Astronomy Semester Exam-Things to know: Exam will consist of Chapters 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and 13. What to know for Chapters 9, 10 & 11 (Venus, Mars & Jupiter): Venus Mars Jupiter Planet order 2 4 5 Orbital period 0.62 years 1.88 years 11.9 years Semi-major axis 0.72 AU 1.52 AU 5.2 AU Mass 0.82 x Earth 0.11 x Earth 318 x Earth Radius 0.95 x Earth 0.53 x Earth 11.2 x Earth 3 3 Density 5240 kg/m 3930 kg/m 1300 kg/m3 Surface Gravity 0.91 x Earth 0.38 x Earth 2.5 x Earth Escape speed 10.4 km/s 5.0 km/s 59.5 km/s Rotational Period -243 days 1.026 days 0.41 days Inclination (axis tilt) 177.4° 23.98° 3° Surface Magnetic Field less than 0.001 x Earth 1/800 x Earth 14 x Earth Surface Temperature 730 K about 150-310 K 125 K Number of Moons 0 2 63 and counting Venus Earth's Sister Planet Observing Venus from Earth Venus never separates from the Sun by more than 47o, as viewed from the Earth o appears above the horizon before sunrise and after sunset. Extremely bright o (10 x brightest star) (reflectivity = 70%) o 3rd brightest object in the sky, next to the Sun and the Moon Venus - General Properties 2nd Planet from the Sun semi-major axis ("radius") = 0.72 AU o period = 225 days Radius = 6052 km = 0.95 REarth Mass = 4.9 x 1024 kg = 0.82 MEarth Density = 5240 kg/m3 o Radius, mass, & density are Earth-like or "sister planet" Rotational Period = 243 days ( retrograde) o Solar day on Venus = 117 Earth days o Why retrograde -> collision? Atmosphere o very dense => high altitude clouds of sulfuric acid block surface 90x as massive as the Earth's atmosphere o 96.5% CO2 (by volume) o few % Nitrogen (very little water) surface temperature = 730K (TEarth=300K, TMercury=100-700K) Greenhouse Effect o temperature uniformity - poles, equator, day, night Exploration of Venus More than 20 spacecraft have visited, more than any other planet o o o visits began in the early 1960's first soft landing on surface by Soviet Venera 7 in 1970 Magellan - August 1990 produced spectacularly detailed surface images resolution of about 120 m Venus' atmosphere is different from Earth's? On Earth, CO2 is absorbed in the oceans and rocks. Summary of Atmospheric Components (percentages by volume) CO2 Nitrogen Water Oxygen Earth absorbed in rock free in atmosphere (78%) mostly condensed on surface product of life (21%) Venus free in atmosphere (96.5%) free in atmosphere (3.5%) decomposed long ago, and hydrogen escaped no life to produce it Evolution of Venus' Atmosphere During secondary atmosphere formation temperature of Venus high o no oceans form (Water is broken down and H escapes) and gases are not absorbed o gases in atmosphere trap heat (greenhouse effect) o temperature rises even more o runaway greenhouse effect Venus' Surface A couple of continental sized features o Ishtar Terra (southern high latitudes) o Aphrodite Terra (near the equator), o with Earth-like mountains No oceans o rolling plains (65%) o lowlands (27%) o modest highlands (8%) (continents) No plate tectonic activity Lava flows -> volcanic origin Craters - mostly of volcanic origin The surface of Venus is rather young (less than 1 billion years) due to volcanic activity Volcanism today? Probably (SO levels above the thick cloud cover and suggestive radio emissions) 2 Venus' Magnetic Field and Internal Structure Magnetic field - none detectable o this is consistent with slow rotation period of 243 days Model of internal structure is based on little hard data o Surface resembles surface of young Earth (at an age of about 1 billion years) thin crust, volcanic activity, internal convective processes not yet established not yet developed plate tectonics o Why no development of plates? Cooling slowly due to high surface temperature crust remains too soft for Earth-style plates to develop absence of water may also be important no lubricating mechanism Mars A Near Miss for Life? General Properties of Mars Mars is the 4th Planet from the Sun semi-major axis ("radius") = 1.52 AU closest opposition roughly every 15 years (in August/September) > brightest orbital period = 687 days (1.88 years) Radius = 0.53 Rearth Mass = 0.11 Mearth => Density = 3900 kg/m3 Rotational Period = 24.6 hours Inclination of 24.0° (23.5° for Earth) o tilt causes seasons History of Observations from Earth 1877 - Mars is unusually close to Earth o Italy: Giovanni Schiaparelli Observed network of linear markings (canali) o Percival Lowell, in US Motivated by report of "canals", gives up successful Boston business to build observatory in Flagstaff, Arizona devoted life to studying "canals" and Martian intelligent society Space Probes to Mars Mariner 4 (1965) o First spacecraft to reach Mars Viking 1 and