| Piú viste - Asteroids and Comets |
Comets-Wild_2-00.jpgApproaching Wild 2 (1)60 visiteCaption NASA originale:"This image was taken during the close approach phase of Stardust's Jan 2, 2004 flyby of comet Wild 2. It is a distant side view of the roughly spherical comet nucleus. One hemisphere is in sunlight and the other is in shadow analogous to a view of the quarter moon. Several large depressed regions can be seen. Comet Wild 2 is about 5 Km (3,1 miles) in diameter".
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EROS-G-TouchDown.jpg433 Eros: 4 years after the "touch-down"!60 visiteCaption da "NASA - Picture of the Day" del 12.02.2005:"On 12 February, 2001, the NEAR-Shoemaker spacecraft gently touched-down on the the surface of Eros - the first ever landing on an asteroid. During the descent, the spacecraft's camera recorded successive images of the diminutive world's surface, revealing fractured boulders, dust filled craters, and a mysterious collapsed channel. The last frame, seen in the above montage at the far left, was taken at a range of 128 meters. Expanded in the inset, it shows surface features a few centimeters across. Stereo experimenter Patrick Vantuyne, constructed this montage from the final images in the landing sequence, carefully identifying the overlapping areas in successive frames. Frames which overlap were taken by the spacecraft from slightly different viewpoints, allowing Vantuyne to construct close-up stereo images of the surface of asteroid 433 Eros".
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Comets-Schwassmann_Wachmann_1-00.jpgComet Schwassmann-Wachmann I and two asteroids60 visiteSchwassmann-Wachmann 1 (its nucleus is about 30 Km in diameter and is too small to be resolved by the SST while the micron-sized dust grains in the coma and tail stream out away from the Sun) is thought to be a member of a relatively new class of objects called "Centaurs," of which 45 objects are known. These are small icy bodies with orbits between those of Jupiter and Neptune. Astronomers believe that Centaurs are recent escapees from the Kuiper Belt, a zone of small bodies orbiting in a cloud at the distant reaches of the Solar System. Two asteroids, 1996 GM36 (left) and 5238 Naozane (right) were serendipitously captured in the comet image. Because they are closer to us than the comet and have faster orbital velocities, they appear to move relative to the comet and background stars, thereby producing a slight elongated appearance. The SST data have allowed astronomers to use thermal measurements, which reduce the uncertainties of visible-light albedo (reflectivity) measurements, to determine their size.
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Mathilde-PIA02494.jpgMathilde and Eros: C-Type and S-Type60 visiteCaption NASA originale:"In this montage, Mathilde (at left) and Eros (at right) are shown at the same scale, as they were imaged by NEAR Shoemaker from about 1.800 Km on June 27, 1997, and February 12, 2000, respectively. Mathilde is 56 Km across and Eros is 33 Km long and 13 Km wide. However, Mathilde's brightness is greatly exaggerated for viewing purposes - it's actually 6 times darker than Eros, with about the same reflectivity as soot! In a scheme that reflects how asteroids have historically been a topic for astronomy, not geology, they are classified into groups based on their colors as observed through telescopes. The 2 major classes of asteroids are called S-Types and C-Types. S-Types, whose colors are consistent with "stony" or rocky compositions, prevail among asteroids that orbit closer to the Sun than the mid-point of the asteroid belt. Eros and the 2 asteroids encountered briefly by the Galileo spacecraft on its way to Jupiter - Gaspra and Ida - are all S-Types. C-Types like Mathilde have a dark gray color consistent with a "carbonaceous" composition, rich in carbon compounds and other dark materials. They prevail in the outer part of the asteroid belt".
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Comets-Halley-30155.jpgThe Halley Comet, from Giotto60 visiteCaption ESA originale:"A composite image of the nucleus of comet Halley. This image is composed of 68 images of varying resolution. The data at the brightest point on the nucleus is at the highest resolution (50 m).
The Sun comes from 30° above the horizontal to the left and is 17° behind the image plane (observation phase angle of 107°). The night side of the nucleus can be seen silhouetted against a background of bright dust in the far-field. Jets can be seen originating from 2 regions on the nucleus. Structure can be seen within the jets. A bright area is seen within the night side of the nucleus. We believe this to be a hill or mountain approximately 500 mt high. Other surface details can be seen in the illuminated region".
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Tempel1-XXX-streakoflight.jpgSpace Fireworks...60 visiteCaption NASA originale:"...In the almost 2 hours of time that elapsed during the imaging of the comet, its position changed against the background stars. When all of the images of the motion are added together, the resulting streak of light is shown in the image above. Starting from the left, the comet was its natural brightness. The streak brightens significantly in the middle, immediately after impact of the probe".
Nota: i primi resoconti sui risultati scientifici dell'esperimento ci dicono che la NASA ha "scoperto" che sulla superficie della cometa Tempel-1 c'era (c'è) uno strato di polvere simile al borotalco, ergo più sottile di quanto ci si aspettasse. Inutile dire che, se messo in questi termini, il significato dell'esperimento va ad esaurirsi in un qualcosa che fa solo sorridere (di imbarazzo).
La realtà è molto più complessa e coinvolge la natura, la struttura e la composizione dei cd. "corpi cometari" in rapporto agli altri "corpi rocciosi" presenti nel Sistema Solare...
