In 1995, a breakthrough:the first planet around another star.

A Swiss team discovers a planet – 51 Pegasi –48 light years from Earth.

Artist's concept of an extrasolar planet (Greg Bacon, STScI)7

Didier Queloz and Michel Mayor

Extra-Solar Planetary Systems

And then the discoveries started rolling in:

“First new solar system discovered”USA TODAY

April 16, 1999

“10 More Planets Discovered”Washington PostAugust 6, 2000

“New Planet Seen Outside Solar System”New York TimesApril 19, 1996

Current Planet Count: 331

Stars with Planets: 282

Earthlike Planets: 0

Four of the five planets that orbit 55 Cancri

Artist’sEarthlikePlanet

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.

Radial Velocity Measurement

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.

Astrometry

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

Gravitational Lensing

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 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.

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.

SIM PlanetQuest: Astrometry

• SIM PlanetQuest:– Space-based, 9-meter

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.