- We have 8 planets in our Solar System. There may have been more orbiting our Sun at one time and maybe a few escaped during the chaos of planetary evolution. Some may have just been far outside in the Kuiper Belt and the Sun’s gravity just let go of them.
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- We lost Pluto by committee. A group of astronomers decided Pluto could no longer be a planet in our Solar System. It now must be referred to as a Dwarf Planet in the Kuiper Belt of comets. The reason is that there were bigger Dwarf Planets further out in orbit around the Sun than Pluto. We either had to call them planets too or demote Pluto to a Dwarf.
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- But, what happens to planets that do loose contact with their star. If a planet looses gravitational contact with its star its velocity and momentum carries it off to freely float in space. There is lots of space out there. It is not as if planets would be bumping into each other. Are there planets drifting freely in free space? Astronomers think there are.
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- There is strong evidence that hundreds of billions of these free-floating planets, un-tethered for any star, are wandering through the Milky Way Galaxy. Un-tethered planets are the natural result of the inevitable chaotic gravitational interactions that evolve in every solar system.
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- Surveys suggest that there are twice as many rogue planets as there are stars in the galaxy. Planets are far easier to make than they are to keep. Solar systems often become unstable with planets flung out of their orbits and place of birth.
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- These rogue planets are being detected using a technique called “ micro-lensing. When telescopes focus on a particular star using very sensitive light meters and an unbound planet passes in front of the star the micro gravitational lensing temporarily increases the brightness of the background light source star. By determining the peak brightness from two different perspectives, an Earth telescope and a space telescope, astronomers can determine how far away the planet is. The duration of the brightening correlates with the mass of the planet that is acting as a lens.
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- A Jupiter- size planet will create a micro-lens brightening that last less than 2 days. A Brown Dwarf star would micro-lens brightness for weeks. The height of the brightening light curve tells astronomers how on-target the alignment is between the light source, the planet lens, and the observations from Earth. A perfect alignment will create a circular brightening ring called the Einstein Ring, which was predicted by Einstein in his General Theory of Relativity.
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- Micro-lensing events are rare because they rely on a chance alignment of a background star and a passing planet. Astronomers must monitor a large number of stars over a longer period of time in order to find this transient stellar brightening event.
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- However, astronomers have surveyed the brightness of 50,000,000 stars over 2 years. They have detected 474 microlensing events. 10 of these lasted less than 2 days indicating a Jupiter-size planet. Their analysis suggests that 75% of new objects detected are floating freely through space. You would think these would be cold, dark, rocks, or gas not suitable for any life. Astounding predictions are that blanketed by a thick hydrogen atmosphere and warmed by radioactivity and geothermal sources these rogue planets could support life.
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- Objects larger than planets but too small to become stars are called Brown Dwarfs. 100’s of these Brown Dwarfs have been found in the Galaxy. They have been classified into 3 types: “L” Dwarf stars have surface temperatures of 2,600 F. They are not massive enough to have enough gravity, to have enough pressure, to have a high enough temperature, to start hydrogen fusion into helium. Our Sun’s surface temperature is 8,000F. “T” Dwarf stars are cooler, 1,700 F. “Y” Dwarf star are the coolest, < 350 F and some have been found as cool as 80 F.
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- An announcement will be made shortly , stay tuned.
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707-536-3272, Tuesday, June 5, 2012
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