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| Piú viste - Mercury |
ZZ-Mercury-Rupes-Terror_Rupes-PIA17881-PCF-LXTT-IPF-01.jpgTerror Rupes (EDM - Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/Italian Planetary Foundation)78 visiteIn this picture, we can better see the Southern Mercurian Relief known as "Terror Rupes": it is the long, Cliff-like Landform visible right in the middle of the frame. Terror Rupes is one of Mercury's most prominent Lobate Scarps, and it was so named after the HMS (---> Her Majesty's Ship) Terror: an eighteenth-century warship that, later, participated in Scientific Polar Explorations.
Date acquired: February, 4th, 2012
Image Mission Elapsed Time (MET): 236853865
Image ID: 1353252
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 69,30° South
Center Longitude: 96,00° East
Solar Incidence Angle: 80,3° (meaning that the Sun, at the time that the picture was taken, was about 9,7° above the imaged Local Mercurian Horizon)
Emission Angle: 50,9°
Sun-Mercury-Messenger (or "Phase") Angle: 114,5°
This picture (which is a crop taken from an Original NASA - MESSENGER Spacecraft's b/w and NON-Map-Projected image published on the NASA - Planetary Photojournal with the ID n. PIA 17881) has been additionally processed, contrast enhanced, Gamma corrected, magnified to aid the visibility of the details and then colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - MESSENGER Spacecraft and then looked outside, towards the Surface of Mercury), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among other things, the existence of different Elements (Minerals) present on the Surface of Mercury, each having a different Albedo (---> Reflectivity) and Chemical Composition.MareKromium
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ZF-Mercury_s South Pole-PIA02415_modest.jpgMercury's South Pole77 visite3) vaporizzazione delle rocce causata da impatti con altri corpi celesti (meteore o comete).
Ma leggiamo ora cosa ci dice la NASA a proposito del fly-by del Mariner 10 nei pressi del suo Polo Sud: "...After passing Mercury the first time and making a trip around the Sun, Mariner 10 again flew by Mercury on September 21, 1974. This encounter brought the spacecraft in front of Mercury in the southern hemisphere. In this frame south is down, the South Pole is located on the right hand edge of the large crater that has only its rim sticking up into the light ("Chao Meng Fu" crater). When this frame was acquired, Mariner 10 was about 83.000 Km from Mercury".
Un'ultima annotazione riguarda i gas presenti nella sottilissima esosfera di Mercurio. Non possiamo parlare di un'atmosfera vera e propria poichè le molecole dei vari elementi che si trovano intorno al Pianeta sono così poche che non riescono neppure a collidere fra loro, come invece accade su Venere, Marte e la Terra stessa, ma si limitano a "rimbalzare" sulla sua superficie!
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ZP-Mercury-PIA10394.jpgFirst "Laser Altimetry" for Mercury77 visiteCaption NASA:"At top center is the first Laser Altimeter Profile of Mercury's topography, taken by MESSENGER's Mercury Laser Altimeter (MLA) instrument during the Spacecraft's flyby of Mercury on January 14, 2008.
At bottom center is the MLA ground projected onto a mosaic of radar images obtained by Harmon and others at the Arecibo Observatory in Puerto Rico.
The interval during which MESSENGER was sufficiently close to the Planet to be within measurement range of the MLA was when the Spacecraft was on the night side, so there are no corresponding images of this Region acquired by MESSENGER during this flyby; this Region was also unseen by Mariner 10.
The length of the profile is about 3200 Km (about 2000 miles), and the dynamic range in elevation across the profile is about 5 Km (about 3 miles). The profile sampled numerous craters and basins. The vertical exaggeration in the figure is equal to 105:1.
