Amateur Scientifics

1. Thanks to the Kepler mission, we now know that there are many billions of Earth-sized planets in the Milky Way Galaxy, and its habitable zone of its host star will be discovered very soon.      Kepler mission
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3. Within a decade, we will have a large sample of such exoplanets.
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5. The search for other Earths will then become a hunt for those habitable worlds that are most likely to support life.
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7. It is amazing how much we can learn about exoplanets without actually imaging them. 
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9. It is also amazing how much we can learn about the Milky Way by imaging it in detail at a variety of wavelengths.

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       2   Exoplanets

1. The solar system consists of a wide variety of objects orbiting the Sun. 
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3. The many billions of smaller ones range in size and character, from the rocks in the asteroid belt to the ice moons Europa and Enceladus. more
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5. The largest ones are the planets, and there are only eight of them. mnemonic 
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8. The king of the planets is Jupiter, and it has more mass than all of the others combined. 
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10. Yet this gas giant has no discernable solid surface below its colourful atmospheric features. 
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12. Among the smaller rocky planets, Mars has similarities to Earth, including its polar ice caps, extinct volcanoes, and thin ice clouds. more
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14. However, it has no liquid water on its surface and only a very thin atmosphere consisting mostly of carbon dioxide. more
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17. Among all of these worlds, only the Earth has surface oceans of liquid water, an oxygen-rich atmosphere, and abundant life. 
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19. Is Earth just a rarity in the solar system or a rarity in the entire Galaxy? more
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22. Actually, up until the early 1990s, the only planets known in the entire universe were located in the solar system. 
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24. Since that time, many hundreds of exoplanets have been found around other stars 
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28. using a variety of indirect techniques.
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30.  Image - Our Solar System   best of hundreds here  
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33. Initially, these techniques were only sensitive enough to detect Jupiter-mass exoplanets. more re planets
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36. The Kepler space observatory was launched in 2009 with the primary objective of determining whether Earth-sized planets are common in the Galaxy. more
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38. Kepler detects exoplanets by observing and timing tiny eclipses in the brightness of stars as any satellite exoplanets pass in front. 
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40. During the course of its mission to date, Kepler has detected thousands of exoplanet candidates, of which many are Earth-sized. 
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42. The holy grail in this effort is the detection .. of its host star. 

1. 3   The 51 Pegasi System  wiki etc

1. It has been necessary to develop indirect methods of detecting exoplanets because almost all are too faint to directly image in the glare of their host stars. 
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3. No ground-based or space-based telescope is currently capable of imaging an Earth-sized or Jupiter-sized planet in an Earth-sized or Jupiter-sized orbit around any solar-type star at optical wavelengths.                                                 
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8. The Cassini eclipse image of Saturn more illustrates the problem. In the image, there is a faint point-like Earth just beyond the rings.
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11.                                                    nearest image selected from these
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13. Imagine trying to see it without Saturn blocking the Sun. 
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15. Imagine seeing it from the nearest star 30,000 times farther than Saturn. 
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18.  Only 30 exoplanets (all big and far from a star) have been imaged (mostly using infrared). 
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20. The best case is the H–R 8799 multiple exoplanet system. here
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22. Ground-based detection of the near-infrared emission revealed a system of three exoplanets in 2008 and a fourth in 2010. more
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25. All four planets have masses about 5 times that of Jupiter. The innermost planet has an orbital radius 1.5 times that of Saturn. 
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27. The planets are especially infrared-bright due to the youth (about 30 million years) of the star system. 
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30. The first exoplanet around a solar-type star was found in 1995. more
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32. It just so happens that this star, 51 Pegasi, is only 2.3 degrees on the sky away from H–R 8799 near the     Great Square in the constellation Pegasus more. 
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34. Besides being bright, imaging reveals nothing out of the ordinary. 
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36. It is through spectroscopy that 51 Pegasi yielded a big surprise.
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38. The star exhibited tiny velocity “wobbles,” which are due to the gravitational tug of an unseen orbiting planet.  another result
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41. Data from 51 Pegasi showed 55 meter-per-second shifts to and fro over 4.2 days. 
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43. This is indicative of a 0.5-Jupiter-mass planet 0.05 astronomical units away. 
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45. This “hot Jupiter” is 8 times closer to 51 Pegasi than Mercury is to the Sun. 
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47. This was a surprise because massive planets are expected to form much farther out. 
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50. Was the 51 Pegasi system the oddball, or is the solar system the oddball? 
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52. Most of the initial Doppler exoplanets after 51 Pegasi more are also hot Jupiters. more
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54. But the Doppler method is biased toward such systems. 
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56. Close, massive planets pull harder on stars and have larger velocity shifts. more
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58. They also have shorter periods that are faster to detect. 
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61. As sensitivity has improved, many more less-massive planets have been discovered. Over 500 exoplanets have been detected. more
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4   The Transit Method when a planet transited across a star’s disk

