Extrasolar planets. Finding planets Finding planets around other stars is hard! need to look for...

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