Background
Even before the beginning of the space age, astronomers and researchers have attempted to discover whether or not there were other habitable planets like Earth in outer space; discovering other planets like Earth could ultimately answer the question of whether or not we are alone in the universe. With the advancement of aerospace technology, NASA and other organizations have begun to organize efforts to develop more concrete answers as to the possibility of life on other planets. Prior to 2009, no planets had been definitively identified outside our solar system until nearly twenty years ago (NASA Ames Research Center, 2014). As of 2004, we knew of only about one hundred planets that orbited other stars, most of them being gas giants that are of similar or larger size than Saturn (Koch et al. 2004, 1).
However, with these new telescopes and scientific resources, including mathematical formulas and statistical analysis, these experts are discovering hundreds, if not thousands, of new planets outside our solar system every day, including ones that lie in the “habitable zone” (HZ) that permits the climate conditions that can produce life similar to that of Earth’s (Koch et al. 2004, 1). The Kepler spacecraft was launched in 2009 in order to survey one particular segment of the Milky Way Galaxy, looking for extrasolar planets that are of similar size and distance to their sun (and which could, therefore, possibly host organic life). Its mission has been ongoing for nearly five years, and is currently on an extended mission through 2016 to discover even more worlds that could host life.
Goals
The goals of the Kepler mission are fairly straightforward; first, the primary goal of Kepler is to figure out how many terrestrial-sized planets or larger are within the HZ or many different spectral varieties of stars. Kepler’s goal is to look specifically for planets that are approximately the size of Earth, which constitutes planetary bodies that are 1/300th the size of Jupiter, with an orbit firmly in the HZ (where an orbit around their star takes approximately one year) (Koch et al. 2004, 1). In addition to that, the Kepler spacecraft is also tasked with detecting planets of many different sizes, as well as stars of varying types (Koch et al. 2004, 1). One of the larger goals set by the Kepler mission is to determine how many stars in the Milky Way galaxy actually have planets in their HZ (Koch et al. 2004, 1).
Other goals of the Kepler mission include figuring out the size distribution of the planets they find, as well as see which semi-major axes they have. Another goal includes coordinating this data with Doppler spectroscopy and the Space Interferometry Mission (SIM) to look for more larger companion planets, and learning the varying properties of unmoored stars that are not found within planetary systems (“Kepler Overview,” 2014). When the Kepler mission was started, it was estimated that the instrument would need to observe at least 100,000 stars with solar characteristics, with approximately 5000 fitting the requirements of the mission. The expectation was to find at least 25 Earth-like planets, though null results were also stated to be significant (Koch et al. 2010, 3).
Observations
Kepler has one single instrument contained within it, consisting of a photometer that acts as a recorder of the variations in light between the over 100,000 stars that it will encounter over the course of its mission (Koch et al. 2004, 2). Data is collected through this photometer alone, as it does not have a camera with which to take images (Koch et al. 2004, 2). The photometer consists of a telescope with 42 charge coupled devices (CCD) mounted on the telescope’s focal surface, which measures the variations in stellar brightness which should help to determine whether planets are present in the photometer’s view (Koch et al. 2004, 3). The photometer itself is able to rotate 90 degrees on its axis four times a year; this is meant to keep the heat device pointed at deep space, as well as keeping its solar panel array in the direction of the Sun in order to charge its batteries (Koch et al. 2004, 4). As data is collected, only the pertinent data is saved (the specific pixels of the light changes on stars of interest), organized into a 15-minute accumulation, encoded and processed on board, so that it can be downloaded every four days to NASA specialists at Mission Control (Koch et al. 2004, 4).
Analysis
Once the data is delivered to mission control at the NASA Ames Research Center, the data is analyzed in order to interpret the data sent from the Kepler spacecraft. For the most part, the data management center (DMC), located at the Space Telescope Science Institute (STScI), processes the data in order to create a calibrated set of data, measured in flux units, for every pixel that is thought to be interesting along the photometer’s focal plane (Koch et al. 2004, 7). This data is also archived so that the general scientific community can access it. Co-investigators (Co-Is) perform follow-up observation in the even Kepler experiences a threshold-crossing event; the goal for this is to prevent false positives and make sure the data is internally consistent (Koch et al. 2004, 8). Follow-up observation essentially has other instruments, both in space and on the ground, take a look at the stars that Kepler points out as being of interest, so that it can be determined how big each star is, the temperature of the planets that orbit it, and whether or not these factors mean that the planet is within the HZ and of habitable size (Koch et al. 2004, 8).
