will show the spectrum of light from the planet.(3) Using a visible occulter

The third is by using a visible occulter which is essentially a shade that covers the telescope from the stars light. Instead of using a coronagraph to suppress light from the star, a visible occulter or a shade is used to do the same task. The shade is flown out of the telescope and at the right distance, the light from the star is blocked by the shade and the telescope can detect light from the planet.With all the available methods in hand, humans can start searching for planets which can be their new place to live. Humans can find planets and stars in outer space and discover their properties such as size of the star, size of the planet and the planets atmosphere. The discovery will determine whether that planet is suitable to support human lives. The chance may be very slim, but with all the stars in the night sky, there may be one or two spots that are just right and can be a new world once humans are out there.ReferencesFrancis, J. (1998). (1998). Immersion hypothermia [Supplement], South Pacific Underwater Medicine Society Journal, 28(3). Kasting, J. (2010). How to find a habitable planet. Princeton, United States: Princeton University Press.Popkin, B.M., DAnci, K.E. and Rosenberg, I.H. (2010). Water, hydration, and health, Nutrition Reviews, 68(8): 439458.Pudget, L. and Dunning-Davies, J. (2008). Some comments on the possible causes of climate change. Retrieved from http://arxiv.org/abs/0806.3418.Raven, P.H., Johnson, G.B., Mason, K.A., Losos, J.B. and Singer, S.R. (2011). Biology (9th ed.). New York, United States: McGraw Hill.Sherwood, S.C. and Huber, M. (2010). An adaptability limit to climate change due to heat stress, Proceedings of the National Academy of Sciences of the United States of America, 107(21): 95529555.