ALBERT

Description: Increasing the helicity injector drive frequency up to 68.5 kHz on the Helicity Injected Torus-Steady Inductive (HIT-SI) experiment has produced spheromaks with current amplifications of 3.8, ideal n  = 1 kink stability, improved toroidal symmetry and pressure confinement. Current centroid calculations from surface magnetic probes show an outward shift in the magnetic field at frequencies above 50 kHz. Grad-Shafranov equilibria indicate pressure confinement at higher injector operating frequencies. The minimum characteristic frequency needed to achieve this confining effect on HIT-SI plasmas is found to be approximately 30 kHz by analysis of the density fluctuations.

Description: The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed an occultation of the Sun by the water vapor plume at the south polar region of Saturn's moon Enceladus. The Extreme Ultraviolet (EUV) spectrum is dominated by the spectral signature of H2O gas, with a nominal line-of-sight column density of 0.90 ± 0.23 × 1016 cm−2 (upper limit of 1.0 × 1016 cm−2). The upper limit for N2 is 5 × 1013 cm−2, or

Description: Sublimation at the ice-substrate interface with pressure build-up is an accepted mechanism for the production of fan deposits on the southern polar CO2 ice cap on Mars. Fluid dynamics modeling has been used to investigate gas outflow through vents in a CO2 slab ice. Small (5–25 m in length) fan deposits seen on the annual southern CO2 ice cap can be produced by a steady-state in which open vents continuously outgas in response to sub-surface sublimation generated by diurnal energy input through translucent impermeable (to gas) ice slabs. This would produce diurnally-controlled deposits which would change orientation with time in response to winds thereby explaining observations made by HiRISE on MRO. Gas flow below the ice can reach up to 25 m/s close to the vent. Dust flow in the sub-ice cavity has also been computed but velocities are much lower with the main acceleration occurring

Description: Author(s): B. S. Victor, T. R. Jarboe, A. C. Hossack, D. A. Ennis, B. A. Nelson, R. J. Smith, C. Akcay, C. J. Hansen, G. J. Marklin, N. K. Hicks, and J. S. Wrobel [Phys. Rev. Lett. 107, 165005] Published Wed Oct 12, 2011

Description: We use data from the High Resolution Imaging Science Experiment (HiRISE) camera and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) imaging spectrometer onboard the Mars Reconnaissance Orbiter to follow the evolution of the appearance and composition of 12 regions of the south polar layered deposits from spring to summer time. We distinguish three steps in the evolution of the volatile layer: a decrease of both CO2 band strength and albedo until Ls = 190°–210°, a significant increase in both until Ls = 240°–260° and finally a rapid decrease until the complete defrosting of the ground. In contrast, the water ice band displays a more monotonic decrease. Analysis of HiRISE color images acquired simultaneously with CRISM data allows a plausible interpretation of this evolution. In early springtime (Ls 〈 200°), intense jet activity results in deposition of fans of large mineral grains and a wide spatial distribution of fine grains. The small-scale topography controls the presence and location of the jets by allowing more solar energy to be collected on slopes. Grains from the dust fans warm and sink through the CO2 layer, resulting in a bluish color at the locations of the fans around Ls = 190°–210°. As the atmosphere warms up, the surface of the ice layer sublimes and releases dust and water, resulting in its brightening. The last phase of the process consists in a progressive defrosting resulting in a patchwork of frozen and unfrozen areas.

Description: Images of Neptune obtained by the narrow-angle camera of the Voyager 2 spacecraft reveal large-scale cloud features that persist for several months or longer. The features' periods of rotation about the planetary axis range from 15.8 to 18.4 hours. The atmosphere equatorward of -53 degrees rotates with periods longer than the 16.05-hour period deduced from Voyager's planetary radio astronomy experiment (presumably the planet's internal rotation period). The wind speeds computed with respect to this radio period range from 20 meters per second eastward to 325 meters per second westward. Thus, the cloud-top wind speeds are roughly the same for all the planets ranging from Venus to Neptune, even though the solar energy inputs to the atmospheres vary by a factor of 1000.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hammel, H B -- Beebe, R F -- De Jong, E M -- Hansen, C J -- Howell, C D -- Ingersoll, A P -- Johnson, T V -- Limaye, S S -- Magalhaes, J A -- Pollack, J B -- Sromovsky, L A -- Suomi, V E -- Swift, C E -- New York, N.Y. -- Science. 1989 Sep 22;245(4924):1367-9.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17798743" target="_blank"〉PubMed〈/a〉