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Tempel1-Y.jpgThe South-Pole of Tempel-1 and the impact area60 visiteDa "NASA - Picture of the Day" del 6 Luglio 2005:"This diverse landscape is the surface of comet Temple-1's nucleus as seen by the Deep Impact probe's Impactor Targeting Sensor. Within minutes of recording the rugged view, the landscape had changed dramatically though, as the impactor smashed into the surface near the two large, half kilometer-sized craters at picture center. Indications are that the probe penetrated well below the surface before vaporizing, sending a relatively narrow plume of debris blasting back into space. Researchers are still speculating on the final size of the crater produced by the July 4th comet crash, but material continues to spew from the impact site and has caused the faint comet to brighten significantly. Determining the crater dimensions and analyzing the debris ejected from the comet's interior will provide premier insights into the formation of comet Tempel 1, a primordial chunk of our own Solar System".
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Itokawa-3.jpgItokawa and Hayabusa's shadow60 visiteDi asteroidi dalla forma bizzarra ne abbiamo visti davvero molti, ma mai così curiosi quanto Itokawa. Questa immagine, che peraltro possiede una definizione davvero ottima, ci mostra l'ombra della Sonda Hayabusa che si staglia, perfettamente definita, sul versante di Itokawa illuminato dal Sole.
Ed ora, qualche informazione su Hayabusa direttamente dall'Agenzia Spaziale Giapponese:"HAYABUSA's return trip from Earth to Itokawa is 2 billion kilometres long. Needless to say, such a long journey requires a large amount of fuel. HAYABUSA is the first long-distance interplanetary probe to use an ion engine as its main propulsion device.
Traditionally, propulsion occurs when gas is emitted at high speed. Until now, the main form of propulsion has consisted of super-heated gases created by burning fuel with an oxidant. An ion engine, in contrast, gets thrust from ionized gas accelerated by electricity. Therefore, it can accelerate much faster than by traditional propulsion, and only requires a tenth of the fuel.".
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Itokawa-10.jpgSurface details (3)60 visite(B) Taking advantage of the observations made with the onboard instruments, sufficiently detailed information about the sampling sites has been obtained, and the relation between the potential samples and the spectroscopic data has been correctly correlated. As a technology demonstration mission, Hayabusa has already finished the preliminary steps towards the primary sample and return goal. These samples will provide important scientific clues concerning the puzzlingly inconsistent correlations between S-type asteroids and ordinary chondrites, and lead to an improved understanding of the space weathering effect, which may clarify our understanding of the early Solar System and Earth.
(C) Combinations of the Itokawa images along with spacecraft navigation information has enabled shape and gravity models to be numerically defined. The Science Team has started to study and identify the special mechanisms that can move boulders and regolith in the ultra-low gravity environment associated with small objects.
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Comets-Comet_SWAN-3.jpgComet "SWAN"60 visiteDa "NASA - Picture of the Day" del 4 Ottobre 2006:"A newly discovered comet has brightened enough to be visible this week with binoculars. The picturesque comet is already becoming a favored target for northern sky imagers. Pictured above just last week, Comet SWAN showed a bright blue-green coma and an impressive tail. Comet C/2006 M4 (SWAN) was discovered in June in public images from the Solar Wind Anisotropies (SWAN) instrument of NASA and ESA's Sun-orbiting SOHO spacecraft. Comet SWAN, near magnitude six, will be visible with binoculars in the North-Eastern sky not far from the Big Dipper over the next few days before dawn. The comet is expected to reach its peak brightness this week. Passing its closest to the Sun two days ago, Comet SWAN and will be at its closest to the Earth toward the end of this month. Comet SWAN's unusual orbit appears to be hyperbolic, meaning that it will likely go off into interstellar space, never to return".
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EnckeCometTailRipoff_movie_short.gifComet Encke encounters a CME60 visiteCaption NASA:"Swinging inside the orbit of Mercury, on April 20th, 2007, periodic comet Encke encountered a blast from the Sun in the form of a Coronal Mass Ejection (CME). When CMEs, enormous clouds of energetic particles ejected from the Sun, slam into Earth's magnetosphere, they often trigger auroral displays.
But in this case, the collison carried the tail of the comet away.
The tail was likely ripped off by interacting magnetic fields rather than the mechanical pressure of the collision.
This a GIF-movie showing the remarkable event as recorded by the Heliospheric Imager onboard the STEREO A spacecraft. In the movie, the time between frames is about 45 minutes, while the frames span about 14x20 MKM at the distance of the comet. Of course, similar collisions have happened before as the ancient comet loops through its 3,3 year solar orbit. So don't worry, Encke's tail will grow back!".MareKromium
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Comets-Comet_Holmes-UV.gifComet 17-P-Holmes60 visiteCaption NASA, da "NASA - Picture of the Day" del 30 Ottobre 2007:"Go outside tonight and see Comet Holmes.
No binoculars or telescopes are needed -- just curiosity and a sky map.
Last week, Comet 17P/Holmes underwent an unusual outburst that vaulted it unexpectedly from obscurity into one of the brightest comets in recent years.
Sky enthusiasts from the Northern Hemisphere have been following the comet's progress closely. Pictured above Quebec, Canada, the coma of Comet Holmes has been noticeably expanding over the past few days. In the above picture, an image of Jupiter has been placed artificially nearby to allow for a comparison of angular sizes.
Jupiter has been scaled to the size it would appear at the current location of Comet Holmes. How Comet Holmes will further evolve is unknown, with one possibility being that the expanding gas cloud that started from its recent outburst will slowly disperse and fade".MareKromium
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