The Search for Habitable Worlds

1. G. Chin (GSFC) The Search for Habitable Worlds How Would We Know One If We Saw One? Dr. Victoria Meadows NASA Astrobiology Institute Jet Propulsion Laboratory/California Institute of Technology

2. What Is Astrobiology? • Astrobiology is the scientific study of life in the universe, its past, present and future. • Astrobiology seeks to answer three questions: • How does life begin and develop? • Does life exist elsewhere in the universe? • What is life’s future on Earth and beyond? • Astrobiology is an interdisciplinary science • combines biology, chemistry, geology, astronomy, planetary science, paleontology, oceanography, physics, and mathematics to answer these questions.

3. 109 106 The Search for Planets Around Other Stars

4. Where would we start the search for life outside our Solar System? First, find a habitable world

5. The Search for Planets Around Other Stars There are many challenges to observing extrasolar planets • in the visible, they don’t give off their own light • they are VERY far away, which makes them very faint • They are lost in the glare of their star

6. Indirect Detection of Extrasolar Planets These techniques use changes in the position or brightness of a star to infer the existence of a planet

7. The Doppler Technique http://planetquest.jpl.nasa.gov

8. Astrometry

9. Transit

10. Microlensing 

11. Suitable Parent Stars • To be a suitable “parent” a star must • live long enough • stars 1.5M (O,B,A) age too quickly • Be bright enough so that the planet doesn’t have to be too close • stars 0.5M (M) will tidally lock • Be “stable” • Favor stars with high “metallicity” • Special constraints on a binary system • Therefore we search for planets around F, G and K stars (yellow to orange)

12. A Multitude of Worlds 116 • 107 Planets • 93 Planetary Systems • 12 Multiple Star Systems Not bad for not being able to see anything! But there’s one problem...

13. Too Big! • These planets are “giant planets” • smallest found so far is about the size of Neptune (0.1 MJ) • 12% of stars surveyed have giant planets • Small, rocky, Earth-like terrestrial planets around “friendly” stars still elude us R. Hasler

14. Kepler Launch 2007 T. Brown and D. Charbonneau The Kepler Mission Measures stellar brightness changes lasting for 2-16 hours caused by transiting terrestrial planets. Monitoring 100,000 stars for 4 years! • Transit gives planet size and orbital period Transit Telescope

15. The Space Interferometry Mission • Launch in 2009 • Optical interferometry • Astrometry 100x more accurate (1-2µ arcseconds) • Search for planets > 1 M around the few nearest stars, and 5-10 M planets around stars within 10pc. • Technology demonstration for spacebourne interferometry.

16. Direct Detection of Extrasolar Planets

17. Uses multiple mirrors to simulate the angular resolution of a much larger telescope. Two architectures “free-flyer” in precision formation fixed structure (“TPF on a stick”). Uses destructive interference to place the star in a “null”, reducing its light by a factor of a million Infrared Nulling Interferometer

18. A coronagraph blocks the light from a bright object so that fainter nearby things can be seen. Implemented on large optical telescope. The coronagraph must minimize both the direct light from the star, and minimize the telescope diffraction pattern to maximize angular resolution. Current designs use “masks” to simulate a telescope of a different configuration to preferentially scatter light in a restricted area on the focal plane. Visible Light Coronagraph

19. Terrestrial Planet Finders Terrestrial Planet Finder NASA Direct detection of planets Launch 2011-2015 Darwin ESA

20. What Is a Habitable World? A world that can maintain liquid water on its surface

21. What Makes a Habitable World? • Location, Location, Location • Planet Mass: Atmospheric mass and plate tectonics • Atmospheric Composition: reflectivity and climate balance • Circular(ish) Orbits

22. Modern Proterozoic Archean The Family of Earths 1. Modern day Earth is only one of the “habitable Earths” 2. A habitable world does not require high levels of atmospheric oxygen.

23. The Instantaneous Habitable Zone “The region around a star in which an Earth-like planet could maintain liquid water at some instant in time” (0.93-1.37AU for our Solar System) H2O CO2 Image courtesy of J.F.Kasting. After Kasting, Whitmire and Reynolds, 1993.

24. The Continuously Habitable Zone • The region in which a planet could remain habitable for some specified period of time • Our Solar System has had a CHZ spanning 0.95-1.15AU in the past 4.6 Gy. • The Sun may become 10% brighter in the next 1.1 Gy, so earth may be too hot in another 500-900My! Image courtesy of J.F.Kasting.

26. Learning About Distant Worlds Radio Infrared Visible Ultra- Violet X-Ray

27. How Can We Tell If A Planet is Habitable? jj • “Environmental” Characteristics • parent star, placement in solar system, other planets • “Photometric” Characteristics • brightness, color, how it varies over time

28. Gauging the Greenhouse Planetary Energy balance is given by: σTe4 = S(1-A)/4 The effective radiating temperature Te denotes the average temperature of the emitting layer Δ 37 C Δ 520 C A planet’s greenhouse effect is at least as important in determining that planet’s surface temperature as is its distance from the star! After Table 9.1, Bennet, Shostak, Jakosky, 2003

29. crisp

30. Net 60 Stratopause 50 Emission 40 Ozone Absorption 30 20 Tropopause 10 Absorption Water Vapor 0 200 250 300 Remote-Sensing In the visible, sunlight is reflected and scattered back to the observer, and is absorbed by materials on the planet’s surface and in its atmosphere. O3 The planet is warm and gives off its own infrared radiation. As this radiation escapes to space, materials in the atmosphere absorb it and produce spectral features.