Description: A plume of water vapour escapes from fissures crossing the south polar region of the Saturnian moon Enceladus. Tidal deformation of a thin surface crust above an internal ocean could result in tensile and compressive stresses that would affect the width of the fissures; therefore, the quantity of water vapour released at different locations in Enceladus' eccentric orbit is a crucial measurement of tidal control of venting. Here we report observations of an occultation of a star by the plume on 24 October 2007 that revealed four high-density gas jets superimposed on the background plume. The gas jet positions coincide with those of dust jets reported elsewhere inside the plume. The maximum water column density in the plume is about twice the density reported earlier. The density ratio does not agree with predictions-we should have seen less water than was observed in 2005. The ratio of the jets' bulk vertical velocities to their thermal velocities is 1.5 +/- 0.2, which supports the hypothesis that the source of the plume is liquid water, with gas accelerated to supersonic velocity in nozzle-like channels.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hansen, C J -- Esposito, L W -- Stewart, A I F -- Meinke, B -- Wallis, B -- Colwell, J E -- Hendrix, A R -- Larsen, K -- Pryor, W -- Tian, F -- England -- Nature. 2008 Nov 27;456(7221):477-9. doi: 10.1038/nature07542.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Jet Propulsion Laboratory/California Institute of Technology, Pasadena, California 91109, USA. candice.j.hansen@jpl.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19037310" target="_blank"〉PubMed〈/a〉

Description: Aeolian features on Triton that were imaged during the Voyager Mission have been grouped. The term "aeolian feature" is broadly defined as features produced by or blown by the wind, including surface and airborne materials. Observations of the latitudinal distributions of the features probably associated with current activity (known plumes, crescent streaks, fixed terminator clouds, and limb haze with overshoot) all occur from latitude -37 degrees to latitude -62 degrees . Likely indicators of previous activity (dark surface streaks) occur from latitude -5 degrees to -70 degrees , but are most abundant from -15 degrees to -45 degrees , generally north of currently active features. Those indicators which give information on wind direction and speed have been measured. Wind direction is a function of altitude. The predominant direction of the surface wind streaks is found to be between 40 degrees and 80 degrees measured clockwise from north. The average orientation of streaks in the northeast quadrant is 59 degrees . Winds at 1- to 3- kilometer altitude are eastward, while those at &8 kilometers blow west.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hansen, C J -- McEwen, A S -- Ingersoll, A P -- Terrile, R J -- New York, N.Y. -- Science. 1990 Oct 19;250(4979):421-4.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17793018" target="_blank"〉PubMed〈/a〉

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: At least four active geyser-like eruptions were discovered in Voyager 2 images of Triton, Neptune's large satellite. The two best documented eruptions occur as columns of dark material rising to an altitude of about 8 kilometers where dark clouds of material are left suspended to drift downwind over 100 kilometers. The radii of the rising columns appear to be in the range of several tens of meters to a kilometer. One model for the mechanism to drive the plumes involves heating of nitrogen ice in a subsurface greenhouse environment; nitrogen gas pressurized by the solar heating explosively vents to the surface carrying clouds of ice and dark partides into the atmosphere. A temperature increase of less than 4 kelvins above the ambient surface value of 38 +/- 3 kelvins is more than adequate to drive the plumes to an 8-kilometer altitude. The mass flux in the trailing clouds is estimated to consist of up to 10 kilograms of fine dark particles per second or twice as much nitrogen ice and perhaps several hundred or more kilograms of nitrogen gas per second. Each eruption may last a year or more, during which on the order of a tenth of a cubic kilometer of ice is sublimed.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Soderblom, L A -- Kieffer, S W -- Becker, T L -- Brown, R H -- Cook, A F 2nd -- Hansen, C J -- Johnson, T V -- Kirk, R L -- Shoemaker, E M -- New York, N.Y. -- Science. 1990 Oct 19;250(4979):410-5.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17793016" target="_blank"〉PubMed〈/a〉