11ASTR 1020: Stars & GalaxiesApril 30, 2008 Next class: Review for Final & Wrap-up. Final Exam: May 5, 4:30 – 7:00 pm; Chapters: 1.1-1.2, 4.1-4.4, 5, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23.2The New Worlds Observer:Looking for the Next EarthUsing External OccultersPhil OakleyUniversity of ColoradoApril 30th, 20083Do there exist many worlds, or is there but a single world? This is one of the most noble and exalted questions in the study of Nature. St. Albertus Magnus (1206 – 1280)scholar and patron saint of scientists4ExoplanetsThe Planets That Circle Other StarsThere are probably 10,000 within 10pc (30 light years) of the Earth. Indirect means have now found over 200.If we can observe them directly, we will have a new field of astronomy every bit as rich as extragalactic.5Detecting ExoPlanets:Doppler Technique& Measuring a star’s Doppler shift can tell us its motion toward and away from us. & Current techniques can measure motions as small as 1 m/s (walking speed!).& Newton’s version of Kepler’s 3rdLaw allows us to estimate mass.6First Extrasolar Planet& Doppler shifts of star 51 Pegasi indirectly reveal a planet with 4-day orbital period& Short period means small orbital distance& First extrasolar planet discovered orbiting a “regular” star (1995)27Clicker QuestionSuppose you found a star with the same mass as the Sun moving back and forth with a period of 16 months—what could you conclude?A. It has a planet orbiting at less than 1 AU.B. It has a planet orbiting at greater than 1 AU.C. It has a planet orbiting at exactly 1 AU.D. It has a planet, but we do not have enough information to know its orbital distance.8Clicker QuestionSuppose you found a star with the same mass as the Sun moving back and forth with a period of 16 months—what could you conclude?A. It has a planet orbiting at less than 1 AU.B. It has a planet orbiting at greater than 1 AU.C. It has a planet orbiting at exactly 1 AU.D. It has a planet, but we do not have enough information to know its orbital distance.9Direct Imaging is What We WantCan We Ever Map Extra-Solar Systems In This Manner?10Why Hasn’t This Been Done?& An Earth-like planet is 10 billion (10,000,000,000) times fainter than its host star.& The planet is only 0.1 arcsecond (0.000027 degrees) away from the host star.& Must be done above the Earth’s atmosphere& Mirror’s must be smooth to perfection11New Worlds Observer Diagram& Telescope big enough to collect enough light from planet– 4 meter diameter mirror& Occulter big enough to block star– 50 meter diameter starshade& Telescope far enough back to still see the Earth-like planet– 50,000 kilometers12New Worlds Observer313Fly the Telescope into the Shadow14The ObstacleDIFFRACTIONDespite What They Tell You in Sixth GradeLight Does Not Move In Straight Lines15Occulters& Several previous programs have looked at occulters& Used simple geometric shapes– Achieved only a factor of 100 suppression (need 10 billion)http://umbras.org/BOSSStarkman (TRW ca 2000)16Extinguishing Poisson’s Spot & Occulters can actually concentrate light!& Need an occulter shape that casts a near perfect shadow for the telescope17Fresnel Approximation()222cos20200,iksik ik sikFFFFEe eEeAeddiFπρρθρθρ θ ρλ∞=∫∫()2220200iksikikFFFEke eksEeA J diF Fρρρρρ∞⎛⎞=⎜⎟⎝⎠∫Then, if circularly symmetric:18Starshade ShapePetal shape causes diffracted light to cancel out419Shadow of 16 Petal MaskLinearLog20Effect of Petal NumberPetal ProfilesRadius(m)0 5 10 15 20 25 30 35Log10(Suppression)-16-14-12-10-8-6-4-202648122421Simulated Solar System22http://newworlds.colorado.edu/downloads/NWO.htm23New World Observer Architecture& 4m Telescope Diameter Breakpoint& Two Starshades – one small and fast& Very Powerful Scientifically& Cost comparable to other missions24The First Image of Solar SystemJupiterSaturnUranusNeptuneZodiacal LightGalaxies10 arcseconds525Spectroscopy& Spectroscopy will distinguish terrestrial atmospheres from Jovian with modelingO2H2OCH4NH3S. Seager26It should be possible to detect oceans and continents!27Challenges for New Worlds Observer& Deployment of 50m shade to an accuracy of milli-meters& Flying the starshade and telescope in formation& Fuel usage, retargetting time& Stray Light – particularly from our Sun2829 30NWI Concept1500kmstarshadescollector craftcombiner50,000km1500kmplanet collimatorfield star collimatorprimary collectorto combinerplanet collimatorfield star collimatorprimary collectorto combinerplanet beamsfield star beamsDelay Lines – Mixers - Detectorsplanet beamsfield star beamsDelay Lines – Mixers - Detectors631Earth Viewed at Improving Resolution100 km300 km3000 km 1000 kmTRUE PLANET IMAGING32ConclusionBy 2025O2H2OBy