For centuries now, humankind has attempted to solve the mystery underpinning the possibility of human life beyond the Earth. This has resulted in numerous attempts of space exploration. Recently, the discoveries of several planets that are orbiting stars have resulted in intense excitement and renewed the interest for the quest to discover other planets that could support human life (Gene, 2010). At present, there exists substantial evidence confirming existence of three main categories of exoplanets, which include ice giants, hot-super-earth going round in short period orbits, and gas giants. However, the main challenge involves finding terrestrial planets the size of which is half of the earth, particularly those that are located within the habitable zone of their orbital stars wherein there is a possibility of existence of liquid water (Lemonick, 2012). There is a mounting controversy surrounding the issue of whether extraterrestrial life is a possibility.
Attempts to explore the possibility of extraterrestrial life can be classified into three broad categories: searches on the Earth’s solar system, explorations of the possibility of life in other solar systems, and the search for life adventure. With regard to explorations in our solar system, scientists have explored the solar system using probes targeting land or orbit on target planets. A case in point is the ongoing attempts by scientists to explore the possibility of life on Mars. With regard to explorations of other solar systems, ground-based, and space-based telescopes (particularly the Keller observatory) have been used to discover existence of several extrasolar planets with a specific interest on exoplanets that are situated within the habitable zone of their main or parental star (Kasting, 2010). The thinking underpinning exploration of other solar systems is that the existence of a potent solvent is capable to bring forth life by enabling molecules to interact with one another, which in turn can create long chains that constitute building blocks that make up life. The search-for-life adventure has been adopted by a number of astronomers such as the Search for Extraterrestrial Intelligence (SETI). This method of explorations relies on the use of radio telescopes to identify any radio signals that are likely to be broadcasted by an intelligent civilization in space. At present, these astronomers have not detected any form of extraterrestrial activity in their explorations (Miller, Vandome, & McBrewster, 2010).
In a quest to discover the possibility of extraterrestrial life, the Kepler Mission was designed with the primary objective of exploring our region in our galaxy (the Milky Way) in order to unveil a number of earth-size planets that are within the habitable zone. In addition, the Kepler Mission has the objective of determining how many stars in the Milky Way have planets that can sustain life. So far, the Kepler Mission has managed to trace the position of our solar system within the larger continuum of the planetary systems found in the Milky Way (National Aeronautics and Space Administration, 2013). The primary objective of this paper is to explore both scientific and political aspects of the Kepler Mission.
Kepler Mission’s Scientific Goals and Objectives
The primary scientific objective of the Kepler Mission entails the exploration of the diversity and structure of the planetary systems found in our galaxy. In order to achieve this objective, Kepler Mission has outlined a number of goals to facilitate the mission. They include (National Aeronautics and Space Administration, 2013):
- Goal 1: To determine abundance and frequency of larger and terrestrial planets found within or adjacent to habitable zones of their parent stars. With regard to this goal, the frequency of planets can be computed from the size and number of planets detected and from the spectral type and the number of stars that are being surveyed. In such case, a null outcome will still be extremely significant because of the relatively large number of stars being surveyed and the relatively low rate of false alarm.
- Goal 2: To determine how the shapes, orbital semi-major axes and sizes of these extrasolar planets are distributed. With respect to this goal, the planet’s area can be computed using the stellar area and the decrease in fractional brightness. The semi-major axis of a planet can be computed using the stellar mass and the measured period by utilizing Kepler’s third law.
- Goal 3: To estimate the orbital distribution and frequency of the extrasolar planets found in the multiple-stellar systems. This goal can be attained through a comparison of the number of planetary systems found in multi-stellar and in single systems. Ground-based spectroscopic measurements having high angular resolutions can be used in the identification of multiple stellar systems.
