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TOPIC: Neptune


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RE: Neptune
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Title: Uranus and Neptune: Shape and Rotation
Authors: Ravit Helled, John D. Anderson, Gerald Schubert

Both Uranus and Neptune are thought to have strong zonal winds with velocities of several hundred meters per second. These wind velocities, however, assume solid-body rotation periods based on Voyager 2 measurements of periodic variations in the planets' radio signals and of fits to the planets' magnetic fields; 17.24h and 16.11h for Uranus and Neptune, respectively. The realisation that the radio period of Saturn does not represent the planet's deep interior rotation and the complexity of the magnetic fields of Uranus and Neptune raise the possibility that the Voyager 2 radio and magnetic periods might not represent the deep interior rotation periods of the ice giants. Moreover, if there is deep differential rotation within Uranus and Neptune no single solid-body rotation period could characterise the bulk rotation of the planets. We use wind and shape data to investigate the rotation of Uranus and Neptune. The shapes (flattening) of the ice giants are not measured, but only inferred from atmospheric wind speeds and radio occultation measurements at a single latitude. The inferred oblateness values of Uranus and Neptune do not correspond to bodies rotating with the Voyager rotation periods. Minimisation of wind velocities or dynamic heights of the 1 bar isosurfaces, constrained by the single occultation radii and gravitational coefficients of the planets, leads to solid-body rotation periods of ~16.58h for Uranus and ~17.46h for Neptune. Uranus might be rotating faster and Neptune slower than Voyager rotation speeds. We derive shapes for the planets based on these rotation rates. Wind velocities with respect to these rotation periods are essentially identical on Uranus and Neptune and wind speeds are slower than previously thought. Alternatively, if we interpret wind measurements in terms of differential rotation on cylinders there are essentially no residual atmospheric winds.

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An icy comet might have smashed into Neptune two centuries ago - that's what scientists have gauged from the latest measurements of gases in the atmosphere of the giant blue planet.
At a meeting this week of the American Astronomical Society in Miami, Florida, Paul Hartogh, project scientist for the Herschel mission, the European Space Agency's infrared observatory satellite, described the mission's first results for the Solar System.

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Carbon monoxide in planet's atmosphere points to icy impact.

Did a large, icy comet smash into Neptune two centuries ago? That's the picture that is emerging from the latest measurements of gases in the atmosphere of the giant blue planet.
At a meeting this week of the American Astronomical Society in Miami, Florida, Paul Hartogh, project scientist for the Herschel mission, the European Space Agency's infrared observatory satellite, described the mission's first results for the Solar System. These include measurements of abnormally high levels of carbon monoxide in Neptune's stratosphere - a possible trace of a comet impact.

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The Wizard's Eye (sometimes called Great Dark Spot 2) is another cyclone on Neptune. It is about one third the diameter of the Great Dark Spot. It received the name "Wizard's Eye" because it looks like an eye.
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Title: Seeing Double at Neptune's South Pole
Authors: S. H. Luszcz-Cook, I. de Pater, M. Adamkovics, H. B. Hammel

Keck near-infrared images of Neptune from UT 26 July 2007 show that the cloud feature typically observed within a few degrees of Neptune's south pole had split into a pair of bright spots. A careful determination of disk centre places the cloud centres at -89.07 0 .06 and -87.84 0.06 degrees planetocentric latitude. If modelled as optically thick, perfectly reflecting layers, we find the pair of features to be constrained to the troposphere, at pressures greater than 0.4 bar. By UT 28 July 2007, images with comparable resolution reveal only a single feature near the south pole. The changing morphology of these circumpolar clouds suggests they may form in a region of strong convection surrounding a Neptunian south polar vortex.

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Astronomers have detected an extraterrestrial cyclone at Neptune's south pole, which may improve our understanding of the violent weather conditions that rage across the distant planet.
It could also help us better understand Neptune's internal structure.
The team of astronomers made the discovery while studying clouds on other planets using the giant 10-metre Keck Telescopes on Mauna Kea, Hawaii.

