MESSENGER ha raggiunto l’orbita di Mercurio

[frankyone]

Sito ufficiale della missione: MESSENGER Web Site

La sonda Messenger della NASA alle 9 pm (EDT) di giovedì è riuscita ad entrare in orbita al pianeta Mercurio, il pianeta più interno del nostro sistema solare.

Un entusiasta Charles Bolden, Amministratore della NASA, ha dichiarato che : “Questa missione continuerà a rivoluzionare la nostra comprensione di Mercurio nell’anno a venire. Messenger è l’esempio di come lo sforzo degli scienziati stia spingendo sempre più i confini della conoscenza umana”.

Alle 9:10 EDT gli scienziati hanno avuto conferma dai dati telemetrici di Messenger del positivo ingresso nell’orbita del pianeta Mercurio.
Dai dati di telemetria e’ stato possibile verificare che, alle ore 8:45 EDT, Messenger abbia attivato per circa 15 minuti i suoi retrorazzi rallentando la sua velocità di 1929 Mph, consentendogli un positivo ingresso nell’orbita del pianeta e ponendo così fine ad un viaggio di 4,9 miliardi di miglia raggiungendo un pianeta distante dalla Terra 96 milioni di miglia.

Messenger è stato lanciato più di 6 anni e mezzo fa ed essere riusciti a fargli raggiungere l’orbita di Mercurio rappresenta un grosso traguardo vista l’enorme mole di lavoro richiesta per l’elaborazione della navigazione e del controllo di missione che e’ stato richiesto a tutti i componenti delle squadre di lavoro coinvolte.

Gli ingegneri di missione saranno ora, e nelle prossime settimane, impegnati a verificare che gli strumenti della navicella spaziale siano operativi e funzionanti. Se non saranno segnalati malfunzionamenti o guasti, il 4 Aprile verrà attivata la prima fase scientifica della missione.

Messenger è una creatura di APL, Applied Physics Laboratory, che ne ha curato la progettazione e la costruzione.
APL gestisce la missione per conto del Science Mission Directorate della NASA

Fonte : NASA











NASA - MESSENGER - Unlocking the Secrets of Mercury

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First Image Ever Obtained from Mercury Orbit

At 5:20 am EDT on Mar. 29, 2011, MESSENGER captured this historic image of Mercury. This image is the first ever obtained from a spacecraft in orbit about the Solar System's innermost planet. Over the subsequent six hours, MESSENGER acquired an additional 363 images before downlinking some of the data to Earth. The MESSENGER team is currently looking over the newly returned data, which are still continuing to come down.

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington



NASA - First Image Ever Obtained from Mercury Orbit

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A First Look at Terrain Near Mercury's North Pole

This WAC image showing a never-before-imaged area of Mercury’s surface was taken from an altitude of 450 km (280 miles) above the planet during the spacecraft’s first orbit with the camera in operation. The area is covered in secondary craters made by an impact outside of the field of view. Some of the secondary craters are oriented in chain-like formations.

This image was taken during MESSENGER’s closest approach to the sunlit portion of the surface during this orbit, just before crossing over the terminator. The oblique illumination by the Sun causes the long shadows and accentuates topography. The highly elliptical orbit of MESSENGER brings the spacecraft down to a periapsis (MESSENGER’s closest approach to Mercury) altitude of 200 km (125 miles) and out to an apoapsis (MESSENGER’s farthest distance from Mercury) altitude of 15,000 km (9300 miles).

