Download 17.Extra-solar

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.