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Earth the Moon's Surface

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Earth the Moon's Surface Earth The Moon’s surface • The Moon: basic characteristics • Never see the far side: reasons; 59% of surface – Size, Mass, Density, Gravity (near and far side) • Dark spots – Atmosphere, water, magnetic field, surface temperature – Lunar seas – Structure: • Remains of lava flows •Crest •Craters – lithosphere • Mantle – 30 000 with d>1km • Core – Circular – Age of the surface • Light spots – Highlands Mars Satellites of Mars discovered 1877 Phobos: 23 km, 7h 39 min, 9378 km Deimos: 15 km, 1.26 days, 23460 km Mass of Mars Courtesy Calvin J. Hamilton Credit & Copyright: Johannes Schedler 1 Jupiter’s satellites Io Europa Callisto Ganymede • 52+ natural satellites: 20 of them are Discovered in 2003 • Rings discovered in 1979 by Voyager 1 spacecraft Two Sides of Io. Io The orange colored deposits are sulfur snow; the white color is sulfur dioxide. 2 Volcanic Plume on Io An enormous volcanic feature that is Volcanic activity on Io and tidal heating rising about 250 km above Io’s surface. Giant Lava Flow on Io The longest active lava flow yet discovered in the solar system (500 x 200 km). Fig 11-13, p.251 Europa Europa - cracks on the surface Europa is a strange looking moon of Jupiter with a large number of intersecting features. 3 Radius = 2631 km Europa – internal structure Ganymede is the largest moon of Jupiter and is the largest natural satellite in our solar system. Surface – similar to Moon, but icy. Callisto Callisto Jupiter’s outermost large satellite shows a heavily cratered surface of dark ice. 4 What is interesting about Saturn the Jovian Moons? ¾ Io has acting volcanoes due to tidal deformations 31+ moons, 7 large Icy surfaces, different ¾ Europa – covered with water ice. activity in the past. Is there liquid water under the ice? Titan: heavy atmosphere ¾ Ganymede – the largest moon in the Solar system, of mostly nitrogen, bigger than Mercury and Pluto. Surface similar argon and methane. to the Moon, but icy. Weak magnetic field. Surface T ~ -180oC ¾ Calisto –heavily cratered A near-infrared view of Uranus and Uranus moons Miranda (top) and Ariel • 5 moderate size satellites which masses and densities are known – Low densities – mixture of rock and ice – Their surfaces are dark – Many impact craters – Some signs of geological activity in the past – Signs of tidal heating in the past: Miranda • 16+ small moons 5 The surface of Miranda is covered with craters, canyons, valleys, and cliffs. The surface of Titania is The surface of The surface of Umbriel is covered in craters and Ariel is covered The surface of heavily cratered and is interconnected valleys. with craters and Uranus' darkest satellite. Oberon is heavily long rift valleys. cratered and icy. 6 Neptune Triton – Neptune’s largest satellite • Neptune’s satellites - small ice bodies • Triton – Neptune’s largest satellite – Retrograde orbit – High orbital inclination with respect to Neptune’s equator – The only large satellite with retrograde orbit. Probably captured ? – Surface – icy (water ice on the surface), reflective, impact craters and cracks – Surface T ~ -236oC – Thin nitrogen atmosphere – Nitrogen geysers observed. – Internal heat in the past but not now – The radius of Triton’s orbit is decreasing – will be destroyed by the tidal force (in ~ 100 mill yrs) Pluto and Charon are tough to see even with the best telescopes Triton • There are very few craters visible; the surface is relatively young. • Almost the entire southern hemisphere is covered with an "ice cap" of frozen nitrogen and methane. • There are extensive ridges and valleys in complex patterns all over Triton's surface. These are probably the result of freezing/thawing cycles. • The most interesting (and totally unexpected) features are the ice volcanoes. 7 The largest satellites in the Solar System Orbit on its side. Charon is in a prograde orbit – probably born with Pluto The Kuiper Trans-Neptunian Objects (TNO) Belt Any object in the solar system that orbits the Sun at a greater distance on average than Neptune The Kuiper belt, Scattered disk, and Oort cloud are names for three divisions of this volume of space. Courtesy of Courtesy of Windows to the Windows to the Universe, Universe, http://www.windows.ucar.edu http://www.wind ows.ucar.edu 8 Comparing the small distant ‘planets’ Kuiper belt objects: Planet to the Earth candidates in the Solar System About 800 objects (diameter > 50 km) are currently known in the Kuiper belt beyond Neptune. Cold icy worlds at 40-50 A.U. from the Sun. The largest: Pluto, Charon, 2003 UB313 Gerard Kuiper (1951) The scattered disk objects and the Oort Cloud Courtesy of Windows 50,000 to 100,000 AU from the Sun to the Universe, http://www.windows.uc ar.edu 9 COMETS AND THE OORT CLOUD COMETS AND THE OORT CLOUD • Comets are "dirty snowballs," few km across, largely ice, small rocky cores • Orbit around the Sun on elongated elliptical orbits. • As comet approaches Sun, ice evaporates, dust escapes, comet becomes much brighter • Pressure of Sun's light and "solar wind" (particles streaming from Sun) stretch evaporating gas and dust into long, reflective tail. • Long orbital periods (millions of years), semi-major axis of ~ 1000-50,000 AU. • Come from distant, spherical reservoir surrounding Sun, called the Oort Cloud. • Deflected into inner solar system by gravity of passing stars (nearest star today is 200,000 AU from Sun). • Asteroids and comets are debris left over from early solar system. Oort cloud is material kicked out of the inner solar system by gravitational interactions with Jupiter. Comet Halley Parts of a Comet. This composite of three images This schematic (one in red, one in green, one in illustration shows blue) shows Comet Halley as the main parts of a seen with a large telescope in comet. Australia in 1985. Nucleus Coma – spherical cloud of gas and dust Invisible cloud of hydrogen Plasma Tail Dust Tail Edmund Halley (1656–1742). Fig 12-13, p.277 10 Comet Hale–Bopp was one of the most attractive and easiest to see comets of the 20th century. It is shown here as it appeared in the sky Comet Tail Points Away from the on March 8, 1997. You can see the Sun. comet’s long blue ion tail and the shorter white dust tail. The orientation of a typical comet tail changes as the comet passes perihelion. Comet Tails. The smoother tail of dust curving to the right as individual dust particles spread out along the comet’s orbit, and the straight ion tail pushed outward from the Sun by its wind of charged particles. A particle that is believed to be a tiny fragment of cometary dust, collected in the upper atmosphere of the Earth. Fig 12-19, p.280 11 Close-ups of Comets Halley and Borrelly This historic photograph of the black, irregularly shaped nucleus of Comet Halley was Close-ups of Comets Halley and Borrelly obtained by the Giotto spacecraft from a distance of about 1000 km. The bright areas Even more detail is visible in this photo of Comet Borrelly taken at a range of 3000 are jets of material escaping from the surface. The length of the nucleus is 10 km, and km. The nucleus is 8 km long and very dark, with an average reflectivity less than 2 details as small as 1 km can be made out. percent. Head of Comet Halley Here we see the cloud of gas and dust that make up the head or coma of Comet Halley on January 20, 1986. On this scale, the nucleus (hidden inside the cloud) would be a dot too small to see. Fig 12-17, p.279 12.
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