- Goal 4: To determine distributions of density, mass, size, albedo and semi-major axis of short period giant planets. The detection of short-period giant planets can be done by assessing the variations emerging from their reflected light. Similarly, the semi-major axis can be computed using the stellar mass and the orbital period. Transits are likely to be observed in approximately 10 percent of the cases, after which the planet’s size can be calculated. After determining the planet size, the amplitude of the reflected light modulation and the semi-major axis can be used in the computation of the albedo. The density of the planet can be computer after observing the planet in transit (to derive its size) and using the Doppler spectroscopy (in determining the mass of the planet for stars having mv >13 and a temperature that is cooler than F5.
- Goal 5: To identify the extra members of the revealed planetary systems that have been discovered photometrically by use of complimentary techniques: Surveying to extra massive companions that do transit can be done through observations facilitated by ground-based Doppler spectroscopy and the Space Interferometry Mission (SIM), which helps in the observation of greater details of the planetary systems that have been discovered by the mission.
- Goal 6: To determine the properties of the stars that host the planetary systems that have been discovered. With regard to this goal, ground-based observations can be used to determine the metalicity, luminosity class and the spectral type of the stars in transit. In addition, stellar activity, surface brightness inhomogeneities, and rotation rates can be computed directly using photometric data. Asteroseismology (Kepler p-mode measurements) can be used to compute the stellar mass and age.
It is imperative to note that the mission, goals, and objectives of the Kepler Mission are consistent with NASA’s objectives of the Space Interferometry Mission, the Terrestrial Planet Finder, and the Original theme missions. This is because Kepler Mission will play instrumental role in the identification of common stellar attributes for the host stars for planet explorations in the future; help in defining the space volume required to survey; and offering a target list for SIM wherein systems have already affirmed the existence of terrestrial planets (Space.com, 2011).
The Investigation Process under Kepler Mission
An overview of Planet Formation
The complexity underpinning how planets and stars were formed is undeniable, which makes nearly unfeasible to determine the variations among planetary systems using first principles. A number of contemporary theories point out that planetary growth commences with small solid grains found in circumstellar disks, which are assumed to be an integral part during star formation and have been observed to surround several young stars (Kasting, 2010). This is followed by stars colliding and agglomerating to form larger bodies that produce planets. Gas giants are derived from adequately massive bodies that accrete relatively larger hydrogen amounts while smaller planets form from condensed matter. In the light of this view, planets are anticipated to have common characteristics and have varying planet masses and sizes (Space.com, 2011).
A number of factors determine the features of a given planetary system. These include torques between the surrounding disks and the growing planets, growth and sticking of the relatively small grains, viscosity and turbulence in the disks comprising of dust and gas, and the chemical and physical processes associated with the magnetic fields. At present, there is no theory can be used to accurately determine how frequent the planets form or how the orbits and planetary sizes are distributed (National Aeronautics and Space Administration, 2013). Nevertheless, one theory stipulates that dynamic instabilities observed in accretion disks form the Jovian mass planets. Another common theory elucidates the formation of extraterrestrial planets that develop to become relatively large to attract a substantially massive envelope of gas. It is imperative to note that large cores can be observed in the second scenario and not in the first scenario.
At present, it can be argued that theory is the most valuable methodology that astronomers can use to extrapolate from known systems. However, theoretical models that draw upon a single instance of our own Solar System have failed to state whether the Solar System is anomalous or typical. The detection of short-period giant planets through the results of Doppler spectroscopy points out the differences between our Solar System and a number of solar-like stars systems (National Aeronautics and Space Administration, 2013). Nevertheless, these surveys have been unable to discover large numbers of extrasolar planets. Under the Kepler Mission, planetary transits are detected using space-based photometry, which offers relatively greater sensitivity than ground-based photometry when detecting smaller and terrestrial planets. Since space-based photometry provide data relating to the orbital periods and sizes of smaller and terrestrial planets that orbit diverse stellar types, the results from the Kepler Mission facilitate the positioning of our own Solar System within the range of the planetary systems found in our galaxy and facilitate the development of theories basing on the empirical data collected (National Aeronautics and Space Administration, 2013).
