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Announcements ● ● Assignments were very good this week! Let me know this week if you’re planning to do a presentation rather than a report The Search ● An overview of the Mars Rover Mission ● Gas Giant Planets ● – Sketch of a Gas Giant – Who's who in the Outer Solar System – Formation of Gas Giants – Formation of GG moons – Tidal Forces – Visits to the Planets How Unique is Earth? The Mars Rovers ● ● ● ● Identical pairs of rovers sent to opposite sides of Mars Spirit and Opportunity Each has a 12:20 `day' (sol) ; since on opposite sides of Mars, it is always day for one of the two Primarily geology mission. The Mars Rovers ● Launched in June/July 2003 ● 3 Stages: – Get off out Earth's surface – Get out out Earth's orbit – Head towards Mars The Mars Rovers ● ● ● ● Began landing in Jan 2004 Entered atmosphere at 12,000 mph (Chicago -> San Francisco in 9 minutes) Broke using heat shield, parachute. Took pictures on decent to gauge horizontal velocity ● Deployed airbags ● Fired retro-rockets ● Bounced a lot The Mars Rovers ● ● Once landed and stable, base unfurled Rover, which was also folded up, unfurled The Mars Rovers The Mars Rovers ● Four Science Goals: – Determine whether Life ever arose on Mars – Characterize the Climate of Mars – Characterize the Geology of Mars – Prepare for Human Exploration The Mars Rovers ● ● ● ● ● Search, characterize rocks & soils that hold clues to past water activity and geologic process Determine distribution, composition of minerals, rocks, and soils surrounding the landing sites. Perform "ground truth" of surface observations made by orbiters Search for iron-containing minerals that indicate water Geological clues to the environmental conditions that existed when liquid water was present. Assess whether those environments were conducive to life. The Mars Rovers ● ● Cameras – Panoramic Camera (Pancam) – Microscopic Imager (MI) – Engineering cameras: Hazcams and Navcams Spectrometers – – – Miniature Thermal Emission Spectrometer (Mini-TES) Mössbauer Spectrometer (MB) Alpha Particle X-Ray Spectrometer (APXS) ● Rock Abrasion Tool (RAT) ● Magnet Array Gas Giant Planets ● Overview ● Who's Who ● Formation ● Moons ● Tidal Forces Our Solar System ● Almost all of mass of planets are in the 4 giant planets The Giants ● ● The Giants are sometimes all called `Jovian' planets after Jupiter After more exploration showed their diversity, this term lost favor The Giants ● ● ● The giant planets inhabit the outer solar system (5-30 AU) This means they get less energy from the Sun (4% 0.1%) per area Top of cloud cover of planets is very cold (-170oF --350oF) The Giants ● ● ● ● The giant planets can be weighed very accurately by measuring the speed of their moons. Much heavier than Earth, but not so heavy considering their size Densities 600 – 1600 kg/m3, compared with Earth's 5700 kg/m3 Mostly made of gas/liquids? The Birth of Giants ● ● ● ● In outer solar system, cooler Less evaporative stripping of volatile gasses If sufficiently massive cores form, can keep even volatile gasses These gasses will be representative of the very early solar system The Birth of Giants ● ● ● ● Since early solar system is largely composed of Hydrogen, so will gas giants Rocky or Icy or Slushy core High-hydrogen atmosphere has some similarities to atmosphere in Miller-Urey experiment Can form lots of organics The Birth of Giants ● ● ● Large rotating liquid metal region means large magnetic field Jupiter: Significant field extends out size of the Sun! Can seriously effect nearby objects. The Birth of Giants ● ● ● ● ● Jupiter in Infrared Large mass -> high pressure, temperature at center Temperature at center of Jupiter ~ 4 times surface of Sun! Collapse from origin of planet still slowly continuing Releases heat energy These planets have a source of heat The Birth of Giants ● ● ● ● ● Jupiter in Infrared Gas giants emit more heat than they absorb from Sun At earlier times, would have been much hotter Moons, which are nearby, heated by their nearby planet Many of these moons are large (planet-sized) Moons might be interesting for life? The Composition of Giants ● ● ● Structure of gas giant atmospheres depends on mass of planet Lower planet mass -> lower interior pressure -> may not be high-pressure enough to make hydrogen into a liquid metal. Rock/Ice cores surrounded by Hydrogen/Helium gas The Moons of Giants ● ● ● ● Planets large enough that many moons were also formed Many of them planet sized in their own right Get heat from planet Some (Io/Jupiter) effected by planets magnetic field ● Atmosphere? (Titan, Saturn) ● Water? (Europa, Jupiter) The Moons of Giants ● Formation: like planets around sun ● Rotating body, disk forms ● Moons generally along plane of rotation of planet Tidal Forces ● ● Tidal forces familiar from Earth Not due simply to gravitational attraction (that would just move the whole body) but the difference in gravitational