JOHANNES KEPLER A Search for Habitable Planets By

JOHANNES KEPLER A Search for Habitable Planets ( By permission Sternwarte Kremsmünster) A guy who thought a lot about planets

A Search for Habitable Planets Kepler Mission A SEARCH FOR HABITABLE PLANETS Nancy Schaff Cornell University Dept. of Astronomy Center for Radiophysics & Space Research Adapted from a presentation by David Koch NASA Ames Research Center

OVERVIEW A Search for Habitable Planets • What makes for a Habitable Planet • Different Methods for Finding Planets • Planets Discovered to Date • Transit Photometry • Kepler Mission

A Fundamental NASA Mission Goal: A Search for Habitable Planets – To place our Solar System in context with other planetary systems – To provide data on possible platforms for astrobiology beyond our Solar System • Does life in any form however simple or complex, carbon-based or other, exist elsewhere than on Earth? • Are there Earth-like planets beyond our solar system? These goals imply study of terrestrial planets in the habitable zones of solar-type (or smaller) stars…

WHAT DOES HABITABLE MEAN TO YOU? A Search for Habitable Planets • Right temperature • Air • Liquid water • Light to keep you warm and to see • Radiation shield • Meteor (asteroid/comet) protection

THINGS THAT AFFECT TEMPERATURE Looking for a temperature that makes liquid water on the surface of the planet possible… Factors that define the Habitable Zone (HZ) for a star: 1. Temperature of star 2. Distance from the star 3. Shape of planet’s orbit: how elliptical 4. Planet’s atmosphere: greenhouse gases A Search for Habitable Planets

PLANET TEMPERATURE AFFECTS HABITABILITY aka “Goldilocks zone” A Search for Habitable Planets

THE HABITABLE ZONE FOR VARIOUS STELLAR TYPES A Search for Habitable Planets The Habitable Zone (HZ) in green is the distance from a star where liquid water is expected to exist on the planets surface.

WHAT IS IMPORTANT ABOUT AN ATMOSPHERE? A Search for Habitable Planets • Composition (Earth) free oxygen (about 21%) mostly inert (about 78% nitrogen) very little toxic gases • Composition affects temperature Minimize day-night extremes Greenhouse gases (water, CO 2) hold in the heat • Acts as an invisible protective shield Cosmic rays (high energy gamma-rays, protons, electrons) Solar wind and solar flares (charged particles) UV - ultraviolet Micrometeoroids (e. g. , puts holes in Space Shuttle window) • Transports water Rain

PLANET SIZE AFFECTS HABITABILITY A Search for Habitable Planets • Planets form by accretion from a disk of gas and dust • Too small (about <0. 5 ME): Can’t hold onto a life sustaining atmosphere (Mercury, Mars) • Too big (about >10 ME): Can hold onto the very abundant light gases (H 2 and He) and turn into a gas giant (Jupiter, Saturn, Uranus, Neptune) Copyright Lynnette Cook

KEY POINTS THAT GUIDE THE SEARCH A Search for Habitable Planets 1. Stellar type => Which stars to search 2. HZ => Orbital periods and how long to look 3. Planet sizes => Sensitivity or precision needed

A Search for Habitable Planets DETECTING EXTRA-SOLAR PLANETS (aka Exoplanets) That is, Planets orbiting other stars

TECHNIQUES FOR FINDING EXTRASOLAR PLANETS A Search for Habitable Planets Method Mass Limit Status Pulsar Timing Lunar Successful (4) Radial Velocity super-Earth Successful (300+) sub-Jupiter super-Earth In development Under study sub-Jupiter Earth Successful (20+) numerous groups HST, Co. Ro. T Kepler Astrometry Ground Space Transit Photometry Ground Space Reflection Photometry Space Microlensing Ground Direct Imaging Space sub-Jupiter Kepler super-Earth OGLE (4) Earth Under study t=period, a=semi-major axis, mp=planet mass, Ap=planet area, I=orbit inclination, e=eccentricity, Ds=distance to star (Source: J. Lissauer)

EXTRA-SOLAR PLANET DETECTIONS A Search for Habitable Planets N. B. 430 exoplanets as of April 15, 2010 Note: Masses are only lower limits except for transit cases and typically about 2 x greater than shown

DISCOVERY OF EXTRASOLAR PLANETS A Search for Habitable Planets The “wobble” method gets the orbital period, semi-major axis, and a lower limit on the mass of the planet. This has detected down to 7 Earth-mass planets very close in, (but favors gas giant planets).