Conclusions
Through Kepler’s five years as an active program, the results have been very interesting. More than 700 planets have been found and recorded by the Kepler craft so far, though only several dozen of those qualify as being within the HZ (Chang, 2014). The vast majority of them are gas giants, and therefore inhabitable. Of the 715 new planets that the Kepler mission has found so far, they have been found to orbit 305 stars, which also demonstrates the possibilities of solar systems like ours, with multiple planets orbiting around it (NASA Ames Research Center, 2014). Many of the planets found are smaller than Neptune, but still larger than Earth by almost fourfold. With the Kepler’s current mission progress, scientists and astronomers can identify nearly 1700 planets outside our solar system (NASA Ames Research Center, 2014). Already, initial data from the Kepler spacecraft has shown at least five transiting planets, with measured orbits, masses and radii, as well as substantial data from stars at various points of their life cycle, the ability to differentiate between dwarf and red giant stars, and insights into the variability of dwarf stars (Koch et al. 2010, 10).
Of particular interest is the recent discovery of planet Kepler-186f, which researchers indicate is the most Earth-like planet Kepler has yet detected (Chang, 2014). The planet circles a red-dwarf star, and is located 500 light years from Earth; it is also 10% bigger than Earth in size, and it is thought it contains liquid water. While its star is less bright and large than ours, and the planet has a 130-day year instead of our 365-day year, it has at least a somewhat similar temperature to Earth (though it is slightly cooler than our averages) (Chang). With the discovery of planets like these and more, it is possible to have a better understanding of how we fit into the larger scheme of our galaxy.
Future Work
Despite initially only being launched for a 3 ½ year mission, the Kepler mission has been extended until possibly 2016, due to the successes that have been achieved (Clark, 2012). Because of Kepler’s ability to successfully chart exoplanets and stars, and its mission to estimate how many of these exoplanets potentially have life on them, the extension of the mission through 2016 is meant to increase the project’s chances of doing so (Clark, 2012). These mysteries remain to be solved, as well as the greater questions of the existence of life on other planets, and the Earth’s relation to the rest of the Milky Way galaxy.
Comments
The Kepler mission is significant for many reasons; first and foremost, it is one of the most successful space-based projects to date, and one of the few that is still ongoing. In order to make sure interest in space is cultivated within the public, projects like Kepler must continue. Because of the current lack of interest in space travel and astronomy in the general public, and the wane of NASA’s popularity and public exposure, as well as reduction/elimination of funds in recent federal budget cutbacks, it is a dire time to be an astronomer or someone interested in space travel. Things like the Kepler Mission, by having such long-term goals and continued results that can be measured and reported on, will help to keep hope alive for a renewed interest in space travel, and maintain newsworthy stories about space in the public eye.
Furthermore, in a more direct sense, Kepler is helping to create a greater sense of context for Earth’s place in the universe, by helping us see how many other planets like us are out there, and whether or not we are extremely rare by having the right conditions for supporting life. The quest to find life on other planets must start by finding planets that are even capable of doing so, and the Kepler is our primary means of doing so for right now. While its mission is extended for only another year or two, perhaps its mission can be extended further, or other craft can be sent out to cover other areas of the Milky Way in order to further this very important task.
References
Chang, Alicia. “Newfound Earth-Like Planet, Kepler-186f, Is 'Best Case' For Hosting Life,
Astronomers Say.” AP, Apr 17, 2014.
Clark, Stephen. “Kepler Planet-Hunting Mission Extended Until 2016.” Spaceflight Now, April
4, 2012. http://www.spaceflightnow.com/news/n1204/04kepler/.
Koch, David G., et al. “Overview and status of the Kepler Mission.” SPIE Conference 5487
(2004).
Koch, David G., et al. "Kepler mission design, realized photometric performance, and early
science." The Astrophysical Journal Letters 713.2 (2010): L79.
NASA. “Kepler Overview.” NASA.gov.
<http://www.nasa.gov/mission_pages/kepler/overview/#.U15-dfldWSo>. Apr 28, 2014.
NASA. “NASA’s Kepler Completes Prime Mission, Begins Extended Mission.” Press Release
12-394, Nov 14, 2012.
NASA’s Ames Research Center. “NASA’s Kepler Mission Announces 715 New Worlds.”
Astronomy Magazine.
<http://www.astronomy.com/news/2014/02/nasas-kepler-mission-announces-715-new-worlds>. February 26, 2014.
