Engineering topics

Turtle, E.

Publications and source records attributed to Turtle, E..

8 records

NASA NTRS2013

Crater Topography on Titan: Implications for Landscape Evolution

We present a comprehensive review of available crater topography measurements for Saturn's moon Titan. In general, the depths of Titan's craters are within the range of depths observed for similarly sized fresh craters on Ganymede, but several hundreds of meters shallower than Ganymede's average depth vs. diameter trend. Depth-to-diameter ratios are between 0.0012 +/- 0.0003 (for the largest crater studied, Menrva, D approximately 425 km) and 0.017 +/- 0.004 (for the smallest crater studied, Ksa, D approximately 39 km). When we evaluate the Anderson-Darling goodness-of-fit parameter, we find that there is less than a 10% probability that Titan's craters have a current depth distribution that is consistent with the depth distribution of fresh craters on Ganymede. There is, however, a much higher probability that the relative depths are uniformly distributed between 0 (fresh) and 1 (completely infilled). This distribution is consistent with an infilling process that is relatively constant with time, such as aeolian deposition. Assuming that Ganymede represents a close 'airless' analogue to Titan, the difference in depths represents the first quantitative measure of the amount of modification that has shaped Titan's surface, the only body in the outer Solar System with extensive surface-atmosphere exchange.

Implications↗

NASA NTRS2007

Cassini Observes the Active South Pole of Enceladus

Cassini has identified a geologically active province a the south pole of Saturn's moon Enceladus. The shape of Enceladus suggests a possible intense heating epoch in the past by capture into a 1:4 secondary spin/orbit resonance.

Porco, C. C.↗

NASA NTRS2005

Dependence of Surface Contrast on Emission Angle in Cassini ISS 938-nm Images of Titan

Titan, the largest of Saturn s moons, is one of the most difficult solid surfaces in the Solar System to study. It is shrouded in a thick atmosphere with fine haze particles extending up to 500 km. [1] The atmosphere itself is rich in methane, which allows clear viewing of the surface only through narrow "windows" in the methane spectrum. Even in these methane windows, the haze absorbs and scatters light, blurring surface features and reducing the contrast of images. The haze optical depth is high at visible wavelengths, and decreases at longer (infrared) wavelengths. [2]

Fussner, S.↗

NASA NTRS2005

Distant Secondary Craters and Age Constraints on Young Martian Terrains

Are small (less than approx. 1 km diameter) craters on Mars and the Moon dominated by primary impacts, by secondary impacts of much larger primary craters, or are both primaries and secondaries significant? This question is critical to age constraints for young terrains and for older terrains covering small areas, where only small craters are superimposed on the unit. If the martian rayed crater Zunil is representative of large impact events on Mars, then the density of secondaries should exceed the density of primaries at diameters a factor of ~1000 smaller than that of the largest contributing primary crater. On the basis of morphology and depth/diameter measurements, most small craters on Mars could be secondaries. Two additional observations (discussed below) suggest that the production functions of Hartmann and Neukum predict too many primary craters smaller than a few hundred meters in diameter. Fewer small, high-velocity impacts may explain why there appears to be little impact regolith over Amazonian terrains. Martian terrains dated by small craters could be older than reported in recent publications.

McEwen, A.↗

NASA NTRS2005

Cassini Imaging Results at Titan

The Cassini Imaging Science Subsystem (ISS) images show striking albedo markings on the surface of Titan. In equatorial regions the albedo patterns have high contrast and exhibit prominent lineaments and linear/angular boundaries suggestive of tectonic influences or fracturing of brittle surficial materials. There are intriguing dark curving lines near the south pole. Here we present several working hypotheses to explain these patterns. We also briefly summarize atmospheric science results.

McEwen, A.↗

NASA NTRS2004

Global Distribution of Active Volcanism on Io as Known at the End of the Galileo Mission

Hot spots are manifestations of Io s mechanism of internal heating and heat transfer. Therefore, the global distribution of hot spots and their power output has important implications for how Io is losing heat. The end of the Galileo mission is an opportune time to revisit studies of the distribution of hot spots on Io, and to investigate the distribution of their power output.

Lopes, Rosaly M. C.↗

NASA NTRS2002

Galileo SSI Observations of Io During Orbits C30 I33

New Galileo SSI imaging of Io from orbits C30 I33 will be presented. The aging Galileo spacecraft continues to produce spectacular new results, including the tallest volcanic plume yet found on Io. Additional information is contained in the original extended abstract.

Keszthelyi, L.↗

NASA NTRS2000

New Results on Io's Color and Composition

Galileo's recent high-resolution imaging provides new insights into the nature of Io's colorful surface, shedding light on the composition and origin of pyroclastic deposits and suggesting that Io's mysterious green spots are due to coating or alteration of silicate lavas.

Geissler, P.↗