Messenger: Die Merkur-Sonde nach Mariner 10

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Re: Messenger Update

Sorry, hier muss ich meinem Unmut Ausdruck verleihen! (Leider werden es die Verantwortlichen nicht lesen...)
W.B.Yeats hat wahrhaftig besseres verdient als diesen unbedeutenden Merkurkrater! Dann lieber gar nichts als sowas.

Tja, der Sinn oder Unsinn von Nomenklaturregeln bei der IAU hat ja schon vielerlei Unmut und Kontroversen ausgelöst. Bei den Kratern auf Merkur hat man sich anscheinend auf Künstler und Schriftsteller festgelegt, und das wird dann anscheinend enzyklopädisch "abgearbeitet":

Bach (214 km)
Beethoven (643 km)
Cervantes (181 km)
Cézanne (75 km)
Chaikowskij (165 km)
Copland (208 km)
Couperin (80 km)
Debussy (85 km)
Dowland (100 km)
Dürer (180 km)
Dvarak (82 km)
.
.
.
Goethe (383 km)
Händel (166 km)
Haydn (270 km)
Heine (75 km)
Hemingway (130 km)
.
.
.
Ibsen (159 km)
Matisse (210 km)
Michelangelo (216 km)
Molière (132 km)
Monteverdi (138 km)
Mozart (270 km)
Ovid (44 km)
Picasso (133 km)
Praxiteles (182 km)
Proust (157 km)
Puccini (70 km)
Purcell (91 km)
.
.
.
Schubert (185 km)
Shakespeare (370 km)
Stravinsky (190 km)
.
.
.
Yeats (100 km)

Größe kann man eben nicht nur in Kilometern messen ...

Mit freundlichen Grüßen,
Peter

 

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Debussy

The extensive rays of Debussy stretch across this image of Mercury's limb. The crater and its rays appear brighter than the surrounding surface for the most part because the crater is relatively young. The excavated materials have not resided on the surface long enough to have been substantially darkened by space weathering.

 

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Re: Messenger Update

Diese Woche gab es eine News Conference mit der Vorankündigung einer ganzen Serie von Artikeln, die jetzt im Science Magazine erscheinen:

Special Collection: MESSENGER Orbits Mercury

In the 30 September 2011 Science, seven Reports present high-resolution images and x-ray data that provide new details about the surface composition of Mercury, as well as the planet's geologic history, and magnetic field.

Hier sind die Abstracts:

The Major-Element Composition of Mercury's Surface from MESSENGER X-ray Spectroscopy

X-ray fluorescence spectra obtained by the MESSENGER spacecraft orbiting Mercury indicate that the planet’s surface differs in composition from those of other terrestrial planets. Relatively high Mg/Si and low Al/Si and Ca/Si ratios rule out a lunarlike feldspar-rich crust. The sulfur abundance is at least 10 times higher than that of the silicate portion of Earth or the Moon, and this observation, together with a low surface Fe abundance, supports the view that Mercury formed from highly reduced precursor materials, perhaps akin to enstatite chondrite meteorites or anhydrous cometary dust particles. Low Fe and Ti abundances do not support the proposal that opaque oxides of these elements contribute substantially to Mercury’s low and variable surface reflectance.

Radioactive Elements on Mercury's Surface from MESSENGER ...

The MESSENGER Gamma-Ray Spectrometer measured the average surface abundances of the radioactive elements potassium (K, 1150 ± 220 parts per million), thorium (Th, 220 ± 60 parts per billion), and uranium (U, 90 ± 20 parts per billion) in Mercury’s northern hemisphere. The abundance of the moderately volatile element K, relative to Th and U, is inconsistent with physical models for the formation of Mercury requiring extreme heating of the planet or its precursor materials, and supports formation from volatile-containing material comparable to chondritic meteorites. Abundances of K, Th, and U indicate that internal heat production has declined substantially since Mercury’s formation, consistent with widespread volcanism shortly after the end of late heavy bombardment 3.8 billion years ago and limited, isolated volcanic activity since.

Flood Vulcanism in the Northern High Latitudes ...

