Exoplanets Searching for New Worlds Larry Morgan

1. Exoplanets Searching for New Worlds Larry Morgan

2. Exoplanets • “(There are) countless suns and countless Earths all rotating around their suns” - Giordano Bruno, 1584 • Speculation since Ancient Greeks • Proposed by Isaac Newton in 1713 • Various claims of discovery since 1855 • First confirmed detection 1988 by Bruce Campbell, G. Walker and S.Yang

3. Campbell, Walker & Yang discovered a massive planet using the radial-velocity method However, first convincing exoplanet discovered in 1992 by Wolszczan and Frail by pulsar timing method

4. Detection Methods • Radial Velocity Method

5. Doppler Shift

6. Detection Methods • Radial Velocity Method

7. Detection Methods • Radial Velocity method

8. Pulsar Timing

9. Astrometry • Images ‘wobble’ of stars directly • Extremely difficult • Kaj Strand claimed detection using this method in 1943 at Sproul Observatory • Other claims followed in 1960 and 1963

10. Gravitational Lensing • Usually seen on much larger scales • Several detections made

11. Transit Method • Most popular and ‘easiest’ • Very powerful, especially when combined with radial velocity method

12. Transit Method • Mass, period and composition determinable • corollary - reflected/refracted light direct measurement of atmospheres possible

13. First exoplanetary atmosphere detections were of sodium • Sodium easy to detect, first milestone toward other chemicals • Light from the star passes through the atmosphere of the planet on its way to us • The original starlight can be filtered out to leave only the effects of the planetary atmosphere • This method originally dates from around 300 years ago

14. Selection Effects • Estimated 10 billion planetary systems in our Galaxy (100 billion stars) • As of January 2009 there are 335 exoplanets known • Science still in early phases

15. ‘Hot Jupiters’ • Our current methods of detection work best for big planets close in to their stars • Nearly all exoplanets currently discovered are bigger than Jupiter, the biggest planet in our system • Most of these are closer to their star than Mercury is to the Sun

16. Massive Exoplanets

17. Why so Big? • Why are so many exoplanets large and close in? • Nearly all methods of detection most sensitive to higher mass & shorter orbits

18. Astrometry - Stellar Wobble • Radial Velocity • Pulsar Timing • Gravitational Lensing • Photometry - Transit

19. Eccentricity • Majority of known exoplanets have eccentric orbits • Inexplicable by selection effects

20. Plot showing planets detected up to 31st August 2004 • Lines show limits of survey methods • Shaded areas-expected progress 2006-2010 • Solar planets indicated (V,E,M,J,S,U,N) • Detected planets drawn with colours indicating detection method • Blue – Radial Velocity • Red – Transit • Yellow – Microlensing

21. Earth-like Exoplanets • As of August 2008 only 12 exoplanets have masses less than 10 Earths • The fact that any ‘Earth-like’ exoplanets have been discovered at all indicates that they are probably very common • According to one experiment, 1 in 14 stars may be host to ‘Hot Jupiters’ while 1 in 3 host rocky Earths

22. Implications for Planet-Formation • Finding such massive planets so close to their parent stars contradicts much of established theory • Planet-formation theory is hard to test, largely known through computer simulation

23. Planet-Formation • Rocky planets form close to stars • Outer planets gaseous because of lower temps

24. Planetary-Formation • If our picture of planetary formation is correct, how did the hot, massive exoplanets we observe come to be so close to their suns? • Planets may have formed in outer disk and migrated inward

25. Planetary-Formation • Gas-Disk Migration - Forming planet loses energy through interactions with protoplanetary disk • Planetesimal-Driven Migration - Formed planets eject planetesimals resulting in loss of energy - probably responsible for Neptune’s orbit • Planet-Planet Scattering - Numerical simulations show that this is likely mechanism for observed eccentricities

26. Sexier Stuff • Attitudes within the Astronomical community have steadily changed over the last ten years, at least outwardly • Professed goal of planet-finding is now regularly stated as ‘finding life’ • The progression towards smaller, more Earth-like planets leads to an almost inevitable conclusion

27. Aliens!!

28. The Drake Equation • N - Number of communicable worlds • R* - Rate of star-formation • fp - Fraction of stars with planets • ne - Number of planets capable of supporting life • fl x fi x fc - Fraction of planets that develop intelligent life capable of communicating beyond their planet • L - Length of time such civilisations emit communications