WE NEED A DIFFERENT APPROACH A Search for Habitable Planets • Earth-like planets are about 300 times less massive and about 100 times smaller in area than Jupiter • Radial velocity (Doppler spectroscopy) method unable to detect Earth-size planets • Need a different approach that can detect smaller planets • No method exists for detecting habitable planets from ground-based observatories • The Kepler Mission uses photometry to detect transits and can detect Earth-size planets from space • The Kepler Mission is optimized to detect habitable planets in the habitable zone of solarlike stars Exoplanet encyclopedia http: //exoplanet. eu

Detecting Planets by Photometry A Search for Habitable Planets HD 209458

USING PHOTOMETRY TO DETECT EARTH-SIZE PLANETS • A Search for Habitable Planets The relative change in brightness (DL/L) is equal to the relative areas (Aplanet/Astar) Mercury Transit 2006 Jupiter: 1% area of the Sun (1/100) Earth or Venus 0. 01% area of the Sun (1/10, 000) • To measure 0. 01% must get above the Earth’s atmosphere • Method is robust but you must be patient: Require at least 3 transits preferably 4 with same brightness change, duration and temporal separation

Kepler MISSION CONCEPT A Search for Habitable Planets • Kepler Mission is optimized for finding habitable planets ( 0. 5 to 10 MÅ ) in the HZ ( near 1 AU ) of solar-like stars • Continuously and simultaneously monitor 100, 000 main-sequence stars • Use a one-meter Schmidt telescope: FOV >100 deg 2 with an array of 42 CCD • Photometric precision: Noise < 20 ppm in 6. 5 hours V = 12 solar-like star => 4 s detection for Earth-size transit • Mission: Heliocentric orbit for continuous viewing > 3. 5 year duration

Kepler PHOTOMETER A Search for Habitable Planets Photometer = CCD sensors+ Telescope Kepler will be 9 th largest Schmidt ever built and the largest telescope launched beyond earth-orbit The Kepler photometer is a simple single purpose instrument • Schmidt telescope design with a 0. 95 meter aperture and about 12 degree diameter field-ofview • Pointed at and records data from a single group of stars for the four year duration of the mission

Kepler Focal Plane A Search for Habitable Planets The photometer is composed of just one "instrument, " which is, an array of 42 CCDs (charge coupled devices). Each 50 x 25 mm CCD has 2200 x 1024 pixels. The CCDs are not used to take pictures. The images are intentionally defocused to improve the photometric precision.

Kepler SPACECRAFT A Search for Habitable Planets Schmidt Corrector 0. 95 m dia. Sunshade Spider with Focal Plane and Local Detector Electronics Upper Telescope Housing Focal Plane 95 Mega pixels, 42 CCDs Lower Telescope Housing Fully assembled Kepler photometer Mounted on the spacecraft Primary Mirror 1. 4 m dia. , 85% lt. wt. Spacecraft bus integration

FIELD OF VIEW IN CYGNUS A Search for Habitable Planets The Kepler star field is a part of the extended solar neighborhood in the Cygnus-Lyra regions along the Orion arm. It is located on one side of the summer triangle (Deneb-Vega-Altair)

SEARCHING THE EXTENDED SOLAR NEIGHBORHOOD A Search for Habitable Planets The stars sampled are similar to the immediate solar neighborhood. The stars actually come from all over the Galaxy near our radius, since they wander after being born. Young stellar clusters and their ionized nebular regions highlight the arms of the Galaxy.

EARLY RESULTS A Search for Habitable Planets Results announced January 4, 2010 from first six weeks of data collection after science operations commenced on May 12, 2009 • Known as "hot Jupiters" because of their high masses and extreme temperatures • Range in size from similar to Neptune to larger than Jupiter • Orbits ranging from 3. 3 to 4. 9 days • Estimated temperatures range from 2, 200 to 3, 000 degrees F, hotter than molten lava and much too hot for life as we know it • All five of the exoplanets orbit stars hotter and larger than Earth's sun.

