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General Astronomy Formation of Solar Systems Observational Evidence And Some Surprises “Are there somewhere, other worlds like ours?” -- Epicurus, 300BC Copyright 2003 Kimmo Isokoski Other Worlds After 2,300 years, we can finally answer the question. “Yes, Epicurus. There are other worlds orbiting about distant suns.” By Spring 2015, we had discovered over 1915 planets / 1210 planetary systems / 481 multiple planet systems Beginning the Search "We shall be less apt to admire what this World calls great...when we know that there are a multitude of such Earths inhabited and adorn'd as well as our own." "...so many Suns, so many Earths ...And how must our Wonder and Admiration be increased when we consider the prodigious Distance and Multitude of the Stars." Christiaan Huygens, ‘The Celestial Worlds Discover'd: Conjectures Concerning the Inhabitants, Plants, and Productions of the Worlds in the Planets’, 1690 Of course, in 1690, there was little chance of actually observing planets about stars other than our sun. We have had to wait 300 years before it became possible Beginning the Search In 1916, E.E. Barnard published a report of a star with the extremely large proper motion of 10.3 arcseconds per year. It is a small, red star named (appropriately) ‘Barnard’s Star’ It’s motion is large because it is only about 5.9 lightyears distant. In fact, it is moving toward us (or we’re moving toward it) and it will only be 3.8 lightyears away by 11,800 AD Because of the motion, and distance, it is a good candidate to look for a planetary system. Barnard’s Star • Starting in the late 1930’s, Peter van de Kamp began a lifelong project devoted to proving Barnard’s Star harbored planets. • Working at Sproul Observatory (Bryn Mawr College, Philadelphia), he began taking accurate photographs of Barnard's Star • Using 2000 photos (1937 – 1962), van de Kamp looked for a telltale wobble in the proper motion of the star against be background of the more distant stars. Methods Before discussing van de Kamp's results, let's look a the ways an extra-solar planet might be detected: • • • • Astrometry Direct Observation Radial Velocity Photometry Astrometry Astrometry is the precise measurement of the positions of astronomical objects. A star and planet act gravitationally on each other. The planet is pulled about the star and vice versa. In reality, they both orbit a common center of mass (generally nearer to the star). This causes a wobble in its path as seen against the background of distant stars Looking for the Wobble Proper Motion No Planets 1940 One or more planets 1960 1980 2000 Direct Observation • Based on observing the reflected light of the parent star • Only extremely large planets may be detected using this method • The overwhelming brightness of the parent star makes the planet very hard to detect • Another method for direct observation looks for the IR signature of a dust disk surrounding the star and can, in fact, even locate gaps in the disk indicating the presence of planets. Dust about 55 Cancri Hubble’s view of protoplanetary disks Radial Velocity • As in astrometry, this technique looks for a wobble in the star’s motion. Instead of looking for small side-toside movement (I.E. in proper motion) this looks for wobbles in the radial direction using doppler shift. Looking for the Wobble Radial Velocity Photometry • This method measure very precise values of a star’s brightness. When a planet ‘transits’ the star, it’s brightness dims by a very small – but measurable - amount. • Based on the shape of the resulting lightcurve, a planet may be inferred Planetary Transit Kepler KEPLER 2009 Detection ofof Detection Exoplanets: Exoplanets: Planetary Planetary Transit Method Transit Method Photometry of HD209458 Where to Look? Nearby stars are the best because: Planets are brighter. The angular separation between planets and the star is larger Stars are brighter Doppler shifts easier to measure Motions on the sky easier to measure Stars with distance less than 10 parsecs from the Sun Spectral Class Mass M NTotal NSingle A 1.8 - 3.4 2 0 F 1.1 - 1.8 11 5 G 0.8 - 1.1 26 13 K 0.5 - 0.8 42 18 M < 0.5 210 63 Back to Barnard's Star Controversy and more controversy. Over the years, van de Kamp refined his calculations and published changes to ‘his planets.’ Originally a single very massive planet in an eccentric orbit; they became 2 planets, one slightly bigger than Jupiter and the other slightly smaller in nearly circular orbits. By 1985, when van de Kamp published a final paper on his discovery, other astronomers, using different telescopes, could not find the distinctive wobble. One went so far as to suggest that the wobble was in the Sproul Telescope rather than in the star. Others claimed they detected a wobble, but not the same as van de Kamp (his rebuttal reflected the fact that he had spent over 40 years looking a thousands of photographic plates and therefore knew best). At this point in time, the ‘jury is still out’ and we really don’t know if Barnard’s Star was the first discovery of extra-solar planets. Types of planets • • • • Classic Jovian Epistellar Jovian Terrestrial Pulsar Planets A sampling of extrasolar systems New Earth-like Planet! The star is a red dwarf with spectral type M3V, located 20.3 light-years away from Earth. ? The First Images of Exoplanets One planet orbiting Fomalhaut Star location • New images show planets orbiting bright young nearby stars • Although more than 350 planets are known to orbit other stars, none could be imaged until now Neptune-sized orbit Hubble Space Telescope visible image of the star Fomalhaut (whose light was blocked), with a dust belt similar to the Kuiper belt. Inset: Images taken ~2 years apart show a planet moving around the star. Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider [email protected] - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009 One of a few images of an exoplanet around a star Glowing Young Planets • This star has three orbiting planets the first imaged planetary system! • Planets are much fainter than their parent star, so are difficult to image • Why are these pictures possible? • Advanced observing techniques were used to block the star’s light • Observations were repeated over years, confirming planetary motion • The planets are young and hot, and therefore glow more brightly than by reflected starlight alone Three planets orbiting HR8799 Keck Observatory infrared image of star HR8799 and three orbiting planets with orbital directions indicated by arrows. The light from the star was subtracted, but a lot of ‘noise’ remains. Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider [email protected] - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009 The Big Picture • Previous exoplanet detections were indirect (used stellar motion and transit methods) • These are the first pictures of planets around other stars • Ever-improving images from Earth and space should allow us to detect smaller (more Earth-like) planets • Images and spectra at different wavelengths will allow us to measure the composition of exoplanet atmospheres, and determine whether they are habitable. Artist’s conception of a planetary system orbiting another star. Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider [email protected] - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009 First Rocky Exoplanet Detected • Most known exoplanets are large and have low densities - similar to jovian planets in our solar system • A space telescope recently discovered a planet with radius only 70% larger than Earth’s • Groundbased observations show the planet’s mass is less than 5 times Earth’s • Together, the observations reveal that the planet’s density is similar to Earth’s - the first confirmation of a “rocky” exoplanet Artist’s conception of the view of the rocky planet’s parent star (Corot-7) from above the surface of the planet (Corot-7b). Image from ESO / L. Calcada. Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider [email protected] - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009 How Can We Find a Planet’s Density? • Density = Mass / Volume • The planet’s mass was determined using the radial velocity method: Changes in a planet with mass ~5 times Earth’s. the measured wavelengths of star light are caused by • Volume = 4/3 R3 • The planet’s size was determined using the transit method: The amount of light measured from a star decreases when a planet passes in front. The amount of decrease indicates the planet’s size. Amount of Light The planet gravitationally ‘tugs’ on the star, shifting the wavelength of light the star emits back and forth. The amount of shift indicates the planet’s mass. -4 0.04% -2 0 Hours 2 4 Periodic decreases in light from the star are caused by a planet with diameter 1.7 times Earth’s passing in