The Search for Exoplanets and Earths Outside our Solar System

Transcription

1 The Search for Exoplanets and Earths Outside our Solar System Dr. Damian J. Christian Cal State University Northridge

2 The Search for Planets around I. Quick notes on our Solar System & Planet Formation II. Methods for finding exoplanets III. Transit Detection and SuperWASP (Wide Angle Search for Planets) IV. Characterizing Exoplanets V. Habitable Zone & Search for Earths VI. Summary Nearby Stars.

3 Part I. Our Solar System &Planet Formation. Two leading theories: Core Accretion vs Gravitational Instability But first review properties of our Solar System

4 Our Solar System Rocky planets, Gas Giants & Ice Giants plus smaller objects

5 Planetary Orbits Mercury Venus Earth All planets in almost circular (elliptical) orbits around the sun, in approx. the same plane (ecliptic). Sense of revolution: counter-clockwise Sense of rotation: counterclockwise (with exception of Venus, Uranus, and Pluto) Orbits generally inclined by no more than 3.4 o Exceptions: Mercury (7 o ) Pluto (17.2 o ) (Distances and times reproduced to scale)

6 Solar System Facts Observed: Planets orbit Sun in the Same Plane Generally rotation and revolution in same direction (except Venus, Uranus and Pluto). Differentiation: higher densities in inner solar system, lower density planets in outer solar system Debris (asteroids, comets, Kuiper Belt objects etc)., Age measurements (Earth, Moon, Meteorites) all about 4.6 Gyr Terrestrial Small High density Low mass Great moons not common Jovian Large Low Density High Mass Great & many moons common Rings common

7 Formation and Growth of Planetesimals Planet formation starts with clumping together of grains of solid matter: Planetesimals Planetesimal growth through condensation and accretion. Planetesimals (few cm to km in size) collide to form planets. Gravitational instabilities may have helped in the growth of planetesimals into protoplanets.

8 The Story of Planet Building Planets formed from the same protostellar material as the sun, still found in the Sun s atmosphere. Rocky planet material formed from clumping together of dust grains in the protostellar cloud. Mass of less than ~ 15 Earth masses: Planets can not grow by gravitational collapse Earthlike planets Mass of more than ~ 15 Earth masses: Planets can grow by gravitationally attracting material from the protostellar cloud Jovian planets (gas giants)

9 Define a Planet Planets are defined to be less then 13 Jupiter Masses (M J ) Above 80 Jupiter Masses an object can fuse Hydrogen into Helium and become a star (recall this is 8% the mass of the Sun!) Objects below 80 M J are called Brown Dwarfs M < 13 M J Planet 13 < M < 80 M J Brown Dwarfs M > 80 M J Small Star

10 Part II. Methods for finding Exoplanets.

11 II. Methods for Finding Extra Solar Planets Pulsar Timing: Pulsars' signals are extremely regular (spinning neutron star) Small anomalies in the timing of pulsars can betray the Planets with masses on order of the Earth's or greater can be detected. First earth-mass extra-solar planets were confirmed in 1992 Astrometry wobble on the sky Gravitational Lensing enhance starlight Direct Imaging Radial Velocities Photometric Transits

12 Methods for Finding Extra Solar Planets Pulsar Timing: Pulsars' signals are extremely regular Small anomalies in the timing of pulsars can betray the Planets with masses on order of the Earth's or greater can be detected. First earth-mass extra-solar planets were confirmed in 1992 Astrometry wobble on the sky Gravitational Lensing enhance starlight Direct Imaging Radial Velocities Photometric Transits

13 General Relativity This bending of light by the gravitation of massive bodies has indeed been observed: During total solar eclipses: The positions of stars apparently close to the sun are shifted away from the position of the sun. New description of gravity as curvature of space-time!