1. Given the limitations of the Doppler approach here, the transit method is  ...........       around a solar-type star. 
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3. Like the Doppler technique, this method is an indirect one, where the exoplanet is not detected through its emission of radiation. 
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5. It involves searching for the small fraction of stars exhibiting periodic drops in their light output due to transiting exoplanets in edge-on orbits to our line of sight.
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8. In June of 2012, Venus provided a close-up example. 
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10. It transited across the Sun’s disk over the course of a few hours. 
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12. We won’t see it aligned again on Earth until 2117. 
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15. The stars are too far away to see as anything but points.
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17. Exoplanets won’t be visible as small, dark disks, but stars will show periodic brightness drops. 
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19. In the case of a solar-sized host star, a Jupiter-sized exoplanet transit dims light 1 percent, and an Earth-sized transit dims light 0.01 percent. 
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22. More than 100 transiting exoplanets have been discovered from ground observation. 
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24. These are mostly all large, close-in exoplanets. 
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26. We need to get above the atmosphere to detect Earth-sized exoplanet transits.
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28. Space also provides continuity for complete orbit coverage. 
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31. The Kepler space observatory was launched by NASA in 2009 with the primary goal of determining if Earth-sized exoplanets are common. more
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33. It is essentially a really big camera designed to take a picture of the same 150,000 stars every 30 minutes in a single part of the sky. 
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35. By monitoring so many stars simultaneously, Kepler  ......................  
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37. Earth-sized exoplanets are common, Kepler is expected to detect hundreds over the course of its multiyear mission. 
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5   The Search for Other Earths 

1. Kepler is the size of a car, with a 1.4-meter mirror.
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3. The heart of the instrument is its 95-megapixel detector array, which consists of 42 charge-coupled devices each with 2200 × 1024 pixels.   
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5. This is equivalent to about 0.3 percent of the entire sky. 
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7. It is located just above the Milky Way to maximize the number of stars without overcrowding. 
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9. Each pixel covers 16 square arc seconds on the sky. 
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12. Kepler was launched into an Earth-trailing orbit around the Sun. 
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14. With no Earth occultations, it falls behind at a rate of about 7 days per year. 
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16. The spacecraft rolls 4 times per year to keep its solar arrays pointed at the Sun. 
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18. It’s always in a position to continue observing.
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20. Because the transit method is most sensitive to large planets ... .....discovered by Kepler were appreciably larger than Earth with periods of a few days. 
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22. If the third similar transit occurs at this period, the candidate is  ???
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25. As of Jan 2013, Kepler has detected 2740 exoplanet candidates as a function of their size and orbital period. In November 2013, astronomers estimated, based on Kepler space mission data, that there could be as many as 40 billion rocky Earth-size exoplanets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way. source  see Q1 under   People also ask
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27. With each yearly data release, there is an increasing number of smaller-sized planets  
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29. ??? convincingly detect the shallow light drops of smaller planets. 
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31. The statistics show that these small planets are common. 
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34. In fact, 20 percent of solar-type stars have ??? a super-Earth with a period of less than 123 than 150 days, while 17 percent of solar-type stars have an Earth-sized planet with a period of less than 85 days.
35. smaller size text due to a PC showing overlapped lines
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38. Over time, Kepler will detect more Earths with longer periods.
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41. The bottom line is that the Milky Way has billions of Earth-sized planets. 
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43. But are these Earth-sized planets actually like Earth? 
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45. The habitable zone is the orbital region where surface liquid water can exist.
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47. Factors include stellar luminosity, planet atmosphere, etc. 
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49. In our present solar system, only Earth is in the habitable zone. 
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51. Earths detected by Kepler so far are closer than Mercury to the host star. 
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53. None of them are in the habitable zone. 
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55. A case in point is the Kepler-20 planetary system, which consists of two Earth-sized planets: Kepler-20e and Kepler-20f. more including Kepler-452b (a planet sometimes quoted to be an Earth.  
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57. They are sandwiched between three larger planets.
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59. $OO¿YHDUHFORVHUWKDQ0HUFXU\WRWKHLUVRODU = a sentence
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61.  All five are closer than Mercury to their solar-star.  The italics represent the original text which, on pasting gives the $OO etc line
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63. The surface temperatures of Kepler-20e and Kepler-20f are about 760°C and 430°C, respectively.  
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67. Kepler-22b orbits 0.85 astronomical units from its solar-type star. 
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69. If its atmosphere is like Earth’s, then it has a surface temperature of about 20°C. 
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71. If its mass and composition are poorly constrained, it could be an ocean world. 
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74. The case of Kepler-22b highlights a key limitation of the transit method: 
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76. It typically does not provide a tight constraint on an exoplanet’s mass, like the Doppler method. 
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78. If both the size and mass of an exoplanet can be measured, its overall composition can be estimated based on the derived density. 
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81. For example, a water world would be bigger than a similar-mass rocky planet. 
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83. Depending on the water world temperature, it might be a steam world, ocean world, or ice world. 
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85. Our best bets for life would be warm rocks or ocean worlds of approximately Earth’s size.
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88. There is a current list of 25 potentially habitable exoplanets. more
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90. However, none are Earth-sized; all are super-Earths. more
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92. Most—18 of the 25 - are Kepler exoplanets candidates with size only. 
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94. Over 70 percent of such candidates were eventually confirmed. Omitted 
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96. The Kepler map of Earth-sized planets as of January 2013 shows that all are too close to their host stars to be habitable. 
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98. But soon, more Earth-sized planets will be found further out. 
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100. Some of those will be in the habitable zone with known masses. 
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102. The map will become a target list of warm rocks and ocean worlds. 
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105. A future telescope will be able to take infrared spectra of these exoplanets. 
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107. Such spectra will allow studies of their atmospheres. 
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109. We can then compare them to those of Earth, Venus, and Mars. 
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111. This could reveal water, ozone, methane, carbon dioxide, etc.  
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113. Furthermore, they could provide strong evidence of life.