Surface and Airborne Evidence for Plumes and Winds on Triton

Dunes on Pluto

The surface of Pluto is more geologically diverse and dynamic than had been expected, but the role of its tenuous atmosphere in shaping the landscape remains unclear. We describe observations from the New Horizons spacecraft of regularly spaced, linear ridges whose morphology, distribution, and orientation are consistent with being transverse dunes. These are located close to mountainous regions and are orthogonal to nearby wind streaks. We demonstrate that the wavelength of the dunes (~0.4 to 1 kilometer) is best explained by the deposition of sand-sized (~200 to ~300 micrometer) particles of methane ice in moderate winds (<10 meters per second). The undisturbed morphology of the dunes, and relationships with the underlying convective glacial ice, imply that the dunes have formed in the very recent geological past.

[Understanding of cerebrospinal fluid hydrodynamics in idiopathic hydrocephalus (A) Visualization of CSF bulk flow with MRI time-spatial labeling pulse method (time-SLIP)]

Cerebrospinal fluids (CSF) hydrodynamics in normal and hydrocephalic brain was observed noninvasively using a time-spatial labeling inversion pulse (SLIP) technique. A time-SLIP technique applied label to CSF in the region of interest so that CSF became internal CSF tracer. CSF hydrodynamics even in normal brain appeared to be much different from it was imagine from conventional CSF physiology text books. Various amplitudes of pulsatile CSF flow were observed in the different regions of the brain. CSF hydrodynamics altered when hydrocephalus was developed. A time-SLIP CSF flow imaging is helpful to understand CSF hydrodynamics in the normal physiological and hydrocephalic brain. It may be useful to distinguish the hydrocephalus brain from the senile atrophic brain.

Subsurface Energy Storage and Transport for Solar-Powered Geysers on Triton

The location of active geyser-like eruptions and related features close to the current subsolar latitude on Triton suggests a solar energy source for these phenomena. Solidstate greenhouse calculations have shown that sunlight can generate substantially elevated subsurface temperatures. A variety of models for the storage of solar energy in a sub-greenhouse layer and for the supply of gas and energy to a geyser are examined. "Leaky greenhouse" models with only vertical gas transport are inconsistent with the observed upper limit on geyser radius of approximately 1.5 kilometers. However, lateral transport of energy by gas flow in a porous N(2) layer with a block size on the order of a meter can supply the required amount of gas to a source region approximately 1 kilometer in radius. The decline of gas output to steady state may occur over a period comparable with the inferred active geyser lifetime of five Earth years. The required subsurface permeability may be maintained by thermal fracturing of the residual N2 polar cap. A lower limit on geyser source radius of approximately 50 to 100 meters predicted by a theory of negatively buoyant jets is not readily attained.

Triton's Geyser-Like Plumes: Discovery and Basic Characterization

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.