14 Now add a planet:

15 Methods for Finding Extra Solar Planets Pulsar Timing: Pulsars' signals are extremely regular Small anomalies in the timing of pulsars can betray the Planets with masses on order of the Earth's or greater can be detected. First earth-mass extra-solar planets were confirmed in 1992 Astrometry wobble on the sky Gravitational Lensing enhance starlight Direct Imaging Radial Velocities Photometric Transits

16 Direct Imaging Contrast between the Planets and the Sun ~10 9 ~10 6

17 Methods for Finding Extra Solar Planets Direct Imaging Examples HR 8799 est 7-10 Jupiter Masses b - dist == 68 AU; P = 470 yrs c - dist = 38 AU; P = 189 yrs d - dist = 24 AU; P = 100 yrs

18 Methods for Finding Extra Solar Planets Pulsar Timing: Pulsars' signals are extremely regular Small anomalies in the timing of pulsars can betray the Planets with masses on order of the Earth's or greater can be detected. First earth-mass extra-solar planets were confirmed in 1992 Astrometry wobble on the sky Gravitational Lensing enhance starlight Direct Imaging Radial Velocities Photometric Transits

19 The Doppler Effect = c/l Sound waves always travel at the speed of sound just like light always travels at the speed of light, independent of the speed of the source of sound or light. Blue Shift - shorter wavelength (higher frequencies) v r Red Shift - longer wavelength (lower frequencies) The light of a moving source is blue/red shifted by Dl/l o = l-l o /l o = v r /c l o = actual wavelength emitted by the source Dl = Wavelength change due to Doppler effect v r = radial velocity

20 Radial Velocities We do NOT see the planet, only the shift in the Star s absorption lines -- the amplitude of these depends on the Planets MASS! Doppler Effect => M p V p = M * V * QuickTime and a Sorenson Video 3 decompressor are needed to see this picture.

21 Doppler Effect Radial Velocities

22 Methods for Finding Extra Solar Planets Pulsar Timing: Pulsars' signals are extremely regular Small anomalies in the timing of pulsars can betray the Planets with masses on order of the Earth's or greater can be detected. First earth-mass extra-solar planets were confirmed in 1992 Astrometry wobble on the sky Gravitational Lensing enhance starlight Direct Imaging Radial Velocities Photometric Transits

23 Photometric Transit Detection QuickTime and a YUV420 codec decompressor are needed to see this picture. ~1% ~ 2-3 hrs

24 First Transits of Extra-Solar Planets P=3 days and distance 0.04 AU Hot-Jupiters First transit detected by Charbonneau et al (1999): HD209458b

25 Current ESP 861 planets around 677 stars About 20% of ESP are Hot-Jupiters (1/20th Earth-Sun distance, P< 4 days!) 128 multiple systems Only a few Solar System Analogs

26 Stop: Define Types of Stars O B A F G K M Some Quick Facts: * A - stars H lines the strongest * Sun is a G star * O Stars: H all ionized - no lines! * B/A stars not enough absorption lines to do Doppler Method!

27 Part III. More Details on the Transit Detection and SuperWASP (Wide Angle Search for Planets).

28 Photometric Transit Detection (Why?) Primary Questions: What are their sizes and masses? What are Hot-Jupiters made of? How often do Hot-Jupiters form? How do they form? Are there habitable planets? Earth-sized planets detectable from space COROT and NASA s Kepler Ground based astronomy only sensitive to Hot-Jupiters/Saturns Technique: Need to Monitor 1000 s of stars!

29 Wide Field Observations of Comets Don Pollacco - SuperWASP PI - lets look for transiting planets by Monitoring 1000 s of stars. Comet Hyakutake 1996B2 EEV1280x2220 thick detector read out within observatory infra-structure Usable FOV 30x40 degrees! Nightmare! Upgrade of detector to 2048x2048 SITe2 chip FOV 10x10 degrees, little vignetting

30 WASP0: Technology Demonstrator Wide Angle Search for Planets prototype camera, total cost about 15K produced >1GB/night Everything commercially available, e.g. detector Apogee 2048x bit. Operated for 3 months in La Palma and 6 months+ in Greece (2000) Funded between Queen s University Belfast / STFC

31 SuperWASP I La Palma Use COTS - keep cost down Enclosure w/ sliding roof Weather station, GPS system, air-conditioning Telescope control PC (Linux) 1 PC per camera Data Storage (2 TB RAID/DLT) 8 camera set-up: Telescope mount: Rapid slewing (10 o /sec) Pointing to ~few arcsec