Viking 2 (1976) o landed on Mars and conducted biological experiments to search for evidence of life Pathfinder (& Sojouner, landed July 4, 1997) o landed at mouth of outflow channel o rocks deposited by flood water Mars Global Surveyer o launched November, 1996 o start mapping, March, 1999 Mars Exploration Rover Mission o Spirit landed on January 3, 2004, in a rocky landscape o Opportunity landed halfway around Mars from Spirit found rocks that had been very wet in the past, after landing on January 23, 2004. o The rovers were expected to last 3-6 months, but each continued to explore over a few kilometers and send data back for several years. Spirit stopped communicating in 2010 after traveling over 7 kilometers Opportunity goes on, having traveled over 27 kilometers Phoenix Mission o landed in North polar region in 2008 o dug trenches and discovered white material that is almost surely ice Major results of these missions 1. the surface of Mars contains much more iron that the surface of the Earth less differentiation on Mars 2. so far, no evidence of life, now or in the past o Mars' Atmosphere Mars has a very thin atmosphere o (1/150 of Earth's atmosphere) o 95.3% CO2 (by volume) o surface temperature: noon, summertime 300K night-time - 200K (much colder than on Earth) (Tearth=300K) => dust storms (occasionally months-long) Composition of Mars' atmosphere similar to Venus, yet 10,000 times thinner o -> reverse greenhouse effect Mars' Surface Huge shield volcanoes: o Olympus Mons About 700 kilometers in diameter would cover all of Washington and half of Oregon Rises 25 kilometers above the surrounding plains (82,000 feet) (largest volcano in the Solar System) o Mariner Valley crack in the surface of the planet huge canyon running along the equator for about 4000 km -about 1/5 the circumference Vast dune fields: North-south asymmetry: o Northern Hemisphere: lava plains -> younger surface o Southern Hemisphere: heavily cratered highlands -> older surface THE MAJOR FEATURE: o Tharsis bulge size of North America, near equator rises 10 km above rest of surface Impact cratering: o wide spread cratering, o eroded by the atmosphere o appearance of craters (liquid splash) suggest permafrost (water ice) just below the surface compare this to typical craters on the Moon, such as Copernicus, shown here on the left Running water in the past: o the best evidence that water once existed in great quantities on the surface is the channels runnoff channels: southern highlands 4 billions years ago - thick atmosphere & surface water outflow channels:(another view) near equator from south to north enormous flow rates> 100xAmazon about 3 billion years ago o No water today on the surface a large amount of this water may now be locked in the polar caps and under the surface (permafrost) Polar Caps o north and south o primarily dry ice (CO2) o seasonal variation o temperature remains below 150K Mars' Magnetic Field and Internal Structure Mars' has a weak magnetic field o => about 1/800 of Earth o (but rotation period is similar to Earth 24.6 hours) so -> core is non-magnetic, or has no liquid, or both planet probably never differentiated much o - large abundance of surface iron Moons of Mars Two very small moons: o Phobos (fear) & Deimos (panic) Irregularly shaped and cratered Orbits at about 3 and 7 planetary radii (Earth's Moon orbits at about 60 radii) Both orbit synchronously tidally locked, like the Moon Both orbit prograde direction Large (Stickney) Crater on Phobos Captured asteroids? o low density like typical asteroid Martian Asteroids and the Evidence for Life on Mars About a dozen meteorites from the surface of Mars have been found on Earth o (identified by gases trapped in rocks) 1984 - scientists discovered a rock ( ALH84001) on Antarctic ice field 1992 - detailed study of the rock - found (within a small region of the rock) 1. organic molecules that might be associated with life 2. several minerals characteristic of biological activity 3. tiny tubular and egg-shaped structures resembling ancient single-celled bacteria found on Earth These observations were announced August 7, 1996 This evidence cannot be established as due to life forms o The features could all have been produced by chemical reactions without any involvement of life o Could ALH84001 have been contaminated? (it sat on ice in Antarctica for 13,000 years) o More evidence is need to resolve this NASA plans future visits to Mars to attempt to understand whether life did or did not exist on Mars in the past Jupiter Giant of the Solar System Jupiter is the third brightest object in the night sky (after the Moon and Venus) Differential rotation o period of rotation at equator