Transcript Slide 1
Extra-Solar Planetary Systems In 1995, a breakthrough: the first planet around another star. Didier Queloz and Michel Mayor A Swiss team discovers a planet – 51 Pegasi – 48 light years from Earth. Artist's concept of an extrasolar planet (Greg Bacon, STScI) 7 And then the discoveries started rolling in: “New Planet Seen Outside Solar System” New York Times April 19, 1996 “10 More Planets Discovered” Washington Post August 6, 2000 “First new solar system discovered” USA TODAY April 16, 1999 Four of the five planets that orbit 55 Cancri Current Planet Count: 331 Stars with Planets: 282 Earthlike Planets: 0 Artist’s Earthlike Planet Radial Velocity Measurement A planet orbiting around its parent star exerts a pull that causes the star to 'wobble' around the center of mass between the two objects. If the system is oriented nearly edge-on to the Earth, the movement of the star toward and away from the observer will cause its light to be slightly blue and red shifted respectively. Telescopes outfitted with precise spectrometers can measure this small shift with respect to dark absorption lines in the spectrum. For this reason, radial velocity measurement is also known as doppler spectroscopy. Astrometry As a planet revolves around its star, it pulls the star around through its orbit. If the system is oriented face-on and the orbiting planet is massive enough, this small motion of the star can be detected by astrometry. As the planet moves through its orbit (red dots), the star revolves around the system's center of mass, called the barycenter (the black cross). In an actual planetary system, the star's mass is so great compared to the planet's, that the barycenter will most likely lie within the star itself, and the path in which it moves (blue dots) will be a much smaller circle. Astrometry, therefore, relies on very precise measurement of a star's position. Gravitational Lensing Gravitational lensing occurs when a background object's light is bent due to the gravity of the foreground object. A lightcurve from a stellar lensing is generally smooth, so when a companion planet of sufficient brightness also moves behind the 'lens', a perturbance in the lightcurve results Transit of Extra-solar Planet (Photometry) (“nearby” = within 660 LY) Jupiter An image of Upsilon Andromedae, a solar-type star, 44 light years away, with three large planets orbiting it. 47 Ursae Majoris (45.9 light-years from Sol) is a yellow-orange main sequence dwarf star of spectral and luminosity type G0-1 V, with about 1.03 times the mass of Sol, 1.26 times its diameter, and 1.54 times its luminosity. The star may be less than or as enriched (83 to 102 percent) as Sol with elements heavier than hydrogen based on its abundance of iron. It may be around 6.32 billion years old. The two-planet system bears an intriguing resemblance to our own. The mass of the inner planet at 2.5 times that of Jupiter, at least, while the newly discovered outer planet has a mass at least 3/4 that of Jupiter. The average distance from the star to the inner planet is 2.09 AU, the outer planet is 3.73 AU from the central star. 55 Cancri is a double star system about 40.9 light years from Sol. Star A is a G8 V yellow dwarf, older and dimmer than our sun. Star B, 1065 AU from the primary, is a faint M4 V red dwarf. It is around 55 Cancri A that a retinue of planets has been recently detected. 55 Cancri was the first quadruple planetary system discovered, and continues to be a prime target for observation. More planets in this system are likely to be detected in coming years. SIM PlanetQuest: Astrometry • SIM PlanetQuest: – Space-based, 9meter baseline, optical interferometer operating in the visible band – Micro-arcsec accuracy – Detect Earth-like planets – Scheduled launch ~2015 Kepler Mission observing Transits • Kepler mission: – 0.95-meter space telescope – Continuously monitor ~100,000 stars – Capable of detecting Earth-like planets – Scheduled to launch in 2009 – Four year mission Terrestrial Planet Finder (~2014) TPF will measure the size, temperature, and placement of planets as small as the Earth in the habitable zones of distant solar systems. TPF's spectroscopy will allow atmospheric chemists and biologists to use the relative amounts of gases like carbon dioxide, water vapor, ozone and methane to find whether a planet someday could or even now does support life.