31. H2O N2O CH4 The Earth From Space in the Infrared O3 CO2

32. The Earth From Space In The Visible Crisp, Meadows

33. Viewing Angle Differences Phase and Seasonal Variations

34. Hi! How can we tell if a planet is inhabited? DEAFENING SILENCE! Without direct contact with an alien civilization, or travelling to the nearest solar system, our best chance for finding life in the Universe is to look for global changes in the atmosphere and surface of a terrestrial planet.

35. The Signs of Life CH4 O3 Life Changes a Planet’s Atmosphere

36. Life Changes a Planet’s Surface

37. Life Changes a Planet’s Appearance Over Time Gas or surface signatures that change with day-night, or seasons

38. What a planet looks like from space depends on many things…..

42. Observer Synthetic Spectra Atmospheric and surface optical properties Radiative Transfer Model Task 1: Spectra Task 2: The Climate Model (SMARTMOD) Stellar Spectra Radiative Fluxes and Heating Rates Atmospheric Thermal Structure and Composition Task 3: The Coupled Climate-Chemistry Model Climate Model UV Flux and Atmospheric Temperature Atmospheric Composition Task 4: The Abiotic Planet Model Atmospheric Chemistry Model Atmospheric Thermal Structure and Composition Atmospheric Escape, Meteorites, Volcanism, Weathering products Task 5: The Inhabited Planet Model Virtual Planetary Laboratory Exogenic Model Geological Model Atmospheric Thermal Structure and Composition Biological Effluents Biology Model The Virtual Planetary Laboratory

43. VPL TEAM MEMBERS NAME INSTITUTION CONTRIBUTION Dr. Victoria Meadows* JPL /SSC PI: radiative transfer/astronomical observing Dr. Mark Allen* JPL/Caltech chemical models Dr. Linda Brown* JPL laboratory spectroscopy Dr. Rebecca Butler JPL spectroscopic database Dr. David Crisp* JPL radiative transfer modeling Dr. Chris Parkinson JPL/Caltech upper atmosphere modeling Dr. Giovanna Tinetti JPL/USC/NRC planetary models, effect of orbit Dr. Thangasamy Velusamy* JPL astronomical instrumentation models Dr. Mark Richardson* Caltech global models, upper atmosphere boundary Dr. Ian McKewan Caltech parallelization algorithms, model interfacing Prof. Yuk Yung* Caltech chemical models Dr. Wesley Huntress, Jr* CIW geophysical laboratory data Prof. James Kasting * Penn. State climate modeling, escape processes Ms. Kara Krelove Penn. State->Arizona climate modeling Mr. Pushker Karecha Penn. State Archean ecosystems Dr. Antigona Segura Penn. State astrophysics, climate modeling Ms Irene Schneider Penn. State geosciences Mr Shawn Goldman Penn. State radiation and biology Prof. Norm Sleep* Stanford geology, geochemical cycles Dr. Martin Cohen* UC, Berkeley stellar spectra Dr. Robert Rye* USC microbiology, parameterization of life Dr. David DesMarais* NASA Ames microbiology Dr. Kevin Zahnle* NASA Ames impact processes, chemical models Dr. Francis Nimmo The Royal Society plate tectonics, geochemical cycles Dr. Monika Kress U. Washington solar system architectures, volatile delivery Prof. Janet Seifert Rice University biochemistry, ancient metabolisms Dr. Nancy Kiang GISS biometeorology, leaf structure Dr. John Armstrong Weber University climate studies, earth systems Dr. Cherilynn Morrow* Space Science Institute education and public outreach Dr. Jamie Harold Space Science Institute education and public outreach Dr. Ray Wolstencroft Royal Observatory Edinburgh polarization, chlorophyll signatures Dr. Jeremy Bailey Australian Centre for Astrobiology terrestrial planet observations Ms. Sarah Chamberlain Australian Centre for Astrobiology terrestrial planet observations SURF Students 2003: Will Fong, Sam Hsiung, Robert Li (Caltech).

44. The Family of Earths Modern • The oxygen content of the Earth’s atmosphere has significantly changed over 4.6 billion years. Proterozoic Archean

45. Modern Earth 355ppm CO2

46. Proterozoic 0.1PAL O2 100ppm CH4 15% decrease in ozone column depth Segura, Krelove, Kasting, Sommerlatt,Meadows,Crisp,Cohen

47. Archean N2 99.8% 2000ppm CO2 1000ppm CH4 100ppm H2 Karecha, Kasting, Segura, Meadows, Crisp, Cohen

48. F2V G2V Earths Around Other Stars • Modeling self-consistent atmospheres for planets around other stars • Producing spectra of these cases • what we would see looking down from space • what a microbe would see looking up at the sky O3 O3 O2 CO2 Krelove,Kasting,Cohen,Crisp,Meadows

49. Terrestrial Planet Finders Terrestrial Planet Finder NASA Direct detection of planets Launch 2011-2015 Darwin ESA

50. The Terrestrial Planet Finder Mission • Goal: Direct detection and characterization of Earth-sized planets in their habitable zones. • Are there nearby Earth-like planets? • Search 150 stars up to 45 light years away • Do they have atmospheres? • Is there any sign of life? • How to planets form?