shorter than at higher latitudes Equatorial bulge due to rapid rotation Prominent visual features o Bands: belts and zones o Great Red Spot o four prominent moons Discovered by Galileo in 1609 It takes over half an hour for light (or radio signals from a spacecraft) to get from Jupiter to the Earth Jupiter as a "failed star" o If Jupiter's mass were 80 times larger, the gravitational collapse would have ignited its hydrogen into thermonuclear fusion, creating a second star in the Solar System o Discovery of Jupiter Jupiter has been known of since ancient time since it is bright in the night sky Space Probes to Jupiter Pioneer 10 - (launched by USA, March 3, 1972) o flew by Jupiter on December 1, 1973 o Carrying a gold, anodized plaque intended to communicate with extraterrestrials Pioneer 11 - (launched by USA, April 6, 1973) o flew by Jupiter on December 1, 1974 o flew by Saturn in 1979 Voyager 1 - (launched by USA, September 5, 1977) o Voyager 1 flew by Jupiter on March 5, 1979 o flew by Saturn on Nov 13, 1980 Voyager 2 - (launched by USA, August 20, 1977) Voyager 2 flew by Jupiter on July 9, 1979 flew by Saturn on Aug 27, 1981 o flew by Uranus on Jan 30, 1986 o flew by Neptune on Aug 15, 1989 Galileo - (launched by USA and Europe, October 18, 1989) o Galileo was designed to study Jupiter's atmosphere, satellites and surrounding magnetosphere for 2 years. o o o o During the journey, Galileo made encounters with asteroids Gaspra on October 29, 1991 Ida and moon Dactyl on August 28, 1993. During voyage, had direct view of the Comet ShoemakerLevy impacts on Jupiter (July, 1994) Arrived at Jupiter, December, 1995 Significantly advanced our knowledge of the Galilean moons Atmosphere of Jupiter Elemental Makeup of Jupiter's Atmosphere o o o o 86.1% molecular hydrogen (by number) 13.8% helium (by number) traces of methane (CH4), ammonia (NH3), and water vapor (H2O) little of the early atmosphere escaped due to the strong gravity (large escape velocity) Clouds: Bands and Spots caused by different chemistry vs. altitude Zones and belts appear as we see different depths of the atmosphere o o Zones (light warm, rising regions) Belts (dark ; cool, falling regions) Zonal Flow Great Red Spot o Large hurricane in the south about 2 times the size of Earth at least 300 years old revolves with inner region of Jupiter rotates counterclockwise o o Other storm related features o o gigantic lightning flashes and Auroral activity White ovals and Brown ovals persist for many years or decades Rings of Jupiter Faint ring discovered by Voyager I Main ring lies above cloud layer and inside orbit of innermost moon Galileo spacecraft has explored the ring, and concluded that the ring system ( main ring + gossamer rings) has been formed by the dust kicked up when interplanetary meteoroids smash into the inner moons Internal Structure and Magnetosphere of Jupiter Jupiter's Internal Structure Emits twice as much energy as it receives from the Sun ---> internal heat built up during Jupiter's formation is slowly leaking out gravitational energy Atmosphere gets denser and denser towards its interior gaseous hydrogen liquid hydrogen liquid metallic hydrogen (generates large magnetic field) rocky core (about 5 times Earth's mass) Jupiter's Magnetosphere Intrinsic strength of magnetic field nearly 20,000 times Earth surface magnetic field 14 times Earth's surface field field oriented opposite to Earth's Very large magnetosphere ----> larger than size of the sun Large sea of trapped, charged particles ----> like Van Allen Belts Plasma torus (moon Io) Moons of Jupiter 63 known moons 16 major moons of greater than 10 km diameter Four sets of four or five moons each Tidally locked 1.) Inner moons (inside Galilean) = 4 small moons 2.) Galilean moons ( 4 moons) discovered by Galileo in 1609 largest, similar in size to Earth's Moon 3., 4.) Outer moons ----> 2 sets of 4 known major moons Each set appears to have been a single body, captured by Jupiter, then broken into 4 major sections each. Orbital motion inner 3 sets are prograde outer set is retrograde Galilean Moons of Jupiter orbits are prograde, circular, and lie in Jupiter's equatorial plane all rotate synchronously (tidal lock) Galileo spacecraft has been on a tour of discovery around the Galilean moons Io: Most geologically active object in Solar System Voyager's observed erupting volcanoes plasma torus produced by Io in Jupiter's magnetosphere volcanoes caused by Jupiter's tidal forces + Europa's influence Europa: surface network of lines : cracks in ice cover? Ocean? Ganymede: largest moon in Solar System (larger than Earth's Moon, Mercury or Pluto) ---> largely ice Callisto: cratering and concentric rings