front. The Big Picture • After discovering hundreds of exoplanets resembling our jovian planets, astronomers have found the most Earth-like planet to date • Although planet Corot-7b’s density is close to Earth’s, differences abound: it orbits its star in ~20 hours (faster than any known exoplanet) - so close that its rocky surface may be molten • With the existence of Earth-like planets now demonstrated, astronomers have reason to hope that the Kepler mission will discover more Detection of more rocky exoplanets (‘Super-Earths’) like those in this artist’s depiction should come rapidly, thanks to dedicated space telescopes and improving ground-based detection capabilities. Image from D. Aguilar, Harvard Smithsonian CfA. Kepler 186f A newly discovered (17 APR 14) planet nicknamed "Earth's cousin" has been found 492 light-years from Earth. The planet, called Kepler-186f is the first Earthsize planet found in the habitable zone of its star. Ten percent larger than Earth, Kepler-186f is the closest planet to Earth in size ever found in the habitable zone of its star. Artist’s Concept The newly discovered exoplanet orbits about 32.5 million miles (52.4 million kilometers) from its sun. It takes Kepler-186f about 130 days to orbit its red dwarf star. The Kepler-186 star is about half the mass of the sun, and the newly discovered planet is far enough away from its star that powerful flares may not greatly affect the planet. To be considered… • Assuming that the planets are ‘real’ how does this change our models of the formation of solar systems? • First, it helps to show that solar systems are not freak occurrences, but common, natural phenomenon • We have to reconsider, how gas giants can form near a star (epistellar Jupiter's) rather than far out where it is cool. Press Releases • For More Information… Space.com - 09/16/09 - “First Rocky World Confirmed Around Another Star” http://www.space.com/scienceastronomy/090916-rocky-exoplanet.html • Eurpoean Southern Observatory - 09/16/09 - ‘First Solid Evidence for a Rocky Exoplanet’ http://www.eso.org/public/outreach/press-rel/pr-2009/pr-33-09.html Images • Artist depiction of Corot-7 system courtesy European Southern Observatory / L. Calcada http://www.eso.org/public/outreach/press-rel/pr-2009/pr-33-09.html • • • Detection method cartoons - 2006 Pearson Education Inc., publishing as Addison Wesley Transit and radial velocity data plots adapted from source articles below Artist depiction of Super-Earth courtesy David Aguilar, Harvard Smithsonian CfA http://www.cfa.harvard.edu/news/2008/pr200802_images.html Source Articles • (on-campus login may be required to access journals) Léger et al., ‘Transiting exoplanets from the CoRoT space mission VIII. CoRoT-7b: the first Super-Earth with measured radius’, Astronomy and Astrophysics, in press, 2009. http://www.aanda.org/articles/aa/pdf/forth/aa11933-09.pdf • Queloz et al., ‘The CoRoT-7 planetary system: two orbiting super-Earths’, Astronomy and Astrophysics, in press, 2009. http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361/200913096 Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider [email protected] - http://dps.aas.org/education/dpsdisc/ - Released 3 December, 2009 For more information… Press Release / News Story • New York Times - 11/13/2008 - “Now in Sight: Far-Off Planets” http://www.nytimes.com/2008/11/14/science/space/14planet.html Images • Hubble image of Fomalhaut B Taken from the source article by Kalas et al. • Keck image of HR8799 Taken from the source article by Marois et al. • Artist concept of another planetary system from Gemini Observatory http://tinyurl.com/geminiplanetfamily Source Articles • (on-campus login may be required to access journals) Kalas et al., ‘Optical Images of an Exosolar Planet 25 Light-Years from Earth’, Science, 322(5906), p. 1345 DOI: 10.1126/science.1166609. http://www.sciencemag.org/cgi/content/abstract/322/5906/1345 • Marois et al., ‘Direct Imaging of Multiple Planets Orbiting the Star HR 8799’, Science, 322(5906), p. 1348 DOI: 10.1126/science.1166585, 2008. http://www.sciencemag.org/cgi/content/abstract/322/5906/1348 Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider [email protected] - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009 Links http://exoplanets.org/ http://exoplanet.eu/index.php http://www.public.asu.edu/~sciref/exoplnt.htm http://www.astro.uiuc.edu/~kaler/sow/pp.html http://www.msnbc.msn.com/id/11022898