At top left is a photograph of the MLA flight unit".MareKromium
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ZZ-Mercury-Terminator-PIA10939.jpgSveinsdóttir Crater and Beagle Rupes (natural colors; credits: Lunexit)77 visiteNamed for Júlíana Sveinsdóttir, an Icelandic painter and textile artist, Sveinsdóttir Crater superimposed by Beagle Rupes is a distinctive feature on Mercury's landscape. Unusually elliptical in shape, the Crater was produced by the impact of an object that hit Mercury’s Surface obliquely. More than 600 Km (about 370 miles) long and one of the largest fault scarps on the Planet, Beagle Rupes marks the surface expression of a large thrust fault believed to have formed as Mercury cooled and the entire planet shrank. Beagle Rupes crosscuts Sveinsdóttir Crater and has uplifted the easternmost portion (right side portion) of the crater floor by almost a kilometer, indicating that most of the fault activity at Beagle Rupes occurred after the impact that created Sveinsdóttir. Crosscutting relationships such as this are used to understand the sequence in time of the different processes that have affected Mercury’s evolution.
Date Acquired: January 14, 2008
Image Mission Elapsed Time (MET):108830230
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Resolution: 0,77 Kilometers/pixel (0,48 miles/pixel)
Scale: This image is about 780 Km (approx. 490 miles) across; Sveinsdóttir crater is about 120 by 220 Km (appprox. 75 by 140 miles)
Spacecraft Altitude: about 30.300 Km (approx. 18.800 miles)
MareKromium
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ZZ-Mercury-Limb-CN0131766564M.pngA Small Crater Makes a Bright Impact (natural colors; credits: Lunexit)77 visiteDate Acquired: October 6, 2008
Image Mission Elapsed Time (MET): 131766564
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Resolution: 410 meters/pixel (0,25 miles/pixel) in the lower right corner of the image
Scale: The bright crater is about 30 Km in diameter (approx. 19 miles)
Spacecraft Altitude: about 16.000 Km (about 9900 miles)
Of Interest: In both the optical navigation images and the full-planet Wide Angle Camera (WAC) approach frame, a bright feature is clearly visible in the northern portion of the crescent-shaped Mercury. This NAC image resolves details of this bright feature, showing that it surrounds a small crater about 30 Km (approx. 19 miles) in diameter, seen nearly edge-on. Presumably, the bright material was ejected from this small crater, which apparently formed relatively recently in Mercury’s past, because Mercury’s surface materials tend to darken with time. The brilliant ejecta are so bright compared with the neighboring surface that Earth-based telescopic observations also detected this feature, despite its being associated with such a small crater.MareKromium
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ZZ-Mercury-Limb-CW0131772818A_web.jpgMercury, during MESSENGER's 2nd Fly-By (natural, but enhanced colors; credits: Lunexit)77 visiteDate Acquired: October 6, 2008
Image Mission Elapsed Time (MET): 131772818
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC Filter: 1 (700 nanometers)
Resolution: 2,6 Km/pixel (about 1,6 miles/pixel)
Scale: The left side of the image is about 2700 Km tall (approx. 1700 miles)
Spacecraft Altitude: about 15.000 Km (approx. 9300 miles)
Of Interest: One week ago, no spacecraft had ever seen the majority of the surface visible in this image. Today, one week after MESSENGER’s successful second Mercury flyby, about 95% of Mercury’s surface has been viewed by spacecraft, resulting in nearly global spacecraft imaging coverage of Mercury’s surface for the first time. This WAC image is just one of 99 in a set of 3 columns by 3 rows by 11 color filters that is being combined into a color mosaic of the departing planet. Kuiper crater, with its bright ejecta rays, is visible on the left edge of the image and was seen by Mariner 10, but most of the terrain east of Kuiper was not. A newly imaged crater with an unusual halo of dark material is visible at about the same latitude but toward Mercury’s limb. The long, bright rays that can be seen extending across the surface emanate from a crater just north of this image.MareKromium
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ZO-Mercury02_Messenger.jpgMessenger's First Look at Mercury's Previously Unseen Side76 visiteCaption NASA:"This image was taken on January 14, 2008, by NASA's MESSENGER Spacecraft at a distance of approx. 17.000 miles following the Spacecraft's closest approach to Mercury. The image shows features as small as 6 miles in size.
Similar to previously mapped portions of Mercury, this Hemisphere appears heavily cratered. It also reveals some unique and distinctive features.
