The Search for Exoplanets

An exoplanet is a planet orbiting a star outside of our solar system The first proven exoplanet was 51 Pegasi, announced in 1995. To date, over 700 planets have been identified.

Ways of Discovering Exoplanets Stars are so much bigger and brighter (+1,000,000x) than planets, it is impossible to just point a telescope at a star and see its planets

Radial Velocity As a planet goes around its star, they both orbit the same center of gravity. The gravity of the planet cause the star to wobble. This back forth wobble is detectable as a back and forth redshift and blueshift of the star

Radial Velocity only works on very large planets, bigger than Jupiter Radial Velocity only works on very large planets, bigger than Jupiter. It also appears to be most effective if the planet is very close to the star. 51 Pegasi, the first exoplanet, is 3 times closer to its star than Mercury. As of May 2012, 702 exoplanets have been discovered using Radial Velocity

Astrometry As telescopes become more and more sensitive, extremely precise pictures of the sky can be imaged. By comparing images taken at different times, you can look for changes in position of the star. This method should be able to detect planets about Neptune-sized, but not as small as the Earth. The method is new, and is yet to discover an exoplanet.

Gravitational Microlensing Gravity from a star or planet causes light to bend. If a star has a planet going around it, this “lensing” will cause it to periodically become brighter and dimmer. This technique is only being done by the University of Warsaw in Poland. They have discovered 15 exoplanets

Pulsar Timing When very massive stars run out of nuclear fuel, they explode, leaving a small dense core, called a neutron star. These remnants usually spin, sending out “blips” of radiation, this is called a “pulsar”. A leftover planet of the dead star can gravitationally alter this spin, which can be measured. 17 exoplanets, with a pulsar as the central star, have been discovered.

Transit Photometry The total light from a star can be measured. If you continuously watch a star, and note that it gets dimmer periodically, that is caused by a planet blocking the light.

The Kepler space telescope (launched 2009), is looking at a tiny patch of sky with powerful enough optics to detect these miniscule differences in light. 61 planets have been confirmed.

Kepler is looking at 150,000 medium to small stars for changes in the light curve of the star. If you were watching a star, and a planet passed in front….what would happen to the light curve? TIME BRIGHTNESS

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