There are several factors that determine whether a planet is habitable or not, with the most accepted definition of a habitable planet being that it must have liquid water at the surface. The presence of liquid water at the surface of the planet depends on the stellar type (the effective temperature and size of the star and respective orbit of a planet (Space.com, 2011). These criteria can be used to define the habitable zone for any given star. Planets that are located interior to the habitable zone (nearer the parent stars) tend to be extremely hot, which results in surface water boiling and vaporizing away; a case in point is Mercury. Planets that are located outside the habitable zone are extremely cold, which results in the surface water being frozen constantly; a case in point being Mars. For the case our solar system, the habitable zone lies between the orbits of Mars and Venus.
The second significant factor that determines habitability of a planet relates to its mass and size. Planets that often form having less than 25 percent of the mass of Earth do not have adequate surface gravity that can create a life sustaining atmosphere; a case in point is Mars. On the contrary, planets that form with masses that are 10 times the mass of earth have adequate surface gravity that can hold even the most abundant and lightest elements, helium and hydrogen; as a result, they develop into gas giants; examples of this include Neptune, Uranus, Saturn and Jupiter (National Aeronautics and Space Administration, 2013). Therefore, the goal of Kepler Mission to detect the habitable planets needs the mission to identify planets that have masses that fall between 1.5 to 10 times the mass of earth, basing on the assumption that terrestrial planets have a similar composition and density of about 07-2.0a Earth radii. Other factors that affect the habitability of a planet include the composition and amount of the atmosphere since it offers cosmic ray protection and UV and determines the temperature. The impacts of giants and moons in a given planetary system are also vital because they safeguard the planet from asteroid and comet impacts (Space.com, 2011).
The Transit Method that the Kepler Mission Uses to Detect Extrasolar Planets
Kepler Mission uses the transit photometry technique for planet detection. A transit refers to the process of a planet crossing in front of its parent star as observed by an observer. According to Gene (2010), transits by extrasolar planets often result in a small change in brightness of the star by about 1/10,000 (100 parts per million) that lasts for about 1-16 hours. Gene (2010) reports that this change should be specific, especially if it is caused by a planet in transit. Furthermore, all transits resulting from the same planet should result in a similar change in brightness and should last for the same period of time. therefore, resulting in a signal that is repeatable and can be detected easily. After its detection, the size of the planet can be computed using the mass of the star and the orbital period by applying Kepler’s Third Law of Planetary Motion (Lemonick, 2012). Planet’s size can be computed using size of the star and the depth in transit, which refers to a decline in brightness of the star. The characteristic temperature of the planet can be computed using the temperature of the parent star and the size of its orbit. As aforementioned, knowledge about the temperature of a star is vital in assessing habitability of a planet since planets having moderate temperatures are the only ones that can sustain life as on Earth (Miller, Vandome, & McBrewster, 2010).
Based on the above discussion, it is apparent that three parameters can be used to describe the characteristic of a planet in transit. These include duration of the planetary transit, the fractional change regarding the brightness of the star, and the time period it takes for the transit to reoccur, which is the orbital period for the planet. The orbital period for the planet (p) is used in the computation of the semi-major axis, provided the stellar mass (M*) is known, which is determined by the star’s spectral type. Kepler’s Third law of planetary motion is the used in the computation of the semi-major axis as shown below:
The transit duration can be computed using the formula below:
Where a* denotes the diameter of the stellar in solar diameters and M* denotes the mass of the stellar in stellar masses whereas a refers to the semi-major axis of the orbit in AU. However, the transit duration does not provide any meaningful information that can be used to gauge the physical characteristics of the planet, but the transit duration needs to be constant for all the transits for a particular star-planet combination. If this is not the case, then it is highly likely that there are several planets in the planetary system being detected. This might also mean that there are non-transit activities occurring in the system (National Aeronautics and Space Administration, 2013).