On the upper right is the giant Caloris basin, including its western portions never before seen by spacecraft. Formed by the impact of a large asteroid or comet, Caloris Basin is one of the largest, and perhaps one of the youngest basins in the Solar System". MareKromium
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ZO-Mercury13_Messenger-209132main_color_mercury.jpgMercury in False Colors (credits: NASA)76 visiteOne week ago, the MESSENGER Spacecraft transmitted to Earth the first HR image of Mercury by a spacecraft in over 30 years, since the 3 Mercury flybys of Mariner 10 in 1974 and 1975. MESSENGER's Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS), is equipped with 11 narrow-band color filters, in contrast to the two visible-light filters and one ultraviolet filter that were on Mariner 10's vidicon camera. By combining images taken through different filters in the visible and infrared, the MESSENGER data allow Mercury to be seen in a variety of high-resolution color views not previously possible. MESSENGER’s eyes can see far beyond the color range of the human eye, and the colors seen in the accompanying image are somewhat different from what a human would see.
The color image was generated by combining three separate images taken through WAC filters sensitive to light in different wavelengths; filters that transmit light with wavelengths of 1000, 700, and 430 nnmts (infrared, far red, and violet, respectively) were placed in the red, green, and blue channels, respectively, to create this image. The human eye is sensitive across only the wavelength range 400 to 700 nanometers. Creating a false-color image in this way accentuates color differences on Mercury's surface that cannot be seen in the single-filter, black-and-white images released last week.
MareKromium
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ZO-Mercury20_Messenger-PIA10171.jpgRendez-Vous with Mercury76 visiteAs the MESSENGER spacecraft approached Mercury for its first flyby, the Narrow Angle Camera, part of the Mercury Dual Imaging System (MDIS) instrument, acquired a series of images of the Planet in support of spacecraft navigation.
The 9 images shown here were taken from January 9 to 13, 2008, as MESSENGER closed to between 2,7 MKM and 760.000 Km (1,7 MMs and 470.000 miles) from Mercury. (...)
At the beginning of the image sequence, Mercury was no more than a bright crescent in the blackness of space. As MESSENGER drew closer, surface features began to be resolved. The image from January 13 (bottom right) has the highest spatial resolution of this sequence (20 Km/pixel, such as about 12 miles/pixel).
In this image, bright markings are visible, and impact craters can be seen near the Terminator.MareKromium
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ZM-N-TheSwingby-GIF.gifThe Swing-by (or Gravity Assist): acceleration (GIF-Movie)76 visiteIn Meccanica Orbitale ed in Ingegneria Aerospaziale, si definisce "Fionda Gravitazionale" l'utilizzo della gravità di un pianeta per alterare il percorso e la velocità di un veicolo spaziale.
Questa tecnica è comunemente usata per raggiungere i Pianeti Esterni, che altrimenti sarebbero proibitivi, se non impossibili, da raggiungere con le tecnologie attuali (essenzialmente per motivi di costi e tempi troppo lunghi).
Questa tecnica è anche chiamata gravity-assist e la si può utilizzare con profitto solo con pianeti dotati di grande massa.
L'idea della Fionda Gravitazionale fu sviluppata già negli anni 1961-63 dal matematico Michael Minovitch. Inizialmente fu ritenuta solamente una curiosità, in quanto all'epoca sarebbe stato molto difficile poter avere delle applicazioni pratiche della teoria poiché era necessario dover attendere delle particolari disposizioni dei pianeti rispetto alla Terra ed era altresì richiesta una grandissima precisione.
Tuttavia, nel 1973, Giuseppe Colombo propose alla NASA l'uso di una Fionda Gravitazionale con Venere per far incontrare la sonda Mariner 10 con Mercurio ben 3 volte e la soluzione proposta funzionò perfettamente. Da allora, essa è stata ripetuta molte altre volte. Ad esempio, alcune delle sonde che hanno utilizzato la Fionda Gravitazionale sono state le Voyager 1 e 2, le Sonde Pioneer 10 ed 11, e quindi le Sonde Ulisse, Galileo, Cassini-Huygens e, ultima ma non meno importante, la Sonda Messenger.
