ASTR Chapter 8 Part 2
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This 3 page Class Notes was uploaded by Wesley Fowler on Thursday April 14, 2016. The Class Notes belongs to ASTR 151 001 at a university taught by Dr. Sean Lindsay in Spring 2016. Since its upload, it has received 16 views.
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Date Created: 04/14/16
Wesley Fowler ASTR Chapter 8 Introduction to Mercury Distance from Sun: 0.4 AU Radius: 2,440 km (slightly larger than the Moon) 23 Mass: 3.3 x 10 kg 3 Average Density: 5,400 kg/m (Very high) Orbital Period: 88.0 days Rotational Period: 58.6 days Axial Tilt: 0.034 - (Don’t need to memorize these) Has an extreme variation in temperature due to lack of atmosphere and very long Solar Days Does have a magnetic field Does not have a permanent atmosphere Mercury’s Orbit Mercury has the highest eccentricity of all the planets Mercury always appears close to the sun when observed from Earth. It’s very hard to observe. Mercury, unlike the moon, does not have a synchronous orbit. Its orbital period is 88 days while its rotational period is 58.6 days. - This was discovered via sending radio pulses and analyzing them with the Doppler Effect Mercury is tidally locked even though its orbit is not synchronous. For every two orbits around the sun, mercury rotates three times. Thus, Mercury has a 3:2 spin-orbit resonance (ratio of relating periods) - The Moon has a 1:1 spin-orbit resonance This is caused by the tidal force between the Sun and Mercury. - 17x stronger than the force between the Sun and Earth - Tidal bulge aligns with perihelion and aphelion in 3:2 ratio 3:2 spin-orbit ration gives Mercury a solar day of 176 days, which is two Mercury years. The solar day is very strange on Mercury. The Sun rises in the east, goes back east and sets, then rises again to eventually set in the west. Mercury’s Surface Has a highly cratered surface that are less densely packed than the Moon’s surface. - Has gently rolling intercrater plains that cover 40% of the surface. The oldest surface. Scarps/Rupes: Very long and high cliffs that stretch across the surface - Named after ships - Formed from the planet’s shrinkage Hollows: Deep pits with very steep walls that occur inside or near crater rims and floors. Most likely caused by being so close to the sun, solar erosion. - Unique to Mercury. Caloris Basin: 1400 km basin thought to be caused by an impact. Ringed by mountains 3 km high - Weird Terrain: Rippled territory on the opposite side of the impact zone, most likely caused by the shockwave from the impact. Just like the Moon, Mercury has permanently shadowed craters craters at the poles, which most likely contain water ice. Mercury’s Interior - Extraordinarily large iron core: 2100 km (~80% of diameter) - Thin and iron-poor mantle and crust: Top 400km Rotational inertia indicates an iron- sulfide layer outside the liquid iron core. Evolution of Mercury 1. After forming, Mercury melted and separated into layers. 2. Cooled down slower than the Moon, and thus has a thinner crust. This lead to molten flooding, and the formation of intercrater plains 3. Mercury shrank as it cooled, causing Scarps/Rupes to form across the surface.
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