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- What are these? In history , Vesta is the Roman goddess of health. Ceres is the Roman goddess of agriculture. And Phoebe is a great Titan t,he daughter of Uranus. In astronomy, Vesta is the third largest asteroid. Ceres is the largest asteroid. now called a dwarf planet. Phoebe is a one of the 30 moons that orbit the planet Saturn.
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-. Vesta and Ceres are the two of the largest asteroids in the Asteroid Belt between Mars and Jupiter. Phoebe is one of the 30 variety of moons orbiting the planet Saturn. Titan is the most famous moon of Saturn and is the third largest moon in the Solar System. Titan is 3,200 miles in diameter. Phoebe is much smaller with 132 mile diameter
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-. Phoebe is strange for an moon this size to be perfectly round. It should not have enough gravity to pull itself together. Phobe’s density is higher than the other icy moons orbiting Saturn. Phoebe is little but most almost planet-like in its structure.\. For Phoebe to be spherical it must at one time have been molten.
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-. What could have made Phoebe get hot? One possibility is that it contained radioactive elements, like aluminum-26, which has a half-life of 720,000 years. A decaying isotope, like aluminum- 26, can produce a lot of heat.
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-. Another oddity is that the many craters on Phoebe don't look like “impact craters“. These craters appear to result from internal forces ,such as escaping gases. All of these craters are “cone shaped“.
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- There is such a variety of moons orbiting Saturn that the likely did not all come from the same place. Rather than being formed with the planets accretion disk these moons are likely captured satellites.
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-. A big hint that a capture is what happened to Phoebe is that it has an retrograde orbit. It is orbiting in the opposite directions of Saturn's rotation. It's orbit is more eccentric than circular covering 16,000,000 miles in diameter.
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-. A spectrograph of Phoebe’s surface detects complex hydrocarbons that are normally found outside of the orbit of Neptune, inside the Kuiper belt of comets.
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-. For Saturn to capture Phoebe coming in from the Kuiper belt a 3rd object is necessary. If a 3rd object were ejected the lost energy may have slowed Phoebe enough to allow it to be captured by Saturn as it went by.
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- Phoebe has a story to tell and we are still learning what it is.
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- All that is the Solar System today evolved from a collapsing disk of gas and dust spinning around the Sun. Collisions and gravity formed the planets. The left over debris includes the asteroids and the comets. They extend out to the Oort Cloud that is more than one light year from the Sun.
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--. The Solar System is full of these large objects that are not quite planets.
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-. NASA with the Dawn space spacecraft has visited one of the objects, Vesta, and will soon visit the second object, Ceres.
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-. Vesta is 326 miles wide but has mountains that are 14 miles high and craters deeper than any that are on Earth. Vesta is a dry wasteland with many impacts and long ago gone oceans of magma. Vesta is water poor. It is one of the brightest asteroids with the magnitude of +5.4. It can easily be seen with binoculars. It is potato shaped orbiting the Sun in 3.63 years at 2.3 astronomical units radius.
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- Despite being dry Vesta has compounds found in water molecules on its surface and it has underground ice. Vesta has deep craters are the result of massive collisions. Meteorites that have rained down on earth had the same composition that likely came from Vesta.
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-. Ceres is 590 miles diameter which is 33% the diameter the Moon. It was recently named as a Dwarf Planet. Ceres is an icy primitive sphere. The two could not be more different. Ceres is water rich. It was the 5th planet in our Solar System for 49 years. First discovered in 1801. Ceres’ orbit takes 4.6 years and is 2.77 astronomical units from the Sun. The icy mantle is 37 to 75 miles thick and contains more freshwater than all of that on Earth. Its average temperature is -38C. Its mass is 4% that of the Sun. By diameter Vesta is 55% as large a Ceres and Ceres is 0.13% the mass of Mars.
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-. These two objects make up make up 33% of all the mass of the millions of asteroids that are in the Asteroid Belt between Mars and Jupiter.
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-. The Dawn spacecraft launched in 2007 visited Vesta to in 2011 for 14 months and is now on its way to visit Ceres.
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-. The Dawn spacecraft is scheduled to arrive at Ceres in March 2015. It will orbit for 11 months starting at 3,700 miles altitude orbiting every 68 hours. And then descending to 23 miles altitude. The two will be 260,000,000miles from the Sun. The Earth is 93,000,000 miles from the Sun.
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-. Analysis to date suggests a Ceres’ surface is water ice. It is hoped to discover liquid water beneath its icy surface. An announcement will be made shortly, stay tuned.
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See Reviews # 1618 the Dawn spacecraft visits Vesta., and, # 847 Ceres the 5th planet in our solar system.
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RSVP, with comments, suggestions, corrections. Index of reviews available ---
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