With regard to transit depth, the fractional change in the brightness of the planet can be equated to the ratio of planet’s area to star’s area. Miller, Vandome, & McBrewster (2010) points out that this ratio is helpful to compute planet’s size if the size of the star is known depending on the spectral type of the star, which can be determined using ground-based observations of that particular star. Asteroseismology, which involved studying star oscillations, is a more precise technique that can be used to determine stellar mass (Kasting, 2010).
As mentioned above, Kepler Mission utilizes the Transit Photometry technique to detect extrasolar planets. According to Gene (2010), transit photometry technique functions by measuring periodic dimming of the parent star, which is caused by a planet trajectory path in front of the parent star, which is often in the line of sight of a ground observer. However, the size of the planet that can be detected is limited to the half the size of the earth because of the variations in stellar time scale. In addition, planets having orbital periods that are more than 2 years cannot be detected readily; this is because their probability of being aligned properly in the observer’s line of sight to the parent star is relatively small. In the figure 1 below, the orbits and the full range of masses of extrasolar planets that the Kepler Mission can discover are shown in the white region. Giant outer planets generating a transit signal of about 1 percent but have orbital periods that are more than 2 years can be detected by follow up using either ground-based photometry or Doppler spectroscopy. Giant planets found in inner orbits can also be detected regardless of their orbit alignment; this detection is facilitated by their periodic modulation associated with their reflected light. For about 10 percent of giant planets having transits, the density of the planet can be computed using a combination of the transit depth and the mass derived from Doppler data. Astrometry and Doppler spectroscopy can be helpful in surveying for giant planets that found in planetary systems detected using photometry. Owing to the fact that the orbital inclination should be near 90 degrees (sin i = 1) for transits to occur, it is highly likely that mass of the giant planet will be detected (Space.com, 2011).
Figure 1: detection limits for planets that are around solar-like stars
Source: National Aeronautics and Space Administration. (2013). Kepler: A Search for Habitable Planets. Retrieved February 14, 2013, from http://kepler.nasa.gov/Mission/QuickGuide/
Overview of the other Methods for Detecting Planets
Besides transit photometry, other techniques that can be used to detect extra solar planets include pulsar timing, Doppler spectroscopy and astrometry. Pulsar timing was the first commonly accepted technique for detecting extraterrestrial planets. The mass of the earth and other smaller planets that orbit a pulsar were discovered through calculating the periodic variation with regard to the pulse arrival time. However, this method can only be used in the detection of planets that orbit a pulsar (dead star) and not a dwarf star (Kasting, 2010). Another limitation of this method is that it assumes that planets were likely formed following the supernova, which leads to the pulsar. According to this view, the formation of planets is perceived to be somewhat a common phenomenon rather than a rare one.
Doppler spectroscopy is mainly used in the detection of the stellar spectrum’s periodic velocity shift resulting from a giant planet that is orbiting. Using ground-based observations, astronomers can quantify Doppler shifts that are greater than 3m/second because of the reflex motion of a solar-like star. Astrometry can be used to survey for periodic wobble induced by a planet with regard to the position of the parent star. Astrometry relies on ground-based observations (Kasting, 2010).
The Design of the Kepler Mission
The criteria for a planet to transit, as observed in our solar system, is that its orbit should be lined up edgewise to an observer on the ground. The probability that an orbit will be aligned properly can be computed by dividing the star’s diameter by the orbit’s diameter. This is about 0.5 percent for a planet transiting in an earth-like orbit revolving around a Sun-like star. For the case of giant planets whose orbits equal to four days, the probability of alignment is about 10 percent. Detecting several planets requires one to survey not just a hundreds of stars, but thousands of stars in transit. For the case of Kepler Mission, about 100,000 stars are searched so that even if earth-like planets are rare, then a null outcome would still be valuable. In the event that Earth-like planets are extremely common, then the Kepler Mission will be able to detect several hundreds of them (Lemonick, 2012).
