Habitability of Planets - Literature review Example

Habitable Planets Name Institution Course Unit Instructor Date According to astronomers, Earth is no longer the only habitable planet. In the last several years, space exploration has led to the discovery of several other planets and systems that possess the needed environment to support simple to complex life forms. Basically, hospitable planets should possess enough atmospheric pressure to support water in its liquid state on the surface and bearable temperatures. These conditions exist in a belt called the circumstellar or Galactic habitable zone (CHZ or GHZ) or simply the life zone (Abe, 2001). It is estimated that this belt contains over 40 billion earth sized planets orbiting sun-like stars in the Milky Way (Klotz, 2013). The Milky Way is just one of the many galaxies that feature a huge star with strong gravitational pull that makes several celestial bodies to revolve around it. Therefore, the earth is part of a system of planets orbiting around the sun that are part of the larger Milky Way galaxy. The Milky Way Galaxy is also orbiting a galaxy core. In the last few years astronomers have suggested that there are other planets in other galaxies capable of supporting life. To be hospitable, planets must have the right conditions needed to support life. Other than atmospheric pressure and presence of water, there are many other factors that make a planet habitable. Atmospheric pressure and temperature greatly influence the presence of water which basically supports life as is known to human beings. One should keep in mind that man’s understanding of life is based on his own experience and knowledge that basic life forms need air, energy in whatever form and water to survive. Whether there are any possible life forms that can exist beyond the normal temperature range of earth and without the assumed supporting elements of life is yet unknown. Therefore, the habitability of planets in this case assumes that current life forms on earth such as bacteria, plants and humans can exist in such environments (Heller, 2015). Life supporting environment should also possess sources of energy and nutrients. In the solar system, the main source of energy is the sun in form of sunlight. For planets closest to the sun, Mercury and Venus, there is too much energy from the sun that keep the temperatures very high such that water cannot exist in liquid state while those further away the energy is just too little to support life (Abe, 2001). The earth falls in the CHZ that has the moderate temperature and sunlight. The radiation from the sun to nearby planet is also at dangerous levels. The atmosphere comes in handy in filtering the radiation from the sun. Significant amount of atmosphere amount in form of concentration and width with the right composition of gases is needed to support life. Normally, the bigger the planet, the more massive the atmosphere it can acquire and maintain courtesy of its gravitational forces. Therefore, smaller planets have weak gravitational forces and hence little atmosphere and thus are less likely to support life (Horner, Nicholson & Carter, 2015). Another issue that determines habitability of planets assumed in the GHZ is the distance of the galaxy from the galaxy core. Galaxies close to the Galaxy cores are exposed to massive infrared radiation from the galaxy core meaning that they are at risk. Therefore, where the planets in the GHZ in sun-like star systems are theoretically in the GHZ, the proximity to the galaxy core overrides this provision. The solar system is located at a safe distance from the Milky Way Galaxy’s core that makes the GHZ in the system habitable (Horner, Nicholson & Carter, 2015). . Figure 1 The CHZ of the solar system (source: http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/habzone.htm) Additionally, for a planet to be habitable, it must orbit a star that has remained stable in billions of years. The orbiting must also be in a circular motion to ensure that conditions of the planet remain stable throughout the year. A stable star means that its energy output is guaranteed to remain constant in order to support life. Stars similar to the sun possess enormous amounts of energy such that any fluctuations in the amount of energy emitted could have devastating effects on nearby bodies such as planets. In the case of the solar system, the sun has remained stable for billions of years. Solar flares, which are huge explosions as a result of suddenly released energy accumulated over time, pose a huge threat to life on nearby planets and life forms. NASA estimates that a solar flare is equivalent to 100-megaton hydrogen bombs exploding at the same time (Solar flares, 2015). Such explosions in major space bodies lead to release of materials. These materials may gather to over millions of years of time to form new bodies as stars or planets. Previously, scientists believed there were only nine planets. They included Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. However, recent studies enabled by technology and deep space exploration have led to better understanding of space and general behaviors of planets and other bodies. For instance, better understanding of the behavior of the solar systems planets led to the declassification of Pluto as a planet into a dwarf planet thus reconstituting the solar system into eight planets (Pluto loses status, 2015). The same approach has also led to the discovery of billions of other planets and galaxies with some billions of light years away. While the solar galaxy, which contains the sun and the eight planets, is the most recognized galaxy, billions of other galaxies have been discovered but details about them