Neptune

1. Neptune Roman God of the Oceans or Seas Trident Symbol The truly “Blue” Planet

2. General Information • Eighth planet from the Sun • Discovered in 1846 (has yet to complete a full orbit since that time) • Thought to be similar in make-up to Uranus • Smallest of the outer “gas giants” • 6% the size of Jupiter (volume > 60 Earth’s) • Probable relatively undifferentiated core of rocky and “icy” materials • Perhaps not segregated into discrete shells like on most other planets • ~45% of mass is rocky portion • <50% ices • Water, methane (CH4) and ammonia (NH3)

3. General Information • Distinctive magnetic field • Small but significant magnetic field • 25% Earth’s strength • Magnetic poles are tilted ~50 degrees relative to rotational axis • Center of field is displaced from center of planet ~10,000km toward south pole • Resides in watery shell or mantle • Caught in a magnetic polar reversal? • Constantly changing w/respect to planets orbit • Emits a significant amount of heat • More homogenous rather than layered internal structure • May be factor allowing Neptune to lose heat through convection unlike layered Uranus • Solar insolation falls on equator rather than on poles as Uranus

4. Planetary Statistics • Mean distance from Sun: 4,498,252,900km • 30.07 A.U. • Orbital Period = 60,190 days (164.8 Earth yrs) • Rotational Period = 16 hours • Refined by Voyager measurements • Axis Tilt = 28.8 degrees (23.5) • Diameter = 49,528km (7926km) • Mass = 1.02 x 1026 (5.97 x 1024) • Density = 1.64g/cm3 (5.515gm/cm3)

5. Planetary Statistics (cont’d) • Equatorial surface gravity = 11.0m/sec2 (9.78m/sec2) • Visual albedo = 0.41 (.37) • Moons = 8 • 6 of which were found by Voyager 2 • Atmospheric composition • Hydrogen 85% • Helium 13% • Methane 2% (at depth) • Acetylene (other hydrocarbons) • Formed in upper atmosphere by interactions with solar energy • Mean surface temperature = 48k (F) • Rings • Narrow • Contain concentrations of particles called ring arcs

6. Internal Composition • Our knowledge of the internal structure of Neptune is inferred from the planet's radius, mass, period of rotation, the shape of its gravitational field and the behavior of hydrogen, helium, and water at high pressure • Outer envelope composed of molecular hydrogen, helium and methane roughly the mass of one to two Earths • Below this region is a mantle rich in water, methane, ammonia, and other elements • Under high temperatures and pressures deep within the planet • Equivalent to 10 to 15 earth masses • Core is composed of rock and ice, and is likely no more than one Earth mass

7. Neptune’s Clouds & Great Dark Spot • The bright cirrus-like clouds of Neptune change rapidly, often forming and dissipating over periods of several hours • In this sequence spanning two rotations of Neptune (about 36 hours) Voyager 2 observed cloud evolution in the region around the Great Dark Spot (GDS) at an effective resolution of about 100 kms per pixel • Earth and the GDS are of similar size and in Neptune's frigid atmosphere, where temperatures are as low as 55 degrees Kelvin (-360 F), the cirrus clouds are composed of frozen methane rather than Earth's crystals of water ice

8. Neptune’s Clouds (cont’d) • This image shows bands of sunlit cirrus-like clouds in Neptune's northern hemisphere • The white streaky clouds are from 48 to 160 kms (30 to 100 mi) wide and extend for thousands of miles • Neptune – fastest winds in SS • >1,000mph

9. Great Dark Spots • GDS is at same latitude as Jupiter’s GRS (20S) • Relatively permanent • Caused by wind shear of opposing latitudinal jet-stream bands • Hurricane-like storms

10. Neptune’s Ring System • Two 591-second exposures of the rings taken by Voyager 2 • Two main rings are clearly visible and appear complete • Also visible is the inner faint ring at about 42,000 kms from the center of Neptune, and the faint band which extends smoothly from the 53,000 km ring to roughly halfway between the two bright rings