32 SuperWASP II South Africa

33 Ultra-Wide Field: Sample Image WHT Wide-Field Survey: 0.09 deg 2 4 deg 2 Surprisingly, wide field astronomy is relatively new! 4 Camera Image of Orion (M42) (1 sec exposure). 15 o D. Christian (QUB) SuperWASP 8 x 61deg 2

34 Ultra-Wide Field: Sample Image 5 Camera Image of Galactic Center 15 o full moons

35 ESP Survey fields Observations started 16 th April 2004 Overlapping fields at Dec=+28 Avoid crowding of Galactic Plane 30sec exposure time+20 sec overhead 8 fields per scan ~8 minute cadence Image ~3000 sq. deg each night (~7% of sky) Imaged more than 50 million stars to date

36 Images to light curves X X X Factors leading to detection Orbital inclination ~10% should transit Depth of transit ~ (R p /R * ) 2 Deeper transits for later-type stars Early estimates: 1 to 10 planets per 25,000 stars

37 Sample ESP Light Curves Light curve First Planet; WASP-1 Folded light curve (P ~ 11 d)

38 But wait: Nature is Tricky: Many other stars can look like a planet transit: False Positives Grazing Eclipsing binaries Foreground binary diluted by faint background star Secondary is really a brown dwarf!

39 False Positives Grazing Eclipsing binaries Foreground Binary diluted by faint background star Secondary is really brown dwarf Background star

40 False Positives Grazing Eclipsing binaries Foreground Binary diluted by faint background star Secondary is really brown dwarf

41 Eliminating False Positives Grazing Eclipsing binaries -moderate resolution spectroscopy Foreground Binary diluted by faint background star -Deeper Imaging ~1m telescope Secondary is really brown dwarf -Weigh System with Radial Velocities

42 Planet Confirmation Weigh System with Radial Velocities Measure Radial Velocities to ~ few m/s Star towards us -- blue-shifted Star away from us -- red shifted Note: really measure M p sini

43 Planet Confirmation: Transit profiles and Radial Velocity orbits WASP-1 & WASP-2 first planets discovered 2006! Collier Cameron et al 2007

44 SuperWASP Planets: WASP 1 to 15!!! There are >90 SuperWASP planets now (60+ published!)

45 Part IV. Characterizing Exoplanets.

46 The Planet s Atmosphere Characterize an exoplanet s atmosphere: Transmission Spectroscopy Star Planet Spectra during primary eclipse: Chemical composition, scattering properties Atmosphere

47 What s in their atmospheres? Atmospheric composition may be similar to cool browndwarf stars with T eff ~ 1000K Optical spectra dominated by alkali-metal absorption? Silicate cloud decks? Silhouette of planet during transit should appear larger in strong absorption lines of alkali metals: Line photons blocked high in atmosphere Continuum photons blocked by clouds Opaque silicate cloud deck Extended atmosphere With gaseous Na, K, H 2 O, CH 4,...

48 Extended Lyman a silhouette Vidal-Madjar et al (2003) Nature 422, 123

49 Are Hot-Jupiters disappearing!? Heating of the star on the Hot-Jupiter s atmosphere may cause it to evaporate. Deadly Tides Mean Early Exit for Hot Jupiters

50 We can measure the decrease in light when the planet is eclipsed by the a star and build a temperature profile as a function of orbital phase Spitzer IR imaging - secondary eclipse Planet behind star - depth 7 times smaller!

51 IR Temperature of an Extra Solar Planet

52 Part V. Habitable Zone & The Search for Earths.

53 Exoplanet detections limits Search for super-earths a few to 10 x M E

54 Searching for life Searching for life as we know it: The 1 st step is to find a rocky planet in the stellar habitable zone (HZ) - can have liquid water, although it could also be a satellite of a gas giant. The planet should be in the Galactic habitable zone, not in a globular cluster or close to the Galactic center. The planet should not be tidally locked, ruling out most late-type stars. The system should not be young, so that there are not too many catastrophic comet/asteroid impacts. Find an atmosphere that shows out of equilibrium composition, containing known biomarkers. Refernce: Dante Minniti (U. Católica)

