Lecture 19 iscuss Quiz Mercury Venus Outline Outline For Rest of Semester Oct. 29 th hapter 9 (Earth) Nov 3 rd and 5 th hapter 9 and hapter 10 (Earth and Moon) Nov. 10 th and 12 th hapter 11 (Mars, Venus, and Mercury) Nov. 17 th and 19 th hapter 12 (Jupiter and Saturn) Nov 24 th hapter 13 (Uranus and Neptune) Nov 26 th Thanksgiving ec. 1 st - Exam 3 ec. 3 rd hapter 14 (Pluto, and the Kuiper elt) ec. 8 th and 10 th hapter 7 and 8 (omparative Planetology I and II) Tuesday ecember 15 th (7:30 am 10:15 am) Final Exam No Reading days are scheduled this semester Exam Period begins at 7:30 a.m. on Monday, ecember 14 and ends on ecember 21 Mercury 1
Observations Observing Mercury What are best conditions to observe? raters How similar to the moon How different Unexpected magnetic field Why unexpected How measured Observations Observing Mercury What are best conditions to observe raters How similar to the moon How different Unexpected magnetic field Why unexpected How measured No-name rotation 2
The Moon s rotation always keeps the same face toward the Earth due to synchronous rotation synchronous rotation 1-to-1 spin-orbit coupling raw ball and arrow at,,, raw ball and arrow at,,, few days later Mercury s orbital period is 88 days Mercury s rotation period is 58 days Mercury s orbital period is 88 days Mercury s rotation period is 58 days 3
raw ball and arrow at,,, raw ball and arrow at,,, First move into position in orbit. Then rotate around Mercury s axis. Mercury s orbital period is 88 days Mercury s rotation period is 58 days 88/4 = 22 days to get to 22/58 = 0.375 88/4 = 22 days to get to Mercury s orbital period is 88 days Mercury s rotation period is 58.6 days 22/58 = 0.375 raw ball and arrow at,,, raw ball and arrow at,,, 0.375 of a full turn Mercury s orbital period is 88 days Mercury s rotation period is 58 days 88/4 = 22 days to get to 22/58 = 0.375 Mercury s orbital period is 88 days Mercury s rotation period is 58 days 88/4 = 22 days to get to 22/58 = 0.375 4
Planet s orbital period is 90 days Planet s rotation period is 60 days Planet s orbital period is 200 days Planet s rotation period is 200 days (retrograde) nimation 5
?? Observations Observing Mercury What are best conditions to observe raters How similar to the moon How different Unexpected magnetic field Why unexpected How measured 6
Heavily cratered surface Less dense cratering than moon Gently rolling plains Scarps No evidence of tectonics Note how much more densely the craters occur on the moon s surface. Scarps are cliffs nimation This one is more than a km high They probably formed as the planet cooled and shrank 7
The aloris asin is evidence of a large impact The seismic waves from the impact that caused the aloris asin caused this deformation on the opposite side of Mercury Observations Observing Mercury What are best conditions to observe raters How similar to the moon How different Unexpected magnetic field Why unexpected How measured Questions It is relatively difficult to observe details on the surface of Mercury from Earth because ) detail is obscured by bright glows from hot regions of molten surface heated by the intense sunlight. ) its orbit always keeps it on the opposite side of the Sun from Earth. ) it is a small object that always appears close to the Sun in the sky. ) its surface is always completely covered in clouds. 8
Questions The reason the temperature on the dark side of Mercury is warmer than originally expected is that ) Mercury's large iron core conducts heat through the planet. ) Mercury does not rotate synchronously with its orbital period. ) several very active volcanoes on Mercury, produced by tidal stresses from the Sun, produce excess heat. ) winds in Mercury's tenuous atmosphere carry heat from the daytime side to the night side. Questions What is believed to be the cause of the long, meandering scarps (cliffs) observed on Mercury? ) shrinkage of the planet as Mercury cooled ) large impacts near the end of the early period of heavy bombardment ) volcanic eruptions along crustal faults over hot spots in the mantle ) crustal movement due to convection in the mantle, similar to continental drift on Earth but to a much smaller extent iscuss Quiz Mercury Venus Mars Outline For Today Interesting facts Mariner 2 visited in 1962 Venus Express recently arrived 9
Observations Observing Venus What are best conditions to observe? raters How similar to the moon How different Unexpected magnetic field Why unexpected How measured Observations Observing Venus What are best conditions to observe? limate Runaway greenhouse effect Surface 10
Venus s rotation is slow and retrograde ( retro ) No-name rotation 1.125 turns 1.5 turns 0.375 of a turn 0.75 of a full turn synchronous rotation Mercury s orbital period is 88 days Mercury s rotation period is 58 days 88/4 = 22 days to get to 11
How long is Venus s day? Venus s orbital period is 224 days Venus s rotation period is 243 days (retrograde) raw ball and arrow at,,, Observations Observing Venus What are best conditions to observe? Surface limate Runaway greenhouse effect The surface of Venus shows no evidence of plate tectonics The surface of Venus is surprisingly flat, mostly covered with gently rolling hills There are a few major highlands and several large volcanoes The surface of Venus shows no evidence of the motion of large crustal plates, which plays a major role in shaping the Earth s surface 12
Volcanic eruptions are probably responsible for Venus s clouds Venus s clouds consist of droplets of concentrated sulfuric acid ctive volcanoes on Venus may be a continual source of this sulfurous material 13
Observations Observing Venus What are best conditions to observe? Surface limate Runaway greenhouse effect limate on Venus followed a different evolutionary path from that on Earth Venus s high temperature is caused by the greenhouse effect, as the dense carbon dioxide atmosphere traps and retains energy from sunlight. The early atmosphere of Venus contained substantial amounts of water vapor This caused a runaway greenhouse effect that evaporated Venus s oceans and drove carbon dioxide out of the rocks and into the atmosphere limate on Venus followed a different evolutionary path from that on Earth Runaway Greenhouse Effect lmost all of the water vapor was eventually lost by the action of ultraviolet radiation on the upper atmosphere. The Earth has roughly as much carbon dioxide as Venus, but it has been dissolved in the Earth s oceans and chemically bound into its rocks 14