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- Mercury is the closest planet to the Sun relatively near Earth at 50 million miles. Mercury averaging 34 million miles from the Sun. The Earth is 93 million miles from the Sun.
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- It took a spacecraft, named “ Messenger” 6 years to reach Mercury and it has been orbiting that planet for 4 years, starting March 18, 2011.
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- The data collected has given astronomers compelling evidence that Mercury harbors an abundance of frozen water. How can that be on a planet that experiences temperatures in excess of + 570 degrees Fahrenheit?
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- The answer lies in the fact that there are polar regions that contain craters continuously in the shadows and shielded from the Sun’ s rays. The amount of water in these craters is large, an area the size of the state of Washington and ice that is 2 miles thick.
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- There are dark layers covering the ice that likely contain organic compounds.
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- Most likely this water was delivered to Mercury by comets and asteroids in the early formation of the Solar System. Early, but late enough for water to remain.
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- Orbiting space around Mercury involved a technological challenge. The instruments in the spacecraft needed shadows as well in order to survive the intense Sun radiation. The spacecraft carried a highly reflective ceramic cloth that was unfurled as a sunshade. The sunlit side of the shade was + 570 F, the shadow side only +68F.
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- With its instruments well shaded here is some of the data results Messenger collected:
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- Mercury the closest planet to the Sun is the smallest terrestrial planet, the densest, has the oldest surface, and the largest daily variation in temperature.
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---------------------------- The density of Earth is 5,514 kg/m^2
---------------------------- The density of Mercury is 4,243 kg/m^3
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---------------------------- The diameter of Earth is 7,927 miles
---------------------------- The diameter of Mercury is 3,000 miles.
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- We can say that Mercury is the densest planet only after correcting for the added density caused by compression of the weight above its diameter compared to Earth’s. The diameter of Earth is 2 ½ times greater and that added weigh increase its average density by mere compression. The Earth being 18 times more massive.
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- Mercury’s density implies that it has a solid metal rich core that is at least 60% of the planets total mass. ( See review 1479 for the math in this calculation)
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- A surprise discovery was that Mercury has a magnetic field similar to the Earth’s magnetic field only 10% as strong. Mars and Venus have not magnetic fields. This anomaly poses some unanswered questions as to the evolution of magnetic cores in terrestrial planets.
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- Mercury has virtually no atmosphere. Its surface is as dark as an asphalt parking lot.
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- Mercury spins 3 times with 2 rotations around the Sun. A year is 88 days. A “ day” is 58.6 days. Because Mercury’s orbit is so elongated the Sun’s radiation varies by 200% during the 88 day year. The total range of temperature variation is over 1,100 F, from
-325F to +860F.
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- Mercury’s orbit varies from 25.5 million miles to 43 million miles.
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- Our Moon is 2,159 miles diameter. Mercury is only slightly larger at 3,000 miles diameter. There are two other moons in the Solar System that are larger than the planet Mercury, Ganymede and Titan.
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- Because Mercury is much smaller it actually cooed down 2 ½ times faster that Earth cooled in its formation ( See Review #1479) All volcanic activity ceased after 1 billion years. Earth is 4.5 billion years old and still has volcanic activity.
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- Review #1479 also calculates the size of the core and the size of the crust of Mercury. Core radius is 1,217 miles, crust thickness is 289 miles.
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- See Review #1478 for the calculation of Mercury mass being 3.3*10^23 kilograms. Just 5.5% the mass of the Earth.
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- The calculations for Mercury’s average temperature is Review #`1369 resulted in +325 degrees Fahrenheit.
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- Reviews #1343 and #1165 tells about the surface composition of Mercury and what it means for its possible evolution.
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- Review #815 tells about the spacecraft and its launch August 3, 2004.
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- Review #44 compares Mercury’s specification to that of Venus , Earth, and Mars.
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- The last maneuver of the Messenger Spacecraft occurred Friday, April 24, 2015. All of its helium gas propellant is gone. Mercury’s gravity will bring Messenger down to crash into the surface at 8,750 miles per hour.
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- Stay tuned, for a mission results visiting the “Dwarf” Planet Pluto.
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- Request other reviews if interested: 1706,1479, 1478, 1369, 1165, 815, 44
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----- 707-536-3272 ---------------------- Friday, April 24, 2015 -----
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