- Attachment: Mercury
- Already astronomers have concluded that the surface composition is much different than their theories had predicted. Another surprise is that the planet’s magnetic field does not line up with the equator. Still more amazing is the possibility that they have found water ice at the bottom of the deep polar craters.
- The spacecraft has an elliptical orbit getting to within 124 miles of the surface and extending out to 9,440 miles. A complete orbit takes 12 hours.
- Mercury’s noontime temperatures reach 800 degrees Fahrenheit. So, how could an water not be vaporized? Unlike the Earth Mercury’s axis of rotation is not tilted. Its rotation is almost perfectly perpendicular as it orbits around the Sun. This means that places near the poles remain permanently in the shadows If water ice was every carried there by comets it could remain there for billions of years. ( See Review #1338 - Did comets bring water to Earth’s oceans?).
- The cameras that are exploring the surface can resolve features down to 820 feet in black and white pixels. The cameras have 11 different color filters that can separate specific wavelengths. The color mosaic created is an image with resolution of 0.6 miles per pixel. Using the wide angle cameras down to the narrow angle images they can resolve features down to 33 feet per pixel. All these images are being beamed back to Earth of astronomers to study
- The volcanism found on the surface implies a molten interior. It is the liquid core that can create the global magnetic field. So far this type dynamo has only been found on Mercury and Earth. the liquid flow between the molten iron core and the cooler inner core of solid iron beneath the mantel create an dynamo of electric current that generates a magnetic field encircling the planet. The iron core is some 60% of the mass of the planet. (For comparison the iron cores of Earth and Mars are about 30% of their mass). Either Mercury go more heavy iron from the accretion disk that was closer to the Sun, or, an early collision stripped away the outer crust of the planet. The planet is relatively small, allowing it to cool rapidly. How it maintained a molten core is another mystery.
- The composition of elements have found far more magnesium and far less aluminum than found on Earth or on the Moon. The surface has large concentrations of sodium and sulfur but low amounts of iron and titanium. The sulfur content is 10 times more abundant than on Earth. The sodium is emitted from the surface rocks creating a gaseous stream, or tail, pointing away in the direction of the Solar Wind. This is similar to what we see from orbiting comets.
- Next, the ratio of potassium to thorium on Mercury is higher that any of the other rocky planets Potassium is a volatile element and vaporizes at low temperatures. thorium is non-volatile and vaporizes at very high temperatures. Mercury is a hot planet being so close to the Sun so astronomers expected a very low ratio. Not so? Why?
- Previous theories about Mercury’s planet formation are dropping like flies as the data comes in. Mercury was blasted by the Sun that boiled off its outer layers ….( not so!). Mercury was never like the Earth because it formed is a different part of the accretion disk …( ruled out!). Mercury stared out with more mass but suffered an enormous collision with another body leaving on oversized iron core …( not totally a match but not ruled out either ).
- At one point in Mercury’s evolution a giant meteor struck the “ Caloris Basin” . At a spot exactly on the opposite side of the planet is “Weird Terrain” which reflects the result of the shockwave that passed directly through planet to the other side.
- The Sun’s gravity is 10 times greater on Mercury than on Earth. Mercury has an 88 day orbit ( its year ) and a 58.6 day rotation ( its day ). This combination gives Mercury a
“3 : 2” resonance orbit ( 3 * 58.6 = 176, 2 * 88 = 176 ). Mercury’s orbit is not circular but highly elliptical varying from 28.5 million miles radius to 43 million miles radius. Therefore, in 88 days the Sun’s energy on the surface varies from 6 times Earth’s to 14 times Earth’s .
- Mercury’s orbit from our perspective varies from 18 degrees above the Sun to 27 degrees above the Sun. Its brightness magnitude varies from 5.1 M to -2.4 M. ( 1.0 M is the brightness magnitude of the star Sirius. The more positive numbers are dimmer magnitudes. ).
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(1) www.messenger.jhuapl.edu
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707-536-3272, Friday, December 2, 2011
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