WILLIAM & DEBORAH HILLYARD

Extra Solar Planets

Description

Exoplanet Status:
For centuries, human beings have wondered whether other planets existed orbiting other stars.  In fact, in 1584 Giordano Bruno, a Catholic monk, suggested  that the Universe was infinite, and that there were "countless suns and countless earths all rotating around their suns".  The church accused him of heresy,  and burned him at the stake in 1600.  Until recently, the technology to  determine this has been beyond our grasp.  Recent advances in science and  technology have answered this question with the discovery of numerous planets orbiting stars other than our Sun.  However, technology still has some  limitations, and the planets discovered to date have all been much more massive than our Earth; in fact, most are close to the size of Jupiter and larger,  and are probably gas giants rather than rocky planets.  Many of the systems found could harbor Earth like planets, but we need much more sensitive  instruments to detect them. 

We should also provide some definition of what constitutes a planet, as many of those found around other stars have been enormous; substantially larger than our largest planet Jupiter.  Essentially, once an object's mass reaches about 13 times the mass of Jupiter, gravitational collapse will cause it to heat to the point when deuterium fusion starts, so it is classified as a Brown Dwarf Star.  Anything less than 13 Jupiter masses is a planet.  We are unlikely to be able to identify anything as small or smaller than the Earth for some time, so the question of  "how small is a planet" is not relevant; yet. 

So; how are planets found?  This link to NASA contains a brief outline of the methods used.  It  is virtually impossible to image planets due to the enormous distances to even close-by stars, and the fact that they would be lost in the glare from their  parent star.  However, some planets have been imaged after they were found using other, indirect methods.  There is a wealth of information on extra solar planets in this section of The Neighborhood website

In this section, we look at some of the stars and their planets.  Some are included in the Solar System Visualization; just follow the instructions on the screen. 
Date Number of
Exoplanets
Number of
Systems
Number of Multiple Planet Systems
December 6th, 2011 708 581 78
February 29th, 2012 760 609 100
February 21st, 2013 861 677 128
September 18th, 2013 974 744 162
March 5th, 2014 1,078 815 179
December 10th, 2014 1,854 1,163 473
April 12th, 2016 2,107 1,349 511
March 17th, 2017 3,594 2,695 606
As of March 2017, NASA's Kepler spacecraft, designed to look for new exoplanets, has identified 2,331 confirmed exoplanets and 4,696 potential planets.  The table to the right records the total number of confirmed exoplanets, over time, from all sources.  The information comes from The Extrasolar Planets Encyclopedia, where there is a great deal of additional data. 
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