11. Distorted Rings • Portion of one of rings appears to be twisted • Believed to look this way because the original material in the rings was in clumps • The motion of the spacecraft added to the twisted appearance by causing a slight smearing in the image

12. Neptune’s Ring System • Composed of three rings and several diffuse sheets • Differing concentrations of small, dark particles • Ring arcs • Collections of particles at Lagrangrian points • 60 degree separation in orbit of moon • Preceding and following • Four moons orbit within the ring system • All are dark surfaced • May have material or composition in common • Lie within the Roche Limit • Tidal disruption • Halted accretion

13. Neptune’s Satellites • Only 3 moons > 300km in diameter • Triton and Nereid discovered by telescopic observations from Earth • Two strangest satellite orbits in the SS • Triton orbits in retrograde motion w/21 degree orbital tilt • Nereid has most inclined orbital plane and greatest eccentricity (9 million miles from Neptune) • 359 Earth days for one orbit • Voyager discovered 6 moons within and near the ring system • All are dark • None appear to be shepherds • Outermost is largest Proteus • Not enough mass to be spherical

14. Triton • Neptune’s inner most and largest moon • Retrograde circular orbit around Neptune • May have originally been more elliptical • Significant amount of tidal flexing • Warm interior • 21 degree inclined orbital plane • 600 year cycle of seasons • Polar axis can be tilted 40 degrees toward the Sun • Currently northern winter • Polar to atmosphere to polar transfer of nitrogen caused by solar energy fluctuations during long seasonal periods • Methane and nitrogen ices at surface • Coldest surface we’ve visited (37K) • Sublimation produces very thin atmosphere • One of three nitrogen rich atmospheres in SS

15. Triton’s Geology • Three distinct terrains (from oldest to youngest) • Highly fractured plains • Cantaloupe terrain • Rifting • Grabens • Filled with extrusions of a viscous, nearly solid material • Not heavily cratered • < 3 byo • Flooded volcanic plains • Circular to arcurate flooded calderas • More fluid than material above • May contain ammonia to lower melting point and decrease viscosity • Polar ice caps • Bright cap extends almost to equator in southern hemisphere • Temporary sink for atmospheric volatiles • Albedo approaching 90% • Active eruption plumes near northern edge of cap (appear dark) • Geysers very young atop cap material

16. Triton • One of only three objects in the SS known to have a nitrogen-dominated atmosphere • Coldest surface known anywhere in the SS (38 K, about -391 degrees F) • So cold that most of N is condensed as frost • Only satellite in the SS known to have a surface made mainly of N ice • Pinkish deposits constitute a vast south polar cap believed to contain methane ice • Dark streaks overlying pink ices believed to be an icy and carbonaceous dust • Deposited from huge geyser-like plumes, some of which were found to be active during the Voyager 2 flyby • Bluish-green band visible extends around Triton near equator • May consist of relatively fresh nitrogen frost deposits • Greenish areas includes cataloupe terrain • Origin unknown • And a set of 'cryovolcanic' landscapes apparently produced by icy-cold liquids (now frozen) erupted from interior

17. Triton Surface • Computer-generated perspective rendering of one of the caldera-like depressions on Triton • The topography was vertically exaggerated 20 times in producing this perspective view • Actual relief in the region has a maximum range of about 1 km in the 13 km diameter impact crater visible in the center of the image • Caldera floor, ~200 km in diameter, is extremely flat and probably was formed by the volcanic eruption of ice lavas of very low viscosity • Bench visible in the foreground may be a remnant of earlier flooding to a level about 200 m higher than the present calderas floor

18. Triton’s South Polar Cap • High resolution image of Triton by Voyager 2 and shows the moon's south polar cap • One of the unusual aspect of this image is the dark streaks in the images • Perhaps geyser-like eruptions of nitrogen • The geyser eruptions could have carried darker materials from the crust • The light regions probably consist of layers of frozen nitrogen

19. Structure and Craters • Voyager 2 acquired this image of Triton during the night of Aug. 24-25, 1989 • Three irregular dark areas, surrounded by brighter material, dominate the image • Low-lying material with intermediate albedo occupies the central area, and fresh craters occur along the right margin • Sub-parallel alignment of linear patches of dark material shown in the lower and left part of the image suggests that the patches are structurally controlled

20. Voyager 2 Farewell This Voyager 2 image shows a beautiful dual-crescent view of Neptune and Triton. The image, acquired on August 31, 1989, is a parting tribute of the Voyager mission.

