ALBERT

Description: Voyager 2 images of Neptune reveal a windy planet characterized by bright clouds of methane ice suspended in an exceptionally clear atmosphere above a lower deck of hydrogen sulfide or ammonia ices. Neptune's atmosphere is dominated by a large anticyclonic storm system that has been named the Great Dark Spot (GDS). About the same size as Earth in extent, the GDS bears both many similarities and some differences to the Great Red Spot of Jupiter. Neptune's zonal wind profile is remarkably similar to that of Uranus. Neptune has three major rings at radii of 42,000, 53,000, and 63,000 kilometers. The outer ring contains three higher density arc-like segments that were apparently responsible for most of the ground-based occultation events observed during the current decade. Like the rings of Uranus, the Neptune rings are composed of very dark material; unlike that of Uranus, the Neptune system is very dusty. Six new regular satellites were found, with dark surfaces and radii ranging from 200 to 25 kilometers. All lie inside the orbit of Triton and the inner four are located within the ring system. Triton is seen to be a differentiated body, with a radius of 1350 kilometers and a density of 2.1 grams per cubic centimeter; it exhibits clear evidence of early episodes of surface melting. A now rigid crust of what is probably water ice is overlain with a brilliant coating of nitrogen frost, slightly darkened and reddened with organic polymer material. Streaks of organic polymer suggest seasonal winds strong enough to move particles of micrometer size or larger, once they become airborne. At least two active plumes were seen, carrying dark material 8 kilometers above the surface before being transported downstream by high level winds. The plumes may be driven by solar heating and the subsequent violent vaporization of subsurface nitrogen.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, B A -- Soderblom, L A -- Banfield, D -- Barnet, C -- Basilevsky, A T -- Beebe, R F -- Bollinger, K -- Boyce, J M -- Brahic, A -- Briggs, G A -- Brown, R H -- Chyba, C -- Collins, S A -- Colvin, T -- Cook, A F 2nd -- Crisp, D -- Croft, S K -- Cruikshank, D -- Cuzzi, J N -- Danielson, G E -- Davies, M E -- De Jong, E -- Dones, L -- Godfrey, D -- Goguen, J -- Grenier, I -- Haemmerle, V R -- Hammel, H -- Hansen, C J -- Helfenstein, C P -- Howell, C -- Hunt, G E -- Ingersoll, A P -- Johnson, T V -- Kargel, J -- Kirk, R -- Kuehn, D I -- Limaye, S -- Masursky, H -- McEwen, A -- Morrison, D -- Owen, T -- Owen, W -- Pollack, J B -- Porco, C C -- Rages, K -- Rogers, P -- Rudy, D -- Sagan, C -- Schwartz, J -- Shoemaker, E M -- Showalter, M -- Sicardy, B -- Simonelli, D -- Spencer, J -- Sromovsky, L A -- Stoker, C -- Strom, R G -- Suomi, V E -- Synott, S P -- Terrile, R J -- Thomas, P -- Thompson, W R -- Verbiscer, A -- Veverka, J -- New York, N.Y. -- Science. 1989 Dec 15;246(4936):1422-49.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17755997" target="_blank"〉PubMed〈/a〉

Description: Voyager 2 images of the southern hemisphere of Uranus indicate that submicrometersize haze particles and particles of a methane condensation cloud produce faint patterns in the atmosphere. The alignment of the cloud bands is similar to that of bands on Jupiter and Saturn, but the zonal winds are nearly opposite. At mid-latitudes (-70 degrees to -27 degrees ), where winds were measured, the atmosphere rotates faster than the magnetic field; however, the rotation rate of the atmosphere decreases toward the equator, so that the two probably corotate at about -20 degrees . Voyager images confirm the extremely low albedo of the ring particles. High phase angle images reveal on the order of 10(2) new ringlike features of very low optical depth and relatively high dust abundance interspersed within the main rings, as well as a broad, diffuse, low optical depth ring just inside the main rings system. Nine of the newly discovered small satellites (40 to 165 kilometers in diameter) orbit between the rings and Miranda; the tenth is within the ring system. Two of these small objects may gravitationally confine the e ring. Oberon and Umbriel have heavily cratered surfaces resembling the ancient cratered highlands of Earth's moon, although Umbriel is almost completely covered with uniform dark material, which perhaps indicates some ongoing process. Titania and Ariel show crater populations different from those on Oberon and Umbriel; these were probably generated by collisions with debris confined to their orbits. Titania and Ariel also show many extensional fault systems; Ariel shows strong evidence for the presence of extrusive material. About halfof Miranda's surface is relatively bland, old, cratered terrain. The remainder comprises three large regions of younger terrain, each rectangular to ovoid in plan, that display complex sets of parallel and intersecting scarps and ridges as well as numerous outcrops of bright and dark materials, perhaps suggesting some exotic composition.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Smith, B A -- Soderblom, L A -- Beebe, R -- Bliss, D -- Boyce, J M -- Brahic, A -- Briggs, G A -- Brown, R H -- Collins, S A -- Cook, A F 2nd -- Croft, S K -- Cuzzi, J N -- Danielson, G E -- Davies, M E -- Dowling, T E -- Godfrey, D -- Hansen, C J -- Harris, C -- Hunt, G E -- Ingersoll, A P -- Johnson, T V -- Krauss, R J -- Masursky, H -- Morrison, D -- Owen, T -- Plescia, J B -- Pollack, J B -- Porco, C C -- Rages, K -- Sagan, C -- Shoemaker, E M -- Sromovsky, L A -- Stoker, C -- Strom, R G -- Suomi, V E -- Synnott, S P -- Terrile, R J -- Thomas, P -- Thompson, W R -- Veverka, J -- New York, N.Y. -- Science. 1986 Jul 4;233(4759):43-64.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17812889" target="_blank"〉PubMed〈/a〉