SUMMARY A Search for Habitable Planets The Kepler Mission will: Observe more than 100, 000 dwarf stars continuously for 3. 5 to 6+ years with a precision capable of detecting Earth’s in the HZ The Kepler Mission can discover: Planet sizes from that of Mars to greater than Jupiter Orbital periods from days up to two years About 600 terrestrial planetary systems if most have 1 AU orbits About 1000 inner-orbit giant planets based on already known frequency A NULL result would also be very significant ! ! ! Results on giants expected 9 months after launch (March 2009) and will continue for 3. 5 to 6+ years http: //kepler. nasa. gov 29

Human Orrery A Search for Habitable Planets

A Search for Habitable Planets Introductory questions for Detecting Extrasolar Planets from Space Science Sequence Grades 6 -8 Unit 4 Great Explorations in Math and Science (GEMS) http: //www. lhsgems. org

A Search for Habitable Planets Do you think there are planets orbiting other stars? . . . How many?

A Search for Habitable Planets Are all stars the same size and temperature as the Sun?

A Search for Habitable Planets How might the type of star affect whether it has habitable planets?

A Search for Habitable Planets If there is a certain zone around a star where life might exist, what must be critical qualities of that zone?

A Search for Habitable Planets What things would you want to know about a newly discovered planet? Back to slide 14

A Search for Habitable Planets Why would exoplanets be hard to detect? What methods do astronomers use to find planets?

WHAT’S THIS? A Search for Habitable Planets

A Search for Habitable Planets What happens when a planet transits a star? Make a model that you can use to demonstrate a planet transit.

TRANSIT MODEL DESIGN ACTIVITY For each team of 4– 6 students: • 1 snake book light • 1 prepared Ping-Pong ball (see Getting Ready) • several round, opaque plastic beads (ranging in size from 8 mm to 16 mm in diameter) • 2 or more pipe cleaners • 1 or 2 chopsticks or thin wooden dowels • black thread • 4" x 6” index cards • tape • paper or plastic bag to hold the materials A Search for Habitable Planets Create a model “star” by setting up a light bulb and socket in the middle of the classroom for teams to demonstrate their transits.

A Search for Habitable Planets What kind of orbit would allow us to see a transit? Ball-on-stick demo

A Search for Habitable Planets What’s wrong with this statement: “If a star has an orbiting planet, astronomers can usually detect it by transit observations”

A Search for Habitable Planets Kepler is designed to monitor brightness of 100, 000 stars simultaneously for over 3 years.

A Search for Habitable Planets Scale of the model? Return to questions about planets (slide 6) • Are there more questions? • Do transit observations help us answer the questions?

DEMO LEGO MODEL A Search for Habitable Planets

A Search for Habitable Planets Transit Tracks trial investigation from Full Option Science System (FOSS) Planetary Science course

A Search for Habitable Planets BRIGHTNESS Imagine you have a light sensor aimed at the star. What would the transit of a book like if you made a graph of light intensity vs time? TIME

A Search for Habitable Planets BRIGHTNESS What would the transit of a planet look like if you made a graph of light intensity vs time? TIME

The graph is a “light curve” A Search for Habitable Planets It can lead to finding: - The SIZE of the planet (based on brightness change and size of star) - ORBITAL PERIOD of the planet – time between transits - ORBITAL SIZE – distance from star (from mass of star and orbital period, using Kepler’s 3 rd Law) - TEMPERATURE of planet (from planet’s distance and temperature of star) Why would those characteristics be important?

A Search for Habitable Planets How does a planet’s size and orbit affect the transit?

A Search for Habitable Planets Is there a relationship between the planet’s period and how far it is from the star? Kepler’s Third Law: the square of the period (in years) equals the cube of the semi-major axis of orbit (in AUs) P 2 = a 3

A Search for Habitable Planets

A Search for Habitable Planets

A Search for Habitable Planets