The Exoplanets: The Other Solar Systems.

A Planet is an object that has a mass between that of Pluto and the Deuterium-burning threshold that forms in orbit around an object that can generate energy by nuclear reactions. Exoplanets are planets that exist outside of our solar system. Scientists always discover new exoplanets. The discovery of such planets raises multiple questions. Only in the relatively recent past have we been able to discover and study extrasolar planets.

Introduction

The Exoplanets are planets outside of our solar system. Today there are 347 according to NASA. Of the 347 planets, 243 are gas giants, 80 are hot Jupiters, and four are pulsar planets. A majority of the exoplanets we have discovered are contained within 300 light years of our sun. So far, 292 star systems contain exoplanets.

How are extra solar planets discovered?

The Hubble Telescope was launched in 1990. The Hubble orbits the Earth, above the light obscuring atmosphere, giving it a clearer picture of the cosmos. This is one of the prime ways we gain information on exoplanets. Other such projects include:
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Spectrometer
The Properties of Exoplanets orbiting other stars
Exoplanets primarily consist of either terrestrial or gas giants. Terrestrial planets are planets that are primarily composed of silicate rocks, such as Earth and Mars. Gas giants are mostly composed of hydrogen, helium, and water, such as Jupiter and Neptune. There are more gas giants than terrestrial planets. No exoplanets have been found to be Earth-like.
The smallest exoplanet discovered so far is planet "e" in the Gliese 581 system. "E's" mass is only about twice that of Earth. Terrestrial planets are fairly uncommon. The methods that we use to observe these planets, however, only allow us to speculate on the make-up of many of these bodies.
A small number of exoplanets orbit pulsar instead of stars. These planets are known as pulsar planets. Pulsars are dense, spinning remnants of a supernova explosion.

New Discoveries
On April 21st 2009, the discovery of the newest exoplanet was announced at the European Week of Astronomy & Space Science. This recent discovery has brought a previously discovered exoplanet under speculation. Gliese 581 d is the farthest out planet in the system and is believed to be too massive to be mostly terrestrial. Recent observations have lead to the speculation that "d" is an icy planet that has moved closer to the star. Being so, it is the first real candidate for an ocean covered exoplanet.
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Interferometry
When two waves, notably light, meet at the same time and space, interference is caused. Interferometry uses this phenomena for the measurements of the wavelengths and amplitudes of optical waves. Astronomers use multiple telescopes, and through interferometry combines them to the effect of a much larger telescope. Because of the multiple waves being focused, the wavelengths and amplitudes are matched up to create a clearer image. The process also allows astronomers to block out the light from stars and create a higher resolution picture of distant exoplanets. This process has been in effect for around 15 years and has contributed to the recent spike in extrasolar discoveries.

Bibliography
http://planetquest.jpl.nasa.gov/science/science_index.cfm
http://planetquest.jpl.nasa.gov/technology/technology_index.cfm
http://planetquest.jpl.nasa.gov/overview/overview_index.cfm
nexsci.caltech.edu/missions/Palomar/
http://hubblesite.org/
planetquest.jpl.nasa.gov/SIM/whatisSIM/
http://www.seti.org/Page.aspx?pid=352
nexsci.caltech.edu/