Download without video - Scott Marley

2012
ASTRO SUMMER SCHOOL
EXOPLANETS
Historical Background
In the sixteenth century the
Italian philosopher Giordano
Bruno put forward the view that
the fixed stars are similar to the
Sun and are likewise
accompanied by planets.
He was burned at the stake by
the Roman Inquisition in 1600,
though his views on astronomy
were not the main reason for his
condemnation.
First Confirmed Discovery
On 21 April 1992, radio astronomers Aleksander Wolszczan
and Dale Frail announced the discovery of two planets
orbiting the pulsar PSR 1257+12.
This discovery is generally considered to be the first definitive
detection of exoplanets. These pulsar planets are believed to
have formed from the unusual remnants of the supernova that
produced the pulsar, in a second round of planet formation,
or else to be the remaining rocky cores of gas giants that
somehow survived the
supernova and then
decayed into their
current orbits.
First planet around a main
sequence star
On 6 October 1995, Michel Mayor
and Didier Queloz of the
University of Geneva announced
the first detection of an exoplanet
orbiting 51 Pegasi.
It was discovered via the transit
method.
Doppler Method
As a planet orbits a star, both
objects orbit around the center of
mass. The movement of the star
can be detected by looking at its
spectral lines – we can now detect
velocities below 1ms-1.
This method has so far found the
highest number of exoplanets,
although it can only be used to
find a lower limit on the planet’s
mass, not the actual mass
Transit Method
If a planet crosses in front of the star, it will create a small drop
in the apparent brightness. This enables us to measure the size
of the planet but only works for systems in the correct
orientation.
Transit Timing Variation
Gravitational Microlensing
Microlensing occurs when the gravitational field of a star acts
like a lens, magnifying the light of a distant background star.
Planets orbiting the lensing star can cause detectable
anomalies in the magnification as it varies over time.
Pulsar Timing
Pulsar timing can detect planets less than a 10th of the mass
of Earth. Unfortunately these planets would not be habitable.
Direct image of exoplanets around the star HR8799
Infrared image of 2M1207 and 2M1207b
Formalhaut b
How many stars have planets around them?
It is difficult to give a definitive answer to this. We have only
just started our discovery of exoplanets but so far, the
numbers look something like this:
1-1.5% of sun-like stars have hot jupiters.
20% of sun-like stars have at least one giant planet.
40% of sun-like stars have planets of lower mass.
In total it is estimated that the Milky Ways contains 10-200
billion planets.
< 300 light years
What type of stars have planets?
Most currently known planets orbit around sun-like stars, but
this is mainly because current observing programs tend to
concentrate on these types.
The smallest type M stars probably don’t
have planets, the largest O type are so
hot that they produce a photoevaporation effect that stops planets
from forming.
What is the mass of most planets?
As of 2012, all but 50
known exoplanets are
over 10 times the mass
of the Earth. This is
because larger planets
are easier to detect.
Initial results from the
Kepler spacecraft show
that low mass planets
are probably far more
common than high
mass.
Predicted sizes of different planet types
Isolating a Planet’s Spectrum
Comparing the spectrum to models
Detecting water in HD 189733b
Measuring the temperature of the surface
Which exoplanets are habitable?
Upsilon Andromedae d
The Kepler Mission
Kepler’s focal plane (camera)
Kepler Results
As of 28th June 2012, Kepler has discovered and confirmed 74
planets.
There are currently 2321 planet candidates that need to be
followed up with more observations.
Data Visualisation