Il modo più semplice per far andare una sonda da un pianeta ad un altro è quello di utilizzare un Trasferimento alla Hohmann, ovvero far percorrere alla sonda un'orbita ellittica con la Terra al perielio e l'altro pianeta all'afelio.
Se lanciato nel momento adeguato (e cioè all'interno della cd "Finestra di Lancio Ottimale"), il veicolo spaziale arriverà all'afelio proprio quando il pianeta starà passando in quei pressi.
Questo tipo di trasferimento è comunemente usato per muoversi attorno alla Terra, o dalla Terra alla Luna e/o dalla Terra a Marte.
Ma il Trasferimento alla Hohmann usato per raggiungere pianeti esterni richiederebbe tempi lunghi ed un considerevole "Delta V" (esso esprime la quantità di propellente necessaria ad eseguire una manovra orbitale).
Ed è proprio in questi casi che l'effetto fionda è usato più frequentemente. Ad esempio, invece di raggiungere Saturno con un Trasferimento alla Hohmann, si raggiunge Giove con quel sistema e poi si sfrutta la sua gravità (Gravity-Assist) per raggiungere Saturno.
(da Wikipedia - Voce "Fionda Gravitazionale" - note e commenti ulteriori: Dr Paolo C. Fienga)MareKromium
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ZU-PIA12051.jpgGlobal Map of Mercury76 visiteMESSENGER's two flybys of Mercury in 2008 have greatly increased the portion of the Planet's Surface that has been imaged by spacecraft, from approximately 45% coverage obtained by Mariner 10 to about 90% coverage following the second flyby.
This significant increase in imaging coverage is enabling global studies of Mercury's Surface for the first time. MESSENGER team members recently published an article in the 1st of May issue of the "Science" Magazine that utilizes this new global view to examine the evolution of Mercury's crust. This recent work was also featured in a NASA media teleconference, and the top image shown here was presented during that teleconference.
Both images are orthographic map projections of Mercury created with WAC enhanced-color images. The orthographic projection produces a view that has the perspective that one would see from deep space. The WAC enhanced color uses a statistical analysis of images from all 11 WAC filters to highlight subtle differences in the crustal rocks on Mercury's Surface. For other examples and discussion of enhanced color images, see previous releases of the departure view from Mercury flyby 2, Rudaki Plains, Thakur Crater and Caloris Basin.
The top view uses images from Mercury flyby 1, with the thin crescent of Mercury imaged during approach forming the right portion of the globe and the fuller departure view showing Caloris Basin forming the left side and majority of the view.
The black strip between the approach and departure images is a portion of Mercury's Surface not viewed by MESSENGER during the flybys. Similarly, the approach and departure images obtained during Mercury flyby 2 yielded the bottom view.
The top and bottom projections are centered on 180° and 0° Longitude, respectively.
Date Acquired: January 14, 2008, and October 6, 2008
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Scale: Mercury’s diameter is about 4880 Km (approx. 3030 miles)MareKromium
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ZW-Mercury-PIA12397.jpgMercury76 visiteToday (December, 15th, 2009), the first High-Resolution Global Map of Mercury was made publicly available. Members of the MESSENGER team and experts from the U. S. Geological Survey (USGS) used images from MESSENGER's three Mercury flybys and from the Mariner 10 Mission in 1974-75 to create a Global Mosaic that covers 97,7% of Mercury's Surface at a resolution of 500 meters/pixel (0,31 miles/pixel).
The above image shows the full global Mercury mosaic but at a greatly reduced scale of only 5% of the HR version. The full HR mosaic by can be seen at the USGS Map-a-Planet website.
Date Mercury Fly-By 1: January 14, 2008
Date of Mercury Fly-By 2: October 6, 2008
Date of Mercury Fly-By 3: September 29, 2009
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Scale: Mercury's diameter is approx. 4880 Km (such as about 3030 miles)MareKromium
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