Download Extrasolar planets

Extrasolar planets
Finding planets
Finding planets around other stars is
hard!
need to look for something very faint
very close to something that is MUCH
brighter!
In the past 10-15 years, astronomers
have gotten very clever and it has paid
off!
I. Finding planets indirectly by
gravity
– Orbit can’t be seen
directly
– But the motion can be
detected by the Doppler
shift if it is oriented
correctly relative to our
line of sight
Doppler Measurements Yield
Planet Mass
Mass = 4.6 M
II. Finding planets indirectly by
light
• If the orbit of a planet lines up just right
from our perspective, it might pass in
front of its parent star
• This makes a sort of eclipse called a
transit
Transit Yields Planet Radius
10b Size
Radius = 1.4 R
Transits and Kepler mission
• Problem: dimming is small, determined
by relative size of planet and star
– Very small for Earth sized planets!
• Has been detected for large planets
• Kepler mission is currently searching for
Earth-sized planets!
NASA’s Kepler Mission
Determining the frequency of Earth-size and larger planets
in the habitable zone of Sun-like stars
Extrasolar planet detections
• Lots of planets (>500!) have been
detected, all in the last 10-15 years
• For most of these, we don’t know what
the planets are made of, but for the few
we can tell, they are probably gas
planets like Jupiter
• At least, until this week ….
Kepler 10-b
• Just announced
this week!
• Earth-sized planet
• Very close to its
parent star, so
very hot
Transit and Doppler
Measurements Yield Density
+
10b Size
Density
Mass = 8.8 g/cm3
Volume
Composition of Kepler-10b
Summary
• Kepler-10b is orbiting a star very much
like our own Sun, but with an age
greater than 8 billion years, at a
distance of 560 light years.
• Kepler-10b is the smallest exoplanet
discovered to date and the first
unquestionably rocky planet orbiting
a star outside our Solar System
Gliese 581
• Multiple planet system with a
planet in a habitable zone?
– Low mass M star, so
habitable planets are close
– Seven planets have been
suggested!
– Gliese 581g has a period of
37 days and is predicted to
be in the habitable zone!
– Gl 581g is “tidally locked” to
star, meaning same side
always faces the stars