Taking into consideration that Kepler Mission has the main objective of finding planets that are located within the habitable zones of their parent stars such as the Sun, the time between two transits is approximated to be one year. In order to consistently identify a sequence, an observer requires four transits; as a result, the duration for the Kepler Mission should be at least 3.5 years. In the event that the duration for the Kepler Mission is extended, then it is highly likely that the mission will detect distant and smaller planets and a relatively larger number of planets that are similar to the Earth (Kasting, 2010).
The instrument used in Kepler Mission (referred to as Kepler Instrument) is a telescope having a 0.95-meter diameter, which is known as a light meter or photometer. The specially designed telescope has a relatively large field of view compared to most astronomical telescopes. The Kepler instrument requires a larger field of view because it is used in surveying a relatively large number of stars. In addition, the Kepler Instrumental observes one star field during the entire mission while simultaneously and continuously monitoring the brightness of at least 100,000 stars for a period of at least three and half years. The figure below shows the Kepler instrument used for the mission (Lemonick, 2012).
Given the nature of the mission, there is the need for the diameter of the specially designed telescope to be sufficiently large in order to lessen the noise emanating from the photon counting statistics; this enables the Kepler Instrument to quantify a small change in the brightness when the planets are in transit. The Kepler Instrument should be space-based in order to ensure that it has a photometric precision that can facilitate the observation of an earth-like transit and to circumvent interruptions resulting from day-night cycles, atmospheric perturbations and seasonal cycles such as the extinction limitation linked to ground-based observations. According to NASA, extending the Kepler Mission beyond the initial time frame (3.5 years) will facilitate the detection of planets having relatively larger periods; finding planets that are located around parent stars that are noisier because more variability or being fainter; and help in the detection of smaller planets.
Anticipated Results of the Kepler Mission
The Kepler Mission commences data collection immediately following its launch and checkout and embarks on reporting the outcomes in a progressive manner. The Kepler Mission reported its first results a few months after launch when the giant inner planets having short orbital periods (few days) were observed. Planetary objects in Mercury-like orbits having orbital periods of a few months were identified during the first year of the mission (National Aeronautics and Space Administration, 2013). However, earth-like planets transiting in earth-like orbits need almost the entire mission’s time although there are cases where in three transits can be observed in at least two years. Other results of the Kepler Mission that need about four years of data collection include: (a) planets that are relatively small (size of Mercury) and have short orbital periods; the detection of this planets need more transits to be detected; and (b) detecting giant inner planets not transiting the parent star but have periodic modulations on their brightness because of the light that is reflected from the planet. According to NASA, the most thrilling discovery following the launch of the Kepler Mission ought to be the discovery of earth-size planets found in the habitable zones of solar-like parent stars. Nevertheless, NASA is prepared for several other discoveries regarding the features and occurrence of extraterrestrial planets that transit around stars. NASA reports that even if Kepler Mission finds few or no extraterrestrial planets, the results will be meaningful since it would result in the conclusion that extraterrestrial planets are rare and that there is the need to reconsider the origins of the Earth.
Assumptions Used in the Estimation of the Results
One of the strengths underpinning the Kepler mission relates to the ability of the mission to handle any unanticipated occurrence; this stems from the capability of the Kepler Instrument to monitor relatively large samples of stars in order to gather statistically significant data relating to larger and terrestrial planets that have orbital periods that range from about a few days to at least one year (National Aeronautics and Space Administration, 2013). Therefore, the Kepler Mission is only capable of estimating the results using possible scenarios because there is knowledge relating to the distribution and frequency of the extraterrestrial planets located outside our solar system. In this regard, the Kepler Mission has been designed in such a manner that a null outcome would still be significant and the data can be used in deriving important conclusions relating to our solar system. In order to quantitatively assume the outcomes of the Kepler Mission, the following assumption were used (National Aeronautics and Space Administration, 2013):
- The Kepler Instrument will monitor 100,000 main sequence stars;
- The mean variability of white light (based on a timescale of a transit) for most of the F-,K-, and G- main sequence stars is the same to that of the Sun;
- The probability of transit for extraterrestrial planets found within or near the habitable zone is 0.5 percent for each planet;
- There is one giant planet found in the outer orbit for each star;
- The detection efficiency is approximated to be 84 percent and one false detection is anticipated; and
- The full duration for the Kepler Mission is 4 years.