21. Pluto • Diameter: 1,494mi (2,390km) or 0.2 Earth diameters • Planetary Mass: 0.0025 Earth masses • Gravity about 0.08 of Earths • If you weighed 150lbs on Earth you would only weigh 10lbs on Pluto • Average Distance from Sun: 39.53 AU • Length of Day: about 6.4 Earth Days • Length of Year: 248.53 Earth Years • Number of natural satellites: 1 - Charon • Planetary ring system: No • Average temp: -223 C (-388F) • Atmospheric composition: Very thin but mostly N and methane

22. Pluto and Charon • Discovered by Clyde Tombaugh in 1930 at Lowell Observatory in Flagstaff, Arizona • When closest to the Sun the frozen methane, nitrogen and CO2 surface may thaw creating a very thin, temporary atmosphere • Charon is about half the size of Pluto, shares the same orbit and thus are essentially a double planet system • Two new moons are in same plane • No spacecraft has ever visited Pluto

23. Pluto • Was smallest planet – largest moon in proportion to its size • Double planet/dwarf system • Diameter is only half the width of the continental U.S. • Denser than satellites of Saturn and Uranus but very similar to Triton • Suggest large silicate component • Temperatures at this distance from the Sun during the formation of the SS may have precluded planetary differentiation • Pluto and Charon may not be layered objects • Still we can see very dark, medium and very bright areas • Dark = silicate rocks • Medium = methane ice • Bright = water ice

24. Pluto • Surface could be more ancient than other objects we’ve visited and so reflects early SS formation • Nearest approach to Sun causes sublimation of N and Methane ices and the creation of a thin atmosphere (it is nearing the end of this phase), when farther out in orbit atmosphere condenses and falls to the surface

25. Pluto • Mike Brown – Caltech the man who “killed” the planet Pluto • Brown finds object larger then Pluto further out in the Kuiper Belt • Has a moon • Pluto-like in composition • Ares goddess of discord • Creates debate about the definition of the term “planet” • Spherical object that orbits Sun and clears out its orbital neighborhood or orbital path • Orbit is same as other planets • Pluto loses out • New Horizons launched 1st space craft to object • If it doesn’t reach the planet in time the atmosphere will condense and the chance to study it will not reoccur for another ~200 years • >45,000mi/hour, fastest spacecraft ever launched • 13 months to Jupiter another 8 yrs to Pluto (2016)

26. New Horizons • 1161 days since launch • 2301 days until encounter

27. The New Horizons team selected instruments that not only would directly measure NASA's items of interest, but also provide backup to other instruments on the spacecraft should one fail during the mission. The science payload includes seven instruments:Ralph: Visible and infrared imager/spectrometer; provides color, composition and thermal maps. Alice: Ultraviolet imaging spectrometer; analyzes composition and structure of Pluto's atmosphere and looks for atmospheres around Charon and Kuiper Belt Objects (KBOs). REX: (Radio Science EXperiment) Measures atmospheric composition and temperature; passive radiometer. LORRI: (Long Range Reconnaissance Imager) telescopic camera; obtains encounter data at long distances, maps Pluto's farside and provides high resolution geologic data. SWAP: (Solar Wind Around Pluto) Solar wind and plasma spectrometer; measures atmospheric "escape rate" and observes Pluto's interaction with solar wind. PEPSSI: (Pluto Energetic Particle Spectrometer Science Investigation) Energetic particle spectrometer; measures the composition and density of plasma (ions) escaping from Pluto's atmosphere. SDC: (Student Dust Counter) Built and operated by students; measures the space dust peppering New Horizons during its voyage across the solar system.