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- 2043 - Discovering planets around other stars is a big deal. It opens a whole new realm in astronomy and the evolution of life on Earth Over 4,000 of these exoplanets have been discovered to date. Astronomers can not now start with a star disk system and begin to predict what kind of planetary system will evolve. Evidence is that planetary systems are highly chaotic. The chaos erases all the evidence of how they formed.
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----------------------------------- Discovering Planets
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Discovering planets around other stars is a big deal. It opens a whole new realm in astronomy and the evolution of life on Earth Over 4,000 of these exoplanets have been discovered to date. The first discovery was in 1990 with a planet orbiting a pulsar. This was totally unexpected. Then several Jupiter size planets were discovered orbiting very close to their star
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Obviously large planets in close orbits are the easiest to find. Multiple orbits are needed to be sure you are really studying an orbiting planet and not some other object. And, large planets block more of their host’s star light. And, large planets wobble their host stars light wavelength. This is how planets are discovered ! (See footnote 1)
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As the technology and techniques improved more and smaller planets were found. What we expected was that rocky earth-size planets would be closer to their star and gaseous giant planets would be orbiting further out. Modeled after our solar system. After many discoveries the result is that there is no “typical” solar system. They are all different.
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Hot Jupiter’s in tight orbits are 1% of those found. Warm Jupiter’s in 5 to 10% of the cases with elongated orbits 0.3 to 3 astronomical units from their star. (An astronomical unit is the Earth - Sun distance , 93 million miles). 50% are super-earth’s often in multiple-planet systems. Most are orbiting close to their star not farther out like in our system. Only about 3% are orbiting at distances similar to our Jupiter and Saturn.
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Planet formation systems that we understand cannot explain this diversity and range of solar systems. There remains a deep mystery in this complexity. How planets gravitationally interact? How they shift between circular and elongated orbits? How they migrate into different orbits?
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Planetary disks range from 1 to 10% of their host stars mass. They vary considerably in gas to dust ratios and chemical composition. Astronomers still believe that planets build up through smaller collisions to become rocky planets. The giant ice and gas planets evolve further out. Their large mass collecting more of the gas and dust orbiting around them.
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Big unknowns arise from perturbations created by stars passing nearby to the system. Or, supernovae explosions disturbing a new born system. Planets migrate into different orbits and can become locked into gravitational resonance with each other. Also, planetary pinball can occur resetting an entire system.
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About half of the planets have highly elongated or inclined orbits. Some even orbit their stars the wrong way. Neptune’s 3:2 resonance with Pluto is clear evidence that migrations also occurred in our system. Both Neptune and the Kuiper Belt Objects likely formed closer to the Sun. Gravitational interactions with the four giant planets likely drove Neptune into the Kuiper Belt out to the longer orbits and scattering these KBOs
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Astronomers can not now start with a star disk system and begin to predict what kind of planetary system will evolve. Evidence is that planetary systems are highly chaotic. The chaos erases all the evidence of how they formed.
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What is our recipe for planetary formation? First off it is somehow order out of chaos. We have a model for our situation, but, recognize it is the only one we know. We do not know if this repeats itself throughout the universe. It starts with a gravitationally shrinking cloud of gas and dust floating in outer space.
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The gas collapses into clumps of matter. It’s rotation flattens into a disk. Flecks of dust and molecules smash into each other. They collect more mass and thus more gravity. This attracts more gas and dust. The whole cycle snowballs and small planets, big planets, asteroids and comets orbiting a mammoth mass that condenses into a fusion machine that lights up a planetary system. The four rocky planets orbit closer to their star. The large gaseous planets orbit farther out protecting the inner planets from asteroids and debris. This is our home in the universe.
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Maybe life is rare? Maybe it isn’t? But, habitable environments that Earth-like life could tolerate is not rare. The odds are that life conditions are common.
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Astronomically speaking there is total diversity in the universe. No two stars are alike. No two planetary systems are alike. No two planets are alike. Somehow out of the chaos some order evolves. Some life forms survive. The dinosaurs did not survive the changes chaos continued to bring. But, somehow some mammals did. You can thank your lucky stars. God only knows. If all this order did not survive just right you would not be reading this.
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FOOTNOTE: (1) How planet Kepler 186f was discovered:
When the planet passes in front of its star the dip in brightness is measured to be 0.042%
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The cross sectional area of the star is measured to be 416 million square kilometers.
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The cross sectional area of the planet must be:
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--------------------- Ap = 416 * 0.00042 = 174,720,000 km^2
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------------------ Ap = pi * r^2
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------------------ r^2 = 55,615,103
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------------------ r = 7,460 kilometers
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----------------- r = 4,645 miles
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-OTHER REVIEWS AVAILABLE ON THE TOPIC:
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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. The Kepler data is that there is a 50% chance star would have at least one planet in orbit.
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1912. - Our nearest star system , Proxima Centura , has at least 2 planets in orbit. One in the habitable zone.
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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 Review’ appendix lists 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 do we do the math to determine the mass of each planet.
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------------------------- Thursday, March 22, 2018 --------------------------------
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