MESSENGER observations from Mercury orbit reveal that a large contiguous expanse of smooth plains covers much of Mercury’s high northern latitudes and occupies more than 6% of the planet’s surface area. These plains are smooth, embay other landforms, are distinct in color, show several flow features, and partially or completely bury impact craters, the sizes of which indicate plains thicknesses of more than 1 kilometer and multiple phases of emplacement. These characteristics, as well as associated features, interpreted to have formed by thermal erosion, indicate emplacement in a flood-basalt style, consistent with x-ray spectrometric data indicating surface compositions intermediate between those of basalts and komatiites. The plains formed after the Caloris impact basin, confirming that volcanism was a globally extensive process in Mercury’s post–heavy bombardment era.

Hollows on Mercury ...

High-resolution images of Mercury’s surface from orbit reveal that many bright deposits within impact craters exhibit fresh-appearing, irregular, shallow, rimless depressions. The depressions, or hollows, range from tens of meters to a few kilometers across, and many have high-reflectance interiors and halos. The host rocks, which are associated with crater central peaks, peak rings, floors, and walls, are interpreted to have been excavated from depth by the crater-forming process. The most likely formation mechanisms for the hollows involve recent loss of volatiles through some combination of sublimation, space weathering, outgassing, or pyroclastic volcanism. These features support the inference that Mercury’s interior contains higher abundances of volatile materials than predicted by most scenarios for the formation of the solar system’s innermost planet.

The Global Magnetic Field of Mercury ...

Magnetometer data acquired by the MESSENGER spacecraft in orbit about Mercury permit the separation of internal and external magnetic field contributions. The global planetary field is represented as a southward-directed, spin-aligned, offset dipole centered on the spin axis. Positions where the cylindrical radial magnetic field component vanishes were used to map the magnetic equator and reveal an offset of 484 ± 11 kilometers northward of the geographic equator. The magnetic axis is tilted by less than 3° from the rotation axis. A magnetopause and tail-current model was defined by using 332 magnetopause crossing locations. Residuals of the net external and offset-dipole fields from observations north of 30°N yield a best-fit planetary moment of 195 ± 10 nanotesla-RM3, where RM is Mercury’s mean radius.

... Spacial Distribution of Planetary Ions near Mercury

Global measurements by MESSENGER of the fluxes of heavy ions at Mercury, particularly sodium (Na+) and oxygen (O+), exhibit distinct maxima in the northern magnetic-cusp region, indicating that polar regions are important sources of Mercury’s ionized exosphere, presumably through solar-wind sputtering near the poles. The observed fluxes of helium (He+) are more evenly distributed, indicating a more uniform source such as that expected from evaporation from a helium-saturated surface. In some regions near Mercury, especially the nightside equatorial region, the Na+ pressure can be a substantial fraction of the proton pressure.

... Transien Bursts of Energetic Electrons in Mercury's Magnetosphere

The MESSENGER spacecraft began detecting energetic electrons with energies greater than 30 kilo–electron volts (keV) shortly after its insertion into orbit about Mercury. In contrast, no energetic protons were observed. The energetic electrons arrive as bursts lasting from seconds to hours and are most intense close to the planet, distributed in latitude from the equator to the north pole, and present at most local times. Energies can exceed 200 keV but often exhibit cutoffs near 100 keV. Angular distributions of the electrons about the magnetic field suggest that they do not execute complete drift paths around the planet. This set of characteristics demonstrates that Mercury’s weak magnetic field does not support Van Allen–type radiation belts, unlike all other planets in the solar system with internal magnetic fields.

Image Gallery Update

Mercury's High-Potassium Diet: The abundance of potassium (K) and thorium (Th) on the surface of Mercury as measured by the MESSENGER Gamma-Ray Spectrometer. These values are compared to similar measurements of the K and Th content of Venus, Earth, the Moon, and Mars. Because K is a volatile element and Th a refractory one, this ratio is a sensitive measure of thermal processes that fractionate elements by volatility. For example, the ratio for the Moon (360) is much lower than that for Earth (3000), reflecting volatile loss during the Moon's formation by a giant impact. The ratio for Mercury is comparable to that of the other terrestrial planets, indicating that Mercury is not highly depleted in volatile elements, ruling out some models for its formation and early history. This finding is supported by the identification of sulfur on the surface by the MESSENGER X-Ray Spectrometer.

 

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MESSENGER Team Presents New Mercury Findings at Planetary Conference

MESSENGER scientists will highlight the latest results on Mercury from MESSENGER observations obtained during the first six months (the first Mercury solar day) in orbit. These findings will be presented October 5 in 30 papers and posters as part of a special session of the joint meeting of the European Planetary Science Congress and the Division for Planetary Sciences of the American Astronomical Society in Nantes, France.