are scant. However, scientists estimate that planets in these galaxies that orbit the sun-like stars and fall within the same distance as the earth is from the sun or the GHZ may support life. In the earth Solar system, Earth and Mars are the most habitable planets. The habitability of Mars is still under research. However, there are important statistics available that suggest habitability. For instance, Mars’ gravity is 38% that of the Earth's. Although there is no liquid water on Mars, there is evidence to suggest that it can be extracted from its surface. Other notable habitable planets in alien galaxies include Kepler-186f, HD 40307g and Gliese 163c. Figure 2 The Kepler 186 system (source NASA) Kepler-186f is one of the most recently discovered planets in an alien galaxy. The planet is named after NASA's Kepler Space Telescope which has been used to discover numerous new planets and hence the name. The earth-sized planet exists in the GHZ and hence meets some of the basic requirements of habitability. First the planet is almost the same size of earth meaning that its gravitational forces could be similar to that of earth and hence able to maintain a significant atmospheric layer. The planet is part of the Kepler-186 system, which is about 500 light-years from Earth in the constellation Cygnus, and lies in the systems GHZ. The Kepler-186 system also lies at a safe distance from constellation’s core meaning that it is stable. The system also contains other dwarf planet but they do not fall within the GHZ (Culler, 2015). Gliese 163c is another potentially habitable planet orbiting the red dwarf Gliese 163 contained in the Dorado constellation. The planet is located approximately 49 light-years, or 465 trillion kilometers and is approximately ten times the mass of earth. With such a huge mass, the planet’s gravitational pull is enormous though astronomers still think it can still support life. The Gliese 163 also system is relatively small with only three confirmed planets hence the term red dwarf. The planet takes just 26 days to orbit the dwarf star, a fact that triggered huge debates on its habitability among astronomers. The smaller size of the red dwarf in comparison to the sun means that the star produces significantly less energy and heat meaning that its GHZ is comparatively closer to it that the earth is to the sun (Redd, 2012). The third planet that is potentially habitable is the HD 40307g in the HD 40307 system. This system is 42 light-years away in the constellation Pictor. In comparison to the sun, the systems HD 40307 star is smaller and less luminous. There are only three confirmed planets orbiting this star which is not visible from the earth as a star due to its relatively smaller size. However, the planet HD 40307g is way much larger than the earth seven times over. Just like the earth and Mars, the planet has a rocky surface. Research on this planet is continuing to understand better its characteristics and potential to support life. Again, research is more oriented towards discovering planets and systems closer to the solar system as they can be better observed (Tate, 2012). As it has been highlighted above, majority of these potentially habitable planets and constellation are millions of kilometers away. At the current technology levels, there are no available space ships that can reach these planets to enable closer observation. For this reason, some researchers have often critiqued these claims on potentially habitable planets based on the mere fact that the claims cannot be verified but are only validated by theory. Another issue that has plagued and even fuelled the search for other potentially habitable planets and alien life forms is unidentified Flying Objects (UFO) claims. For a very long time the media, more so the internet and film, has fuelled claims of UFO being cited in many locations around the world. Whether there are alien life forms or not is yet to be verified and the best option at the moment s continuous space exploration. References Abe, S. (2001). Galactiv habitable zones. Retrieved from https://astrobiology.nasa.gov/articles/2001/5/18/galactic-habitable-zones/ Culler, J. (2015). Kepler-186f, the First Earth-size Planet in the Habitable Zone. Retrieved from http://www.nasa.gov/ames/kepler/kepler-186f-the-first-earth-size-planet-in-the-habitable-zone Heller, R. (2015). Planets more habitable than earth may be common in our galaxy. Scientific American 312(1): 32-39. Horner, J. Nicholson B. & Carter, B. ( 2015). What makes one earth-like planet more habitable than another? Retrieved from http://www.iflscience.com/space/what-makes-one-earth-planet-more-habitable-another Klotz, I. (2013). Galaxy hosts 10 billion 'habitable' earth-size worlds. Retrieved from http://news.discovery.com/space/alien-life-exoplanets/galaxy-hosts-10-billion-habitable-earth-size-worlds-131104.htm Pluto loses status as a planet. BBC News. Retrieved from http://news.bbc.co.uk/2/hi/science/nature/5282440.stm Properties of planets in habitable zone (n.d.) Retrieved from http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/habzone.htm Redd, T. (2012). Newfound alien planet a top contender to host life. Retrieved from http://www.space.com/17684-alien-planet-gliese-163c-extraterrestrial-life.html Tate, K. (2012). Super-earth planet: potentially habitable alien world explained (Infographic). Retrieved from http://www.space.com/18390-super-earth-exoplanet-habitable-zone-infographic.html Wall, M. (2012). The top 5 potentially habitable alien planets. Retrieved from http://www.space.com/16728-top-5-habitable-alien-planets-countdown.html What is a Solar Flare? (2015). Retrieved from http://hesperia.gsfc.nasa.gov/sftheory/flare.htm Read More

