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Lecture 17

AS101 Lecture 17

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Department
Astronomy
Course
AS101
Professor
Patrick Mc Graw
Semester
Winter

Description
Lecture 17 4/10/2013 12:46:00 PM Mars Clarifications:  Venus is the object in the solar system with the thickest atmosphere, excluding the Jovian planets. Clarifications: Densities of Planets:  When trying to figure out a planet's composition based on its density, we need to take into account the fact that planets are compressed by their own gravity (especially near the center.)  Earth, for example, would be much less dense if you could disassemble it.  In the back of your textbook are “celestial profiles” for each planet. Both a density and an “uncompressed density” are listed.  Uncompressed density means a calculation of what the density would be if the planet were not compressed by its gravity.  Large objects are compressed more than small objects. Mars:  Distance from Sun: 1.5 au  Diameter: 6790km (0.53 of Earth's)  Orbital Period: 687 days  Rotation period: 24.6 hours  Average Surface Temp: -63C  Atmosphere: o 95% carbon dioxide o Much thinner than Earth's: less than 1% of the density.  Mars’s moons: Phobos and Deimos: o Small and irregularly shaped (less than 30km across) o May be captured asteroids: composition appears to be different from the planet.  History of explanation: o First successful flyby: Mariner 4, 1965 o First landings: Mars 2+3, 1971 o Viking 1+2, 1975 o About 40 missions so far o Currently Active: Curiosity rover (more about this later)  Water on mars: o Very little water vapour in the atmosphere, and liquid water cannot exist on the surface because of the low pressure. o But ice exists a short distance below the surface, o Very little water vapour in the atmosphere, and liquid water cannot exist on the surface because of the low pressure. o But ice exists a short distance below the surface, and polar ice caps consist of a mixture of water ice and frozen carbon dioxide (dry ice). o Surface features resembling water erosion on Earth, along with microscopic features in some rocks, suggest that there was liquid water earlier in the planet's history.  Life on mars? o No sign of it now. o Could there have been life earlier, when there was liquid water? o So far, no clear evidence of it. o In 1996, a paper in Science by David MacKay suggested that a meteorite believed to be from Mars contained evidence of fossilized bacteria, but this interpretation remains controversial.  Mars Curiosity Rover: o Launched Nov. 26, 2011, landed Aug. 6, 2012 o About the size of a car. o Goals include looking for evidence of present or past life. o Carries multiple cameras, a drill, laser “drills,” miniature laboratories to analy
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