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Martin Ward

Big Question 5: Origin of Planets, and Environments for Life. Martin Ward. Our Solar System – unique or ubiquitous?.

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Martin Ward

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  1. Big Question 5: Origin of Planets, and Environments for Life... Martin Ward

  2. Our Solar System – unique or ubiquitous? A "planet" is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

  3. Mars

  4. The Surface of Titan, (moon of Saturn)

  5. Observational evidence for existence of other solar systems Hubble Space Telescope observations of Orion Nebula (local stellar nursery) – can see protoplanetary discs around protostars

  6. The clearing of a debris disc by a large “Jupiter like” planet

  7. Detecting extra-solar planets Several techniques in use: • Velocity shifts (so-called Doppler wobble) • Transits (eclipses) • Gravitational micro-lensing IV. Pulsar timing V. Direct imaging As of April 2008 we know of 287 extra-solar planets – vast majority from method I, ~10% from method II and 4 from gravitational lensing (Pulsars ?)

  8. The Velocity Shift, Method I Earth = 0.1 m/s Jupiter = 12.4 m/s Neptune = 0.3 m/s

  9. What type of solar systems do we find?

  10. The Transit, Method II

  11. Gravitational Micro-lensing

  12. Showing type of planet detected by microlensing

  13. Pulsar Planets? Highly accurate periodic signal, modified by the presence of a planet. However, this will not be a normal planet because of supernova explosion

  14. Can we “see” an extrasolar planet?

  15. Early suggestions of life on other planets… Giordano Bruno 1548-1600 …claiming the existence of the plurality of worlds

  16. Where could we live?The Goldilocks constraint • What are the necessary conditions for life to emerge and flourish? • We assume require a terrestrial planet • This planet must support liquid water • For this we require conditions that are neither too hot nor too cold, but just right…

  17. Galactic Habitable Zone Too close to centre - high stellar density increases planetary system disruption; AGN, SN and GRBs sterilise planets Too distant from centre - low metallicity - insufficient heavy elements for terrestrial planets to form Galactic Habitable Zone

  18. Temperature of planets • For life: require liquid water at surface of planet - temperature of the planet is critical Consider example of Earth: heat energy in from Sun balanced by Earth’s thermal emission

  19. Our solar system’s Habitable Zone • Putting Earth/Sun values into equilibrium temperature equation gives TEarth = 255 K or minus18ºC ! • But actual mean surface temperature of Earth at ~ 15ºC (fortunately for us…) • We are saved by the - greenhouse effect

  20. Greenhouse effect can be critical for life • Earth has mild effect (difference ~ 33 K) • Venus is in Sun’s HZ - but surface temperature of ~740 K! • Difference: runaway greenhouse effect • Earth has not suffered this (due to lower carbon cycling via plate tectonics)

  21. Properties of planet lying in HZ Now - what about the future? • Inner and outer radius of Habitable Zones varies with the type of star

  22. Interferometry and extra-solar planet studies • Can gain improve resolution by using two or more separate telescopes as an interferometer - d is the separation of the telescopes • Limit then from “wobble” of Earth’s atmosphere (seeing) • Ground-based telescopes used as interferometers e.g. Keck, VLT VLT Keck

  23. Space missions NASA: Kepler • ~ 1m telescope • Quite small field of view • Monitors 100000 stars for 4 years • Will detect at least 50 Earth-like systems kepler.nasa.gov Launch: Feb 2009

  24. Space Missions ESA: Darwin

  25. Nulling Interferometry

  26. Vital signs for Life Atmospheric changes imprint distinct spectral signatures - this could be used to identify inhabited planets

  27. So… what’s the relevance of all this for Durham University ? Theory

  28. Question: is the moon important for the evolution of life?

  29. Question: how do big planets get so close to their stars?

  30. Modeling of protoplanetary discs

  31. Observations we build advanced instruments

  32. Durham in Space!

  33. Thomas Wright of Durham An Original Theory, or New Hypothesis of the Universe, 1750

  34. Durham University Observatory

  35. Durham returns to study of planets?

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