Summary of the Anticipated Results
Basing on the above description of the Kepler Mission as well as the assumptions regarding the detection criteria, considering only four transits during a period of about three and half years, considering stellar variability and presuming that planets are prevalent around starts such as the case of the sun, the Kepler Mission team anticipates to detect (National Aeronautics and Space Administration, 2013):
- For terrestrial inner-orbit planets depending on their transits
- Approximately 50 planets in case most planets have R ~ 1.0 Re
- Approximately 185 planets in case most planets have R ~ 1.3 Re
- Approximately 640 planets in case most planets have R ~ 2.2 Re
- For giant inner planets basing on the periodic modulation as a result of their reflected light:
- Approximately 870 planets having orbital periods that are less than a week
- For giant planets basing on their transits
- Approximately 135 inner-orbit planets together with albedos for about 100 of these detected planets
- Densities for approximately 35 of the inner orbit planets
- Approximately 30 outer-orbit planets
Political Aspects of the Kepler Mission
The main political aspects regarding the Keller Mission revolves around the funding of the mission, especially following the extension of its duration by extra 3.5 years to 2016. It is undeniable that since its launch, Kepler Mission has been a success. Besides planet hunting, the Kepler Mission has delivered paradigm-changing data regarding the nature of the stars and our understanding of the planetary system. However, the primary challenges for the Kepler Mission is time and funding (Miller, Vandome, & McBrewster, 2010). NASA asserts that time is not a setback for Kepler Mission on grounds that if the Kepler instruments stares for longer periods, it increases the chances of identifying smaller planets. Nevertheless, the main setback is not time, but funding. Space.com (2011) reports that getting the mission’s managers at NASA to extend the operations for the mission for additional 3.5 years may be costly. The total cost for the mission was about $ 600 million and it would require an additional $ 17 million to keep the mission’s operations going. At present, the spacecraft is in a perfect condition and that adequate consumables are on board that can last for the extended time. Lemonick (2012) points out that these are turbulent times for NASA; this is because of the significant schedule and cost overruns by the James Webb Space Telescope, which is threatening to gulp a significant portion of the space science budget for NASA. The worst case scenario was when the Congressional budgeteers suggested not only canceling the James Webb Space Telescope but also slashing at least $ 1.9 billion from the NASA’s 2012 fiscal budget under the Obama administration. A number of scholars have criticized the Kepler Mission on grounds that large projects tend to eat up a significant portion of funds and cut into other important programs (Space.com, 2011).
With NASA operating under a tight budget, numerous concerns were raised that the Kepler Mission will not be continued following its scheduled time despite being one of the most successful astrophysics missions. The Astrophysicists were faced with the challenge of convincing the government that the mission be extended and they needed adequate funding for the mission to be extended. However, funding for such extensions often impose repercussions on a number of continuing projects (Lemonick, 2012). For instance, NASA will be forced to close out the Spitzer infrared project in 2015. The Senior Review of Missions under NASA is done after two years in order to help NASA maximize on the scientific productivity of the missions that are currently operational. During the Review, missions are often prioritized and ranked depending on the level of success. In the previous review, funding for about 10-20 percent of the extended missions was removed because of either substantially reduced capabilities or fractional instrumental failures. However, the 2012 review found all the missions undertaken by NASA to be successful, which pose a dilemma on the Kepler Mission on whether to extend the program or not. With the extension of Kepler Funding, a number of missions currently undertaken by NASA were affected in various ways. For instance, the Fermi operations were extended to 2016 although with a 10% annual cut in funding starting from 2014; funding for Hubble Space Telescope will be maintained although at the current funding levels (Lemonick, 2012).