Life supporting environment should also possess sources of energy and nutrients. In the solar system, the main source of energy is the sun in form of sunlight. For planets closest to the sun, Mercury and Venus, there is too much energy from the sun that keep the temperatures very high such that water cannot exist in liquid state while those further away the energy is just too little to support life (Abe, 2001). The earth falls in the CHZ that has the moderate temperature and sunlight. The radiation from the sun to nearby planet is also at dangerous levels.

The atmosphere comes in handy in filtering the radiation from the sun. Significant amount of atmosphere amount in form of concentration and width with the right composition of gases is needed to support life. Normally, the bigger the planet, the more massive the atmosphere it can acquire and maintain courtesy of its gravitational forces. Therefore, smaller planets have weak gravitational forces and hence little atmosphere and thus are less likely to support life (Horner, Nicholson & Carter, 2015).

Another issue that determines habitability of planets assumed in the GHZ is the distance of the galaxy from the galaxy core. Galaxies close to the Galaxy cores are exposed to massive infrared radiation from the galaxy core meaning that they are at risk. Therefore, where the planets in the GHZ in sun-like star systems are theoretically in the GHZ, the proximity to the galaxy core overrides this provision. The solar system is located at a safe distance from the Milky Way Galaxy’s core that makes the GHZ in the system habitable (Horner, Nicholson & Carter, 2015). . Figure 1 The CHZ of the solar system (source: http://ircamera.as.arizona.

edu/NatSci102/NatSci102/lectures/habzone.htm) Additionally, for a planet to be habitable, it must orbit a star that has remained stable in billions of years. The orbiting must also be in a circular motion to ensure that conditions of the planet remain stable throughout the year. A stable star means that its energy output is guaranteed to remain constant in order to support life. Stars similar to the sun possess enormous amounts of energy such that any fluctuations in the amount of energy emitted could have devastating effects on nearby bodies such as planets.

In the case of the solar system, the sun has remained stable for billions of years. Solar flares, which are huge explosions as a result of suddenly released energy accumulated over time, pose a huge threat to life on nearby planets and life forms. NASA estimates that a solar flare is equivalent to 100-megaton hydrogen bombs exploding at the same time (Solar flares, 2015). Such explosions in major space bodies lead to release of materials. These materials may gather to over millions of years of time to form new bodies as stars or planets.

Previously, scientists believed there were only nine planets. They included Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. However, recent studies enabled by technology and deep space exploration have led to better understanding of space and general behaviors of planets and other bodies. For instance, better understanding of the behavior of the solar systems planets led to the declassification of Pluto as a planet into a dwarf planet thus reconstituting the solar system into eight planets (Pluto loses status, 2015).

The same approach has also led to the discovery of billions of other planets and galaxies with some billions of light years away. While the solar galaxy, which contains the sun and the eight planets, is the most recognized galaxy, billions of other galaxies have been discovered but details about them are scant. However, scientists estimate that planets in these galaxies that orbit the sun-like stars and fall within the same distance as the earth is from the sun or the GHZ may support life. In the earth Solar system, Earth and Mars are the most habitable planets.

The habitability of Mars is still under research. However, there are important statistics available that suggest habitability.

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