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