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 MissionDetermining 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 DopplerMeasurements Yield Density
+10b Size
MassVolume
= 8.8 g/cm3
Density
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 exoplanetdiscovered to date and the firstunquestionably rocky planet orbitinga 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