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Neptune may have eaten a planet and stolen its moon

Neptune may have polished off a super-Earth that once roamed the outer solar system and stolen its moon to boot. The brutal deed could explain mysterious heat radiating from the icy planet and the odd orbit of its moon Triton.
Neptune's own existence was a puzzle until recently. The dusty cloud that gave birth to the planets probably thinned out further from the sun. With building material so scarce, it is hard to understand how Uranus and Neptune, the two outermost planets, managed to get so big.
But what if they formed closer in? In 2005, a team of scientists proposed that the giant planets shifted positions in an early upheaval. In this scenario, Uranus and Neptune formed much closer to the sun and migrated outwards, possibly swapping places in the process.

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Title: Seeing Double at Neptune's South Pole
Authors: S. H. Luszcz-Cook, I. de Pater, M. Adamkovics, H. B. Hammel

Keck near-infrared images of Neptune from UT 26 July 2007 show that the cloud feature typically observed within a few degrees of Neptune's south pole had split into a pair of bright spots. A careful determination of disk centre places the cloud centres at -89.07 0 .06 and -87.84 0.06 degrees planetocentric latitude. If modelled as optically thick, perfectly reflecting layers, we find the pair of features to be constrained to the troposphere, at pressures greater than 0.4 bar. By UT 28 July 2007, images with comparable resolution reveal only a single feature near the south pole. The changing morphology of these circumpolar clouds suggests they may form in a region of strong convection surrounding a Neptunian south polar vortex.

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Galileo knew he had discovered a new planet in 1613, 234 years before its official discovery, according to a new theory by a University of Melbourne physicist and alumnus.

"It has been known for several decades that this unknown star was actually the planet Neptune. Computer simulations show the precision of his observations revealing that Neptune would have looked just like a faint star almost exactly where Galileo observed it" - Professor David Jamieson.

But a planet is different to a star because planets orbit the Sun and move through the sky relative to the stars. It is remarkable that on the night of January 28 in 1613 Galileo noted that the "star" we now know is the planet Neptune appeared to have moved relative to an actual nearby star."
There is also a mysterious unlabeled black dot in his earlier observations of January 6, 1613, which is in the right position to be Neptune.

"I believe this dot could reveal he went back in his notes to record where he saw Neptune earlier when it was even closer to Jupiter but had not previously attracted his attention because of its unremarkable star-like appearance"

If the mysterious black dot on January 6 was actually recorded on January 28, Professor David Jamieson proposes this would prove that Galileo believed he may have discovered a new planet.

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Neptune Trojans
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Title: Neptune Trojans and Plutinos: colours, sizes, dynamics, and their possible collisions
Authors: A.J.C. Almeida, N. Peixinho, A.C.M. Correia

Neptune Trojans and Plutinos are two subpopulations of trans-Neptunian objects located in the 1:1 and the 3:2 mean motion resonances with Neptune, respectively, and therefore protected from close encounters with the planet. However, the orbits of these two kinds of objects may cross very often, allowing a higher collisional rate between them than with other kinds of trans-Neptunian objects, and a consequent size distribution modification of the two subpopulations.
Observational colours and absolute magnitudes of Neptune Trojans and Plutinos show that i) there are no intrinsically bright (large) Plutinos at small inclinations, ii) there is an apparent excess of blue and intrinsically bright (small) Plutinos, and iii) Neptune Trojans possess the same blue colours as Plutinos within the same (estimated) size range do.
For the present subpopulations we analysed the most favourable conditions for close encounters/collisions and address any link there could be between those encounters and the sizes and/or colours of Plutinos and Neptune Trojans. We also performed a simultaneous numerical simulation of the outer Solar System over 1 Gyr for all these bodies in order to estimate their collisional rate.
We conclude that orbital overlap between Neptune Trojans and Plutinos is favoured for Plutinos with large libration amplitudes, high eccentricities, and small inclinations. Additionally, with the assumption that the collisions can be disruptive creating smaller objects not necessarily with similar colours, the present high concentration of small Plutinos with small inclinations can thus be a consequence of a collisional interaction with Neptune Trojans and such hypothesis should be further analysed.

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