55 Terrestrial planets the Holy grail April 2007: - Discovery of 5M E (minimum mass) planet around M3 dwarf star 20 light years away: Gliese 581c - Orbits star in 13 days - Resides in warm edge of Habitable zone - Computer models suggest rocky or ocean world continuously habitable zone (or CHZ) - liquid water for main sequence lifetime

56 Press gets very excited about Habitable exoplanets!

57 New!! Space Satellites to find Earth-sized transiting planets: CoRot and Kepler Kepler: launched March 2009: 3.5+ yr mission to find Earthlike planets

58 Kepler MISSION CONCEPT Kepler Mission is optimized for finding habitable planets ( 0.5 to 10 M ) 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 => 4s detection for Earth-size transit Mission: Heliocentric orbit for continuous viewing > 3.5 year duration 58

59 Kepler SPACECRAFT 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 Primary Mirror 1.4 m dia., 85% lt. wt. Fully assembled Kepler photometer Mounted on the spacecraft Spacecraft bus integration 59

60 FIELD OF VIEW IN CYGNUS 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) 60

61 Sample Kepler ESP Kepler-11 - new 6 planet system!

62 Kepler 10 = Earth-sized planet 4.5M E and 1.4 R E

63 New Kepler ESP Kepler-22b - planet in HZ size 2.4 R Earth P ~ 290 days 0.85 AU

64 Kepler-16 = orbits a binary star

65 Kepler 37b - smallest yet (Feb 2013) Kepler LY distant 3 planets 13 days - b R Earth 21 days - c days - d

66 Using Kepler data, researchers estimate that six percent of red dwarf stars in the galaxy have Earth-size planets in the "habitable zone,"

67 Searching for life Infrared Spectra: The Ozone test Reference: Dante Minniti (U. Católica)

68 FUTURE MISSIONS TESS: Searching Closer to Home The Transiting Exoplanet Survey Satellite is being designed to search for the most promising exoplanet targets for nextgeneration studies.

69 Summary & The Future Over 670 planets systems known - Kepler with quadruple this Mostly discovered with indirect methods Improved imaging/rv promises smaller ESP detections Future space missions for discovery and characterization > 90 extra-solar planets from SuperWASP - from transits» FUTURE: New ESP Candidates from season Require spectroscopic follow-up Exciting prospect to measure planet's atmosphere with Hubble/Spitzer Space Telescopes Earth-size planets now!! CoRoT & Kepler Ton a public Kepler data to analyze! Further our understanding on how planets form Search for Life in the Galaxy

70 Questions?

71 Size Relative to Earth Planet Candidates as of June 2010 Jun 2010 Orbital Period in days

72 Size Relative to Earth Planet Candidates as of Feb 2011 Jun 2010 Feb 2011 Orbital Period in days

73 Size Relative to Earth Planet Candidates as of Dec 2011 Jun 2010 Feb 2011 Dec 2011 Orbital Period in days

74 Sizes of Planet Candidates 1181 (+78%) Neptune-size Super Earth-size 680 (+136%) Earth-size 207 (+204%) 203 (+23%) Jupiter-size 27 (+42%) Super Jupiter-size

75 & Exoplanet Materials on-line

76 Earthshine spectrum The Moon as seen from the Earth. The Earth as seen from the Moon (only18% land). Eathshine + scattered moonlight before substraction Woolf et al. (2002), Arnold et al. (2002) EXTRASOLAR PLANETS ESO October 2005 Dante Minniti (U. Católica)

77 A Census of the Stars (2) Faint, red dwarfs (low mass) are the most common stars. Bright, hot, blue main-sequence stars (highmass) are very rare. Giants and supergiants are extremely rare.

78 Masses of Stars in the Hertzsprung- Russell Diagram = Star s Lifetime The higher a star s mass, the brighter it is: L ~ M 3.5 High-mass stars have much shorter lives than low-mass stars: 40 M sun : ~ 1 million yr!!! t life ~ M -2.5 Sun: ~ 10 billion yr. 15 M sun : ~ 11 million yr. 0.1 M sun : ~ 3 trillion yr. Only way to get masses of stars: Weigh them in binaries!!