PHYS 183Milky Way Inside andOutLecture 23Apr 6, 2021Prof. V. KaspiDepartment ofPhysicsMcGill SpaceInstituteThursday 10-11am or byappointment
Course Evaluations Open!•Important exercise…please take seriously!•Used for determining:•Future teaching assignments•Tenure dossiers•Salary increases•Looking for >50% response to drop 2nd lowest quiz!
Reading for this class•7.3 “Mars: A Victim of Planetary Freeze-Drying”•Ch 8: “Jovian Planet Systems”•Covering only parts of this Chapter•Ch 9: “Asteroids, Comets and Dwarf Planets”•Covering only parts of this Chapter
Today’s Class: Starting a Whirlwindtour of the Solar System•Mars•Jovianplanets•Comets
Mars•“The Red Planet”RMars= 3390 km, MMars=6.4x1023kg•Rotates every 24 hrs, 39 min•Obliquity 25 deg•Orbital period 687 days•planet has long captured ourimagination; best studied•historically because of claims of“canals”: since disproved•Has CO2ice polar caps that change inmorphology
Mars “canals”•Giovanni Schiaparelli 1877: saw “canals:”straight lines on surface•No photography•Percival Lowell late 1800’s: claims Marsinhabited by intelligent life•Canals seemed to change over years•built canals to get water from polar caps•agriculture: seeing vegetation grow seasonally??•Later realized optical illusions•Many point-like features in low-resolution telescopesjoined up to form ‘lines’•Windsàdust storms•Not seen by modern telescopes or flybys•Today we know there are no canals. Oh well.
Mars’ surface...•Mars hasvolcanoes, though probablydormant•most are in northern hemisphere:•Fewer craters in North than in South•largest isOlympus Mons:24 km!•one of several volcanoes in theTharsis riseregion, just north ofMars’ equator•VallesMarineris:giant canyon spanningboth hemispheres: 4000 km long!•rift valley:crust broke•unlike Grand Canyon: water erosion•no evidence for plate tectonicsValles MarinerisLarge volcanoesCloser View ofValles MarinerisOlympus Mons
Water was once on Mars!•Alotof evidence water once flowed:•dried up lakes and rivers, especiallyin older southern highlands•evidence for floods•evidence for water erosion of crater rimsdried upriverbedevidencefor flashflood