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- 1692 - The Rosetta spacecraft landed an instrument package on Comet 67P. This review is some background while waiting for the science news to arrive. A math lesson estimates the size of the comet.
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--------------------------- 1692 - Rosetta Mission lands on the Comet.
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- European Space Agency has put a satellite in orbit around Comet 67P and dropped a Lander instrument package on the surface. ( August 13, 2014 )
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- Rosetta is the spacecraft.
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- Philae is the Lander.
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- I am anxiously waiting for information to be released on what science is learning about the comet. This review is premature but good background about what we already know.
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- The comet was first discovered in 1969. Its orbital period around the Sun is 6.45 years. Its elongated orbit travels 186 million miles from the Sun to 500 million miles from the Sun between the orbits of Mars and Jupiter. The Earth is 93 million miles from the Sun. The comet is traveling 84,000 miles per hour.
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- The comet is closest to the Sun on August, 2015. The Rosetta spacecraft arrived to orbit the comet August, 2014 after a 10 year journey. Launched March, 2004 it traveled 2,860 million miles to get to the comet because it had to sling shot around Earth and Mars to gain the speed needed to catch up with the comet. It could not carry enough fuel to fly straight there.
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- When the spacecraft got within 175 miles away it took a picture. The comet rotates every 12.4 hours. With a good broadside image the picture represented 5 kilometers across having a dumbbell shape or two connected spheres.
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- To estimate how big the comet is draw two circles on the picture to represent the two spheres. Use ratios to estimate the diameter of the two spheres. The larger sphere has a radius of 1200 meters. The smaller sphere radius is 840 meters.
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- Picture is 6.1 inches across, represents 5,000 meters.
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- Large sphere diameter is 2.94 inches. 2.94 inches / 6.1 inches = x / 5000 meters
- x = 2400 meters. Radius = 1200 meters.
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- Small sphere diameter is 2.05 inches. 2.05 / 6.1 = x / 5000 x = 1680 meters
- Radius = 840 meters.
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- Volume = 4.3 * pi * R^3
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- Large sphere volume = 1.3 * 3.14 * ( 1200)^3 = 7000 million cubic meters
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- Small sphere volume = 1.3 * 3.14 * (840)^3 = 2400 million cubic meters.
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- Estimating the average density of the comet to be 300 kilograms per cubic meter. (water is 1000 km/m^3 ).
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- Total volume is 9400 million cubic meters
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- Mass = density * volume
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- Mass = 300 kg / m^3 * 9.4 * 10^9 m^3 = 2.8*10^12 kilograms
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- 1 ton - 1000 kilograms
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- Mass = 2.8 billion tons.
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- An oil tanker weighs about 0.2 billion tons. So, this comet is the size of 14 oil tankers.
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- The picture shows the Atlanta Airport runway next to the comet for size comparisons. The runway is 725 meters, ( 0.45 miles ) So, the comet is about 6 airport runways long. The comet is 2.7 miles long by 2.5 miles wide.
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- The escape velocity for that size mass is 3 feet per second, that is about 2 miles per hour. You can see why Philae Lander bounced when it landed. The temperature of the comet that far from the Sun is - 60 C. The orbit of the comet gets to its closest point to the Sun on August 13, 2015. It should warm up and outgas a tail by then. The last time the comet made that loop was August 18, 2002.
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- The mission is costing ESA 1.5 billion Euros. The mission was named after the Rosetta Stone discovered in Egypt in 1749. The Lander was named Philae after an island in the Nile where an obelisk was found that helped archeologists decipher the hieroglyphics written on the Rosetta Stone.
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- More science to come. More reviews to come, stay tuned.
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RSVP, with comments, suggestions, corrections. Index of reviews available ---
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