Date acquired: March 29, 2011



MESSENGER's Wide-Angle Camera

The wide-angle camera (WAC) is not a typical color camera. It can image in 11 colors, ranging from 430 to 1020 nm wavelength (visible through near-infrared). It does this with a filter wheel: the 11 narrow-band filters (plus one clear filter) are mounted onto a wheel that can be rotated to allow the camera to capture an image through each filter. In this image the 1000 nm, 750 nm, and 430 nm filters are displayed in red, green, and blue, respectively. Several craters appear to have excavated compositionally distinct low-reflectance (brown-blue in this color scheme) material, and the bright rays of Hokusai crater to the north cross the image. During MESSENGER’s orbital operations, we will typically use just eight of the WAC's filters. This decision was made to reduce the amount of data that must be stored on the spacecraft’s solid-state recorder before the information can be downlinked. It’s also quicker than cycling through all 11 filters – the spacecraft is moving rapidly over the surface, and there isn't much time to image the same spot on the surface 11 times over before moving to the next area of interest. The sets of color images will help us learn about the variation in composition from place to place on the planet. For example, some minerals such as olivine and pyroxene often absorb more light at longer wavelengths than at shorter ones, so we’ll be looking for their signatures in the reflectance spectra derived from each eight-color set. WAC images will be used in coordination with the Mercury Atmospheric and Surface Composition Spectrometer (MASCS), a hyperspectral instrument that provides reflectance information at many more wavelengths, but only for one spot on the surface at a time.

Date acquired: March 29, 2011



Exploring the Rays of Debussy

Bright rays, consisting of impact ejecta and secondary craters, spread across this NAC image and radiate from Debussy crater, located at the top. The image, acquired yesterday during the first orbit for which MDIS was imaging, shows just a small portion of Debussy's large system of rays in greater detail than ever previously seen. Images acquired during MESSENGER's second Mercury flyby showed that Debussy's rays extend for hundreds of kilometers across Mercury's surface. Debussy crater was named in March 2010, in honor of the French composer Claude Debussy (1862-1918).

Date acquired: March 29, 2011



An Annotated Guide to the First Orbital Image

This historic first orbital image of Mercury was acquired 37 years to the day after Mariner 10's historic first flyby of the innermost planet. Labels have been added to indicate several craters that were named based on Mariner 10 images, as well as Debussy, Matabei, and Berkel, which were named based on MESSENGER flyby images. The surface contained in the white lines is terrain previously unseen by spacecraft, and the star indicates the location of the south pole.

Date acquired: March 29, 2011

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington



Machaut is the name of a crater, approximately 100 kilometer (60 mile) in diameter, first seen under high-sun conditions by Mariner 10 in the 1970s. The crater is named for the medieval French poet and composer Guillaume de Machaut. This NAC image shows an amazing new view of Machaut taken during MESSENGER’s second flyby of Mercury on Oct. 6, 2008. The slanting rays of the Sun cast shadows that reveal numerous small craters and intricate features. The largest crater within Machaut appears to have been inundated by lava flows similar to those that have filled most of the floor of the larger feature. The adjacent, slightly smaller crater was formed at a later time and excavated material below the lava-formed surface. MESSENGER science team members will also be studying the shallow ridges that crisscross Machaut’s floor.



About 58 minutes before MESSENGER’s closest approach to Mercury on Oct. 6, 2008, the Narrow Angle Camera captured this close-up image of a portion of Mercury’s surface -- imaged by spacecraft for the first time during this flyby. The features in the foreground, near the right side of the image, are close to the terminator, the line between the sunlit dayside and dark night side of the planet, so shadows are long and prominent. Two very long scarps, or cliffs, are visible in this region, and the scarps appear to crosscut each other. The easternmost scarp also cuts through a crater, showing that it formed after the impact that created the crater. Other neighboring impact craters, such as in the upper left of this image, appear to be filled with smooth plains material.

[frankyone]

I crateri senza creste al centro sono i più antichi perchè all'epoca il pianeta era ancora fluido,sicchè quando una meteorite ci cadeva sopra il magma che fuoriusciva dalla zona dell'impatto livellava tutto.

Quelli con il picco centrale sono più recenti quando la crosta del pianeta ormai era solidificata: quando il metorite colpiva la superficie si fluidificava solo la zona circostante l'impatto e si formava una cresta centrale esattamente allo stesso modo di quanto succede con una goccia d'acqua che cade in un recipiente contenente acqua,cioè si forma un promontorio,che in questo caso però solidifica creando una piccola montagnola centrale.