force across the body ● Gravity: inverse square ● Tidal forces: inverse cube ● REALLY matters how close the object is Rings ● ● ● ● Most of the gas giants have rings Jupiters are very small, probably transient, and made largely of dust Too close to planet, tidal forces are strong enough to disrupt moons or prevent them from forming Result is material scattered in orbit around planet Visiting the outer Solar System ● Pioneer ● Voyager I/II ● Galileo ● Ulysses ● Cassini-Huygens Pioneer 10,11 ● ● ● ● ● Launched in 1972 Camera, equipment for measuring gas/magnetic fields in the solar system, radiation Now ghost ships Carry plaque in case ever discovered Plaque designed by Carl Sagan Voyager I/II ● ● ● ● ● Launched in 1977 Carry cameras, equipment for measuring gas/magnetic fields in the solar system Now at 90 AU (8.4 billion miles) Still send trickle of data Will continue transmitting until ~2020 (not enough sunlight to power equipment) Voyager I/II ● ● ● ● Carries a golden record Has needle, instructions on how to play it on cover Contents assembled by Carl Sagan Contains music, greetings in 55 langaguges, natural/atmospheric sounds, written greetings http://www.jpl.nasa.gov/flash/voyager_record/index.htm Voyager I/II ● ● Travelled past Jupiter, Saturn Voyager II then flew by Uranus and Neptune; Voyager I stopped by Titan (largest moon of Saturn), trajectory then sent it out of plane of galaxy Ulysses ● ● ● Sent to examine magnetic field, radiation from Sun, esp. poles Sent to Jupiter for slingshot out of plane of ecliptic Also obtained magnetic field data from Jupiter Galileo ● ● Launched 1993 Study Jupiter's atmosphere, satellites, magnetosphere for 2 years. ● Made encounters with asteroids ● Arrived at Jupiter, Dec 1995 ● ● Significantly advanced our knowledge of the Galilean moons At end of mission was burned up in Jupiter's atmosphere to avoid contaminating moons http://www.jpl.nasa.gov/videos/quicktime/galileo.qtl Galileo ● Took pictures of direct impact of comet into Jupiter in 1994 Cassini-Huygens ● ● ● Will arrive at Saturn later this year (July) Already taking pictures Will send a probe (Huygens) to Titan Planets of Interest ● Where might life be? – Gas Giants? – Moons? ● Europa Titan ● Iapetus ● Gas Giants ● Convection is a fundamental process – ● Happens everywhere Fluid heated at bottom rises, cools, falls back down ● Gas giants have hot centers ● Large-scale motions ● Mix material Gas Giants ● ● ● ● Makes it difficult to imagine life forming No real surface to live on Chemicals constantly being mixed around No originally contained environment (`protocell') Moons ● ● ● Gas giants have planet-sized moons At least one (Titan) has a significant atmosphere Another (Europa) very likely has liquid salty water under a layer of ice Europa ● ● Very suggestive it has a liquid underneath – No cratering – Many fractures, ridges on surface What would this mean for life? – If some source of energy on inside (geothermal, chemical), very real possibility of some sort of life Titan ● ● Very Cold Massive, Cold enough to have an atmosphere (1.5 x as dense as ours!) ● No oxygen ● No liquid water ● Hydrogen rich ● Interesting organic chemistry ● Lakes of hydrocarbons? ● Huygen probe 2005 Iapetus ● ● ● Moon of mystery Side facing away from Saturn is very, very dark Much less light reflected than bright side ● How did this happen? ● What is the dark material? How Unique is Earth? ● What is special about Earth? ● How important/rare are those things? ● How many such planets are there likely to be? Earth ● Atmosphere – Large surface gravity ● Reasonable temperature ● Rocky srface ● Large moon ● Lots of heavy elements How Important/Rare are these? ● Heavy elements; – Likely ubiquitous in planets around Pop I stars How Important/Rare are these? ● Rocky Surface – Can happen if there is heavy elements (see above) – Probably true of all planets close enough to have liquid water – (But planet migration) How Important/Rare are these? ● Atmosphere – Requires not too close to sun – Requires massive enough planet How Important/Rare are these? ● Reasonable Temperature – `Goldilocks zone’ – Needs to be right distance to star How Important/Rare are these? ● So we require – Rocky Planet – Of the right mass – At the right distance from the star Habitable Zone ● ● ● Corresponds to further than Venus to about Mars distance for our Sun Using inverse-square law, could calculate for other stars Main requirement: liquid water in the presence of an atmosphere. Habitable Zone: Binary Stars ● ● ● ● ● About half of all stars are in binary systems Stars orbit a common center of mass (more on that next week) Can planets have reasonable orbits in such systems? Yes, but must orbit one star or be far away from both; `Figure 8’ orbits aren’t stable Reading for Next Class (Apr 23) ● Chapter 17: The Discovery of Extra-Solar Planets – Techniques for finding planets – Results – Looking closer – Atmospheres? – PlanetQuest