29. The Drake Equation • N is what we care about • R* - Well known • fp - Pretty well known, at least educated guess • ne - Knowable • fl x fi x fc - Can only guess, possibly unknowable, at least on reasonable timescale • L - Completely hypothetical

30. The Drake Equation • The Drake Equation summarises current knowledge.. as of 1960 • Which is to say.. the equation is largely meaningless

31. SETI • The Search for Extra-Terrestrial Intelligence • www.seti.org • SETI@home • Dyson Spheres

32. Dyson Spheres • Artificial structure, capturing most or all of a star’s energy output • Such a structure would output a recognisable thermal signature • Scientists at Fermilab have so far identified 17 candidates from more than 10,000 observations

33. Dyson Spheres • “I think the search... is looking for a needle in a field of haystacks, when you’re not even sure there’s a needle there.” • “If you can build a Dyson sphere, then you don’t need it.”

34. More Relevant Issues • Percentage of ‘Earths’ - Basically the Drake Equation, or at least the relevant portion • Habitable zones • Planetary habitability • Planetary atmospheres

35. Habitable Zones • The Circumstellar Habitable Zone is the region of space in which life would be favourable for life as found on Earth

36. Habitable Zones • Criticisms • We have very little knowledge of what life on other planets might need to evolve, carbon-based or otherwise • Circumstances might mean that favourable conditions might develop outside the CHZ (e.g.Europa) • Breathable atmosphere requires plant life (photosynthesis) • Planets move, life can adapt (though more likely if a planet has moved out of CHZ)

37. Planetary Habitability • NASA has defined the principal habitability criteria as “extended regions of liquid water, conditions favourable for the assembly of complex organic molecules, and energy sources to sustain metabolism.” • Many other relevant factors, e.g. ‘Good Jupiters’ which shield planets from cometary impacts, shepherd orbits, even supply early planets with volatile components necessary for the introduction of life

38. Planetary Atmospheres • E.g. Oxygen, Carbon Dioxide and Methane • Oxygen is only present on Earth thanks to early cyanobacteria and eventually photosynthesising plants • Without the right mixtures of liquids and gases a good CHZ is pretty irrelevant

39. So...? • If what we’re looking for is another Earth, how far have we come?

40. Planet Discoveries

41. Planet Discoveries

42. Finding Other Earths • May need to go below Earth’s mass when looking for life

43. Finding Other Earths • Even if we find another Earth with life on it, would we be able to detect it? • Galileo Probe (left) searched Earth on a flyby for the ‘Sagan Criteria for Life’

44. Finding other Earths • Red absorption - Plants • Oxygen absorption lines - Plants again • IR spectral lines - Methane • Narrowband modulated Radio - Technology

45. Fomalhaut B First Visible Light Image of a Planet Orbiting Another Star • November 14th • 25 light years away • 3 MJ • 23 x Sun - Jupiter Distance • Ring like Kuiper-Belt

46. Future Missions • Kepler • Launching in 2009 • Will find and characterise 100s of terrestrial planets • Will find out the mix of planet types • Orbit characteristics • How does stellar type affect type of planetary system? • How are we proceeding?

47. Future Missions • SIM Planet Quest • Under development-hopeful launch mid 2010s • Search 250 nearby stars for terrestrial planets • More accurate astrometry than ever before • How are we proceeding? After searching nearby stars for ‘Earths’ will look farther afield for ‘Neptunes’, as many as 2000 Mission tied to the two TPFs

48. Future Missions • Terrestrial Planet Finder - actually two missions, a coronagraph and an interferometer • No launch date at present, though funding promised along with Europa mission • How are we proceeding? Capable of identifying life through atmospheric chemical signatures 200 stars within 45 lyr of Earth

49. Future Missions TPF - C - (left) Direct optical characterisation of size and composition of other Earths TPF - I - (right) IR measurements of temperature, size and composition of same • How are we proceeding? Measurements of atmospheric signatures such as water, carbon dioxide and ozone (life) and sulfur dioxide and carbon monoxide (industrial)

50. Future Missions CoRoT - Convection Rotation and Planetary Transits • How are we proceeding? Measurements of atmospheric signatures such as water, carbon dioxide and ozone (life) and sulfur dioxide and carbon monoxide (industrial) Launched in 2006 Measures transits similarly to Kepler Will measure 120,000 stars Also capable of measuring properties of stars