Und noch ein neues Bild in Farbe:

View of a section of the floor and peak-ring mountains of the Raditladi impact basin, including the area in a previous Gallery image. The individual frames in the mosaic are about 20 km wide. The rounded, depressions, called "hollows" are a fascinating discovery of MESSENGER's orbital mission and may have been formed by sublimation of a component of the material when exposed by the Raditladi impact. This image was created by merging high-resolution monochrome images from MESSENGER's Narrow Angle Camera with a lower-resolution enhanced-color image obtained by the Wide Angle Camera.

Date acquired: September 29, 2011

 

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Image gallery

The First Solar Day: After its first Mercury solar day (176 Earth days) in orbit, MESSENGER has nearly completed two of its main global imaging campaigns: a monochrome map at 250 m/pixel and an eight-color, 1-km/pixel color map. Apart from small gaps, which will be filled in during the next solar day, these global maps now provide uniform lighting conditions ideal for assessing the form of Mercury’s surface features as well as the color and compositional variations across the planet. The orthographic views seen here, centered at 75° E longitude, are each mosaics of thousands of individual images. At right, images taken through the wide-angle camera filters at 1000, 750, and 430 nm wavelength are displayed in red, green, and blue, respectively.

Release Date: October 5, 2011

Image Credit: NASA/Johns Hopkins

 

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Image Gallery

(1) The Interior of Kuiper: The rayed crater Kuiper (11.3° S, 328.6° E), as seen by MESSENGER’s wide-angle camera. The smooth regions on Kuiper’s floor and to its south consist of rock that was melted by the impact that created the crater. This impact melt ponded and solidified as smooth plains. Kuiper is 62 km in diameter and is an important stratigraphic marker in Mercury’s geologic history.

(2) Revisiting Rachmaninoff: This image, taken with the Wide Angle Camera (WAC), shows Rachmaninoff, a double-ring basin named in March 2010 for the Russian composer, pianist and conductor Sergei Rachmaninoff (1873-1943). Rachmaninoff was first imaged in its entirety during MESSENGER's third Mercury flyby. Of particular interest to geologists are the troughs, or "graben", on the basin floor, which are thought to have formed as the central smooth, volcanic plains cooled or possibly as other tectonic forces pulled the crust apart.

(3) Crater Close-Up: This image, taken with the Narrow Angle Camera (NAC), gives us a close-up view of an unnamed complex crater. First imaged at high resolution by MESSENGER in July 2011, this crater displays central peaks and terraced walls. The terraces, or "slumps", are generally caused by material collapsing down the steep walls of the crater. Due to the detail still visible in the ejecta blanket and its comparatively high reflectance, this crater is thought to be relatively young.

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

 

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Enwonwu, Grieg & Bronte

(1) The beautiful rayed crater at the left edge of the image is named for Benedict Enwonwu, a Nigerian sculptor and painter who lived from 1921-1994. Enwonwu crater is about 38 km in diameter. Its bright rays extend for hundreds of kilometers from the rim of the crater.

(2) The large impact crater at the right top edge of the image is Grieg (59 km diameter). The eponym is Edvard Grieg (1843-1907), a Norwegian composer. The crater has a small remnant central peak. The formation of a smaller crater has destroyed part of Grieg's western rim.

(3) This image contains four large impact craters of about the same size. Bronte, thought to be the oldest, is near the center of the right edge of the image and is about 68 km in diameter. The younger crater, Degas, with its sharp rim, formed just tangent to Bronte. Bronte is named for sisters and English novelists Charlotte (1816-1855), Emily (1818-1848), and Anne (1820-1849) and their brother Branwell (1817-1848) who was an author and painter.

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

 

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Image Galery

Nördliche und südliche Polargebiete:

(1) This image extends from about 86 to 88 degrees North. Most of the area is in darkness since the Sun is barely above the horizon at this high latitude. The impact crater at the lower left casts a long shadow across the silent, dimly lit landscape. The crater's eastern rim just catches the Sun, forming an illuminated arc.

(2) The south pole of Mercury, indicated here by an X, lies within the crater Chao Meng-Fu (named for a 13th century Chinese painter and calligrapher). Much of the interior of this crater lies in permanent darkness, and it is known to host radar bright features.

