1. The Search for Another Earth

2. Exoplanets and the Kepler Space Telescope An exoplanet or extrasolar planet is a planet that orbits a star other than the Sun. The first confirmation of an exoplanet orbiting a main- sequence star was made in 1995, when a giant planet was found in orbit around the nearby star 51 Pegasi. Some exoplanets have been imaged directly by telescopes, but the vast majority have been detected through indirect methods such as the transit method and the radial- velocity method.

3. The Search for Another Earth Exoplanet Exploration NASA's and ESA’s Exoplanet Exploration Program represent science and missions of unprecedented scope and ambition, promising insight into humankind's most timeless questions: Where did we come from? Are we alone? The primary goal of these explorations is to discover and characterize planetary systems and Earth-like planets.

4. The Search for Another Earth The Challenge There are over 100 billion suns in our own Milky Way galaxy to search. Exoplanets: - Don't produce any light of their own, except when young - Are an enormous distance away from us - Are lost in the blinding glare of their parent stars.

5. The Search for Another Earth The Challenge Advances in data-gathering technology and analysis capabilities now provide scientists with the advanced tools and capabilities to enable this exploration of our galaxy. Observation from highly specialized spacecraft supported by ground-based telescopes has become the primary method used.

6. The Search for Another Earth The Kepler Spacecraft Carrying a telescope specifically designed for the search for exoplanets, Kepler has been the workhorse of this effort. Kepler's goal is the creation of a statistical survey that predicts how many Earth-like planets likely exist in our galaxy. The spacecraft was launched into a solar Earth-trailing orbit in March 2009.

7. The Search for Another Earth The Kepler Spacecraft Kepler is in a heliocentric or Sun- centered orbit. This unusual “Earth-trailing” orbit allows Kepler continuous observation of its target stars. Kepler’s region of study is in a very star-rich part of our Milky Way galaxy, far enough north of the plane of Earth's orbit that neither Earth nor the Sun will encroach on Kepler's field of view.

8. The Search for Another Earth Where is Kepler looking? Kepler is pointed in a region of the sky near the constellations of Cygnus and Lyra. The space telescope constantly monitors over 150,000 stars watching for the presence of an exoplanet passing in front of a star. Staring at these stars, Kepler’s specialized instruments measure the changes in light intensity over time using the “transit method” of detection.

9. The Search for Another Earth What is Kepler looking at? Kepler is looking at the Cygnus region along the Orion arm centered on galactic coordinates: 76.32º,+13.5º or RA=19h 22m 40s, Dec=+44º 30' 00'. The star field is far enough from the ecliptic plane so the Sun does not shine into the telescope at anytime during the year. This field of view virtually eliminates any occultations by asteroids and Kuiper-belt objects, which commonly orbit near the ecliptic plane.

10. The Search for Another Earth Transit Method of Planetary Detection If a planet passes directly between a star and an observer's line of sight, it blocks out a tiny portion of the star's light, thus reducing its apparent brightness. Sensitive telescope instrumentation can detect this periodic dip in brightness. Sensitive telescope instrumentation can detect this periodic dip in brightness. From the period and depth of the transits, the orbit and size of the star’s planetary companions can be calculated.

11. The Search for Another Earth Transit Method of Planetary Detection If a planet passes directly between a star and an observer's line of sight, it blocks out a tiny portion of the star's light, thus reducing its apparent brightness. Sensitive telescope instrumentation can detect this periodic dip in brightness. Sensitive telescope instrumentation can detect this periodic dip in brightness. From the period and depth of the transits, the orbit and size of the star’s planetary companions can be calculated.

12. The Search for Another Earth Confirming What Kepler Sees The next step is to confirm the findings. One method used to confirm the findings is to measure the “wobble” of the star which tells the extent of movement induced by a planet's gravitational tug. Another method is to measure the “doppler shift” of the star’s light frequencies as it moves slightly with the exoplanet’s orbit. From these observations, scientists can estimate the mass, density and potential make-up of the planet.

13. The Search for Another Earth Direct Methods of Detecting Exoplanets Specialized optics and observation methods have made some exoplanet images possible. These images from the Palomar Observatory in California show an array of planets around the star HR 8799. The light from the central star is blackened to reveal its planets.

14. The Search for Another Earth Kepler’s Results This diagram shows locations of Kepler planet candidates in the Kepler full field image. The number of candidates in Kepler data now totals 4,696 potential planets orbiting 4,743 stars. There are 1935 confirmed planets as of January 2016. The Kepler Mission assesses each candidate with its "Follow-up Observing Program" designed to distinguish true planets from the imposters.

15. The Search for Another Earth Orrery of Planet Candidates A visualization of all the multiple- planet systems discovered by the Kepler spacecraft as of February 2012. The orbit radii are to scale with respect to each other and planet sizes are to scale with respect to each other, but orbits and planet sizes are different scales. The colors are in order of semi- major axis: two-planet systems (242 in all) have a yellow outer planet; 3-planet (85) green, 4- planet (25) light blue, 5-planet (8) dark blue, 6-planet (1, Kepler-11) purple.

16. The Search for Another Earth TheHabitable Zone Kepler is seeking evidence of Earth-size planets in the habitable zone of Sun-like stars. The bigger challenge is to find planets in the habitable zone of their stars where liquid water and possibly life might exist. To date, Kepler has confirmed 297 planet candidates in the habitable zone. It appears that some of these planets have water present.

17. The Search for Another Earth TheHabitable Zone Kepler is seeking evidence of Earth-size planets in the habitable zone of Sun-like stars. The bigger challenge is to find planets in the habitable zone of their stars where liquid water and possibly life might exist. To date, Kepler has confirmed 297 planet candidates in the habitable zone. It appears that some of these planets have water present.

18. The Search for Another Earth What’s Next for Kepler? The loss of two reaction wheels on the Kepler spacecraft in 2013 brought an end to Kepler's primary mission. In June 2014, the K2 mission was established which enables continued observations with Kepler. K2 is a community-driven mission which entails observing “campaigns” of fields distributed around the ecliptic plane. Kepler is expected to continue operating until 2017 or 2018.

19. The Search for Another Earth GAIA Spacecraft Continued and Future Research Spacecraft Operations into the future: --Continued operation of Kepler, Hubble and Spitzer Space Telescopes --Operation by ESA’s Gaia satellite --Launch of ESA’s CHaracterizing ExOPlanet Satellite (CHEOPS) --Launch of NASA’s Transiting Exoplanet Survey Satellite in 2017 --Launch of NASA’s James Webb Space Telescope in 2018.

20. The Search for Another Earth For more information regarding the search for exoplanets NASA Planet Quest: The Search for Another Earth http://planetquest.jpl.nasa.gov/ NASA Exoplanet Exploration Program http://exep.jpl.nasa.gov/ Exoplanet Science Institute http://nexsci.caltech.edu/ ESA Gaia http://www.esa.int/Our_Activities/Space_Science/Gaia

21. The Search for Another Earth