According to Lemonick (2012), it is a moral imperative for the government to fund the extension of the Kepler Mission. Discovering life outside planet earth is likely to alter the manner in which humankind perceives life. Lemonick (2012) maintains that discovering extraterrestrial life is a far-reaching landmark in human history compared for the moon-shot. However, with the need to extend the Kepler Mission, two other vital proposals under NASA, the Space Interferometer Mission and the Terrestrial Planet Finder, have been suspended permanently. This is because of the delayed James Webb Telescope, which is eating up substantial amounts of NASA’s space budget, yet the United States’ budgetary situation is currently bleak.
During the dilemma of extending the Kepler mission and the subsequent funding of that extension, several scholars suggested a number of avenues through which such funding; for instance, Lemonick (2012) suggests that the funding for the project could be obtained from an international source. In this regard, Lemonick (2012) argues that stopping the funding for the Space Shuttle Program resulted in an increased reliance on supranational rocket science; therefore, there is the need to promote a supranational economy to fund such large projects instead of posing the strain on domestic economies. Kasting (2010) argues for voluntary funding rather than taxing the citizenry for the Kepler Mission. Private funding has also been suggested by Lemonick (2012) in order to cater for the costs of extending the project and other future projects. Nevertheless, the common agreement is that extending the project was vital.
This paper has discussed scientific and political aspects of the Kepler Mission. The primary scientific objective of the Kepler Mission entails the exploration of the diversity and structure of the planetary systems found in our galaxy. In order to achieve this objective, Kepler Mission has outlined a number of goals to facilitate the mission, which include: (a) Determining the abundance and frequency of larger and terrestrial planets found within or adjacent to the habitable zones of their parent stars; (b) determining how the shapes, orbital semi-major axes and sizes of these extrasolar planets are distributed; (c) estimating the orbital distribution and frequency of the extrasolar planets found in the multiple-stellar systems; (d) determining the distributions of density, mass, size, albedo and semi-major axis of short period giant planets; (e) identifying the extra members of the revealed planetary systems that have been discovered photometrically by use of complimentary techniques; (f) determining the properties of the stars that host the planetary systems that have been discovered. Kepler Mission utilizes the Transit Photometry technique to detect extrasolar planets. Transit photometry technique functions by measuring the periodic dimming of the parent star, which is caused by a planet trajectory path in front of the parent star, which is often in the line of sight of a ground observer. However, the size of the planet that can be detected is limited to the half the size of the earth because of the variations in stellar time scale. In addition, planets having orbital periods that are more than 2 years cannot be detected readily; this is because their probability of being aligned properly in the observer’s line of sight to the parent star is relatively small. The instrument used in Kepler Mission (referred to as Kepler Instrument) is a telescope having a 0.95-meter diameter, which is known as a light meter or photometer. The specially designed telescope has a relatively large field of view compared to most astronomical telescopes. The Kepler instrument requires a larger field of view because it is used in surveying a relatively large number of stars.
With regard to political aspects of the Kepler Mission, it is apparent that the mission faced constraints linked to the extension of the duration and its subsequent funding. The total cost for the mission was about $ 600 million and it would require additional $ 17 million to keep mission’s operations going. At present, the spacecraft is in a perfect condition and that adequate consumables are on board that can last for the extended time. With NASA operating under a tight budget, numerous concerns were raised that the Kepler Mission will not be continued following its scheduled time despite being one of the most successful astrophysics missions. Astrophysicists were faced with the challenge of convincing the government that the mission be extended and they needed adequate funding for the mission to be extended. However, funding for such extensions often impose repercussions on a number of continuing projects.