Friday, September 28, 2018

Planets outside our own



- 2107 -  Planets outside our own.  -  There are 300,000,000,000 stars in our galaxy. There are 
2 trillion galaxies in the Observable Universe.   So, that is 200,000,000,000,000,000.
  ( 2 * 10^17 stars).  Half of these stars have at least one planet.
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------------------  2107  -  Planets outside our own
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-  Our Solar System has 8 planets.  When I was in high school we had 9 planets.  Pluto got demoted to a dwarf planet.  This happened because astronomers discovered planet size asteroids larger than Pluto further from the Sun.  These outliers were named dwarf planets so Pluto had to be included.  In fact the largest asteroid orbiting between Mars and Jupiter named Ceres also became a dwarf planet.
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-  We no sooner got our own solar system redefined when we discovered other solar systems outside our own.  The first was a pulsar discovered in 1992.  This rotating neutron star crested a beam of radiation that swept across Earth like a light house beam.  The radio frequency of the beam shifted in wavelength in a cycle of repeating period.  The conclusion was that a planet , or planets, were orbiting this star causing it to wobble back and forth as the planet circles.
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-  Our Sun does the same thing as our planets orbit it.  The biggest contributor being massive Jupiter. 
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-  Then in 1995 a planet , or planets, were discovered orbiting a star called 51Pegasi.  This was a normal, main sequence star similar to our Sun.   This planet was half the mass of Jupiter and completed each orbit in 4 days. 
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-  Over the next decade thousands of exoplanets, as they are called, have been discovered.  The discoveries used two methods to confirm the star had orbiting planets.  The first was the "radial velocity method".  This uses the Doppler shift in frequency of light as the star's motion repeated  back and forth as it was pulled by the orbiting planet.  The planets are invisible to our telescopes, but, their presence is learned by their effect on their host star. 
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-  In 1999 the second method of planet discovery used the detectable slight dip in the star's light as the planet passed in front of the star,  called the "transit method".  This method only works when the plane of orbit lines up with Earth's line of sight.  
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-  To date, 2018, there have been thousands of discoveries and 1,284 of these have been "confirmed" as orbiting planets.  Confirmation requires multiple measurements of multiple orbits before astronomers can say for sure that is a planet. 
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-  Beginning in 1999 the detection of the first spectrum of light passing through the planet's atmosphere became possible.  This allowed elements to be identified, sodium being the first element found.   Scores of exoplanets have had spectra of their atmospheres analyzed.  Brightness and size and atmosphere compositions have allowed astronomers to select those  targets that are most earthlike.  
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-  In 2009  the Kepler Space Telescope was launched to add to the exoplanet study.  Kepler's telescope stared at tens of thousands of stars  all at once, watching for transits that dimmed their starlight as the planet passed in its orbit.  Thousands of these planet candidates were discovered.  Long term studies are needed for each candidate are required before a confirmations can be made. 
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-  Planet temperatures are measured.  Their mass calculated.  Chemical compositions are measured.  All to better understand how solar systems come to be and how they evolve.  We now know that tiny planets around small stars are common place. 
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-  Back to our closest star, Proxima Centura, seven temperate, rocky planets have been identified and three of these are in the habitable zone of orbits.  The total number of diverse planets is confounding, and amazing, generating much more to learn.
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-  OTHER  REVIEWS  AVAILABLE  TO  LEARN ABOUT  EXOPLANETS:
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-   2064  -  Of the 3,700 exoplanets discovered 17 are earth masses about the size of Neptune.   We can determine the planet's mass using the Doppler effect on the planet's star.  Planets can receive their water from comets and asteroids over their lifetimes in habitable zones.  Water rich planets and moons are frequent in other planetary systems. 
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-   2043   -  Evidence is that planetary systems are highly chaotic.  The chaos erases all the evidence of how they were formed.  As the technology and techniques improve more and smaller planets will be discovered.  Astronomically speaking there is total diversity in the universe.
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-  2036.  -   Is there life on other planets?   Studying 150,000 stars astronomers
have found over 4,000 exoplanets.
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-  2030. -  New data on Cepheid Variable stars in our Milky Way Galaxy find them 10 times further away.   New calculations for an expanding universe are that the expansion rate is 50,000 miles per hour for every lightyears distance. 
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-  The Hubble Constant is a measurement of how fast the Universe is expanding. For every star there is a 50% chance there is at least one planet orbiting it. If we discover a planet with a large amount of oxygen in its atmosphere there must be living organisms living there.
-   1912.  -   Our nearest star system , Proxima Centura , has at least 2 planets in orbit. One in the habitable zone, Exoplanet Proxima b. It is only 25 trillion miles away. The star Proxima has at least one planet in orbit that could likely have liquid water on its surface.
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-  1874   -   Exoplanets have moons and they may even be more habitable?  4,000 planets discovered so far but who knows how many moons?   Jupiter’s has 67 moons and two of them could support life because liquid water is below their surface.
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This same Review has an appendix listing five more reviews about Europa, three reviews about Enceladus, and five reviews about Titan. 
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-  1833. -  Exoplanets are starting to review their secrets. 
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-  1669.  -  How many planets are there?  How we do the math to determine the mass of each planet.
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-  There are 300,000,000,000 stars in our galaxy.

-  There are 2 trillion galaxies in the Observable Universe.

-  So, that is 200,000,000,000,000,000.   ( 2 * 10^17 stars )

-  Half of these stars have at least one planet.
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-  Think about it!
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-  September 28, 2018
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 ---------------------   Friday, September 28, 2018   -------------------------
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