Description: Images were acquired of a circumstellar disk of orbiting material around the nearby star beta Pictoris. This material is believed to be associated with the formation of planets and provides a first look at a planetary system much younger than our own. Preliminary work was also done to acquire multicolor photometric data and polarimetry on the beta Pictoris disk as well. A coronagraphic search for other proto-planetary systems is also underway. Coronagraphic imaging provided the first clear images and a determination of the geometric albedo of the rings of Uranus. A search for material around the asteroid Amphitrite showed that the region around the asteroid was free of particles larger than 500 meters in radius or diffuse material with an optical depth larger than .000001. NASA IRTF infrared images of Jupiter and Saturn are providing information on the relative heights and cloud top temperatures of atmospheric features.

Description: The purpose of this investigation is to obtain and analyze high spatial resolution charge coupled device (CCD) coronagraphic images of extra-solar planetary material and solar system objects. These data will provide information on the distribution of planetary and proto-planetary material around nearby stars leading to a better understanding of the origin and evolution of the solar system. Imaging within our solar system will provide information on the current cloud configurations on the outer planets, search for new objects around the outer planets, and provide direct support for Voyager, Galileo, and CRAF by imaging material around asteroids and clouds on Neptune. Over the last year this program acquired multispectral and polarization images of the disk of material around the nearby star Beta Pictoris. This material is believed to be associated with the formation of planets and provides a first look at a planetary system much younger than our own. Preliminary color and polarization data suggest that the material is very low albedo and similar to dark outer solar system carbon rich material. A coronagraphic search for other systems is underway and has already examined over 100 nearby stars. Coronagraphic imaging provided the first clear look at the rings of Uranus and albedo limits for the ring arcs around Neptune.

Description: This paper discusses recent work in the development of instrumentation used for the direct detection of planetary systems from ground-based and space-based observatories. Direct methods such as CCD coronagraphic imaging of nearby stars must overcome the large contrast differences between parent star and the circumstellar material. However, these methods have the advantage over indirect methods in that more advanced space-based direct detection instrumentation can lead to a significantly greater science return.

Description: Several sequences of the dark (Jupiter-illuminated) side of Io obtained during the Voyager 2 encounter present opporunity for understanding several problems relating to the surface composition of Io. The existence or absence of SO2 condensates on the night side is a sensitive indicator of an SO2 atmosphere. Preliminary analysis of the night side Io images suggests localized brightenings of approximately 25% may exist. Examination of the night side images represents an even more sensitive indicator for pure sulfur. Between 60 and 130 degrees (the minimum nighttime and maximum daytime temperatures, respectively), the relative spectral reflectance for yellow sulfur observed in the Voyager green and clear filters decreases by 25%. This decrease should be detectable on the nightside images. A search of the Voyager 2 Jupiter-illuminated images yielded a single pair of green and clear images. In these images one hemisphere of Io is Sun-illuminated and the other is Jupiter illuminated. Geologically similar regions of Io are being selected to obtain average color ratios of specific geologic units for both day and night sides.

Description: The direct detection of extrasolar planets by imaging will require reductions in scattered and diffracted light by factors in excess of 1000 within one arcsecond of a bright source. While diffraction can be reduced by a number of approaches, small angle scatter can only be reduced by controlling midspatial frequency figure errors. The surface requirements are reviewed and their meaning when compared to the data base of existing mirrors is considered. Experiments are discribed that were successful in reducing midspatial frequency figure so that the scatter level was 500 times less than diffraction for a 25-cm spherical mirror.