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

 

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Image Gallery

Dominici and Homer - in Color: Dominici crater, the very bright crater to the top of this image, exhibits bright rays and contains hollows. This crater lies upon the peak ring of Homer Basin, a very degraded peak ring basin that has been filled by volcanism. This image contains several examples of craters that have excavated materials from depth that are spectrally distinct from the surface volcanic layers, providing windows into the subsurface. MESSENGER scientists are estimating the approximate depths of these spectrally distinct materials by applying knowledge of how impacts excavate material during the cratering process. The 1000, 750, and 430 nm bands of the Wide Angle Camera are displayed in red, green, and blue, respectively.

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

 

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22.000 Bilder und 99,9% der Oberfläche von Merkur

The image shows a global mosaic that covers over 99.9% of Mercury's surface! This mosaic is made primarily of MDIS images acquired as part of the surface morphology base map, which during the first six months of MESSENGER's orbital mission mapped over 98.7% of the surface with nearly 22,000 images. Variations in the morphological appearance of the surface are due to differences in the Sun illumination conditions and viewing geometries for the different images taken over those six months. In this mosaic, small gaps in the surface morphology base map have been filled by images taken as part of the color base map imaging campaign. A few remaining gaps have been filled by data obtained by a combination of Mariner 10 and MESSENGER flybys, most of which is visible near the north pole.

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

 

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Image Gallery

(1) Eastern edge of Caloris basin

(2) Pourquoi Pas Rupes

(3) Center of Caloris Basin

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

 

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Re: Messenger Update

Noch ein Nachtrag zum Orbit Status von Messenger:

Fourth Orbit Adjustment Stretches MESSENGER's Orbit around Mercury

MESSENGER Mission News - October 24, 2011

The MESSENGER spacecraft successfully completed its fourth orbit-correction maneuver today to increase the period of the spacecraft's orbit around the innermost planet from 11 hours 46 minutes to a precise 12 hours.

MESSENGER was 198 million kilometers (123 million miles) from Earth when the 159-second maneuver began at 6:12 p.m. EDT. Mission controllers at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., verified the start of the maneuver about 11 minutes, 1 second later, when the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network tracking station outside Goldstone, Calif.

This is the fourth of five maneuvers planned for the primary orbital phase of the mission to keep orbital parameters within desired ranges for optimal scientific observations. MESSENGER's orbital velocity was changed by a total of 4.2 meters per second (9.4 miles per hour) to make the corrections essential for continuing the planned measurement campaigns.

Most of the instruments were placed in a passive state during the burn, but the instruments were reconfigured at 7:05 p.m. EDT to resume scientific observations of the planet.

MESSENGER Mission Systems Engineer Eric Finnegan, of APL, said the engine burn was executed as planned. "The team was well-prepared for the maneuver, and MESSENGER is right where it needs to be to continue revealing new details about Mercury," he said.

The next orbit-correction maneuver is scheduled for December 5.

Image Gallery

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

 

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Re: Messenger Update

Heiße Pole auf Merkur: Das grüne Quadrat liegt auf dem Äquator von Merkur und markiert den Längengrad 180°. Zusammen mit dem diametral gegenüberliegenden Punkt beim Längengrad 0° bildet er einen von zwei "hot poles" (Hitzepole). An diesen geographischen Punkten ist die Sonneneinstrahlung am intensivsten, nämlich etwa 2.5 mal so stark wie an den Äquatorpunkten bei Länge 90° und 270°. Die Ursache für diese ungleichmäßige Sonneneinstrahlung ist die stark elliptische Bahn und die Kopplung von Eigenrotation und Bahnumlauf (Spin/Bahn-Kopplung). Diese "Hot Spots" zeigen abwechselnd zur Sonne, wenn der Planet im Perihel seiner elliptischen Bahn steht:

Wikipedia

This varying distance to the Sun, combined with a 3:2 spin-orbit resonance of the planet’s rotation around its axis, result in complex variations of the surface temperature. This resonance makes a single day on Mercury last exactly two Mercury years, or about 176 Earth days.

Anders als bei der Erde hat Merkur keine nennenswerte Bahnneigung und entsprechende Jahreszeiten. Diese Spin-Orbit Kopplung erzeugt jedoch eine ganz andere orts- und zeitabhängige Variation der Sonneneinstrahlung.

Messenger Image Gallery

Cruel Summer: The small green square in this image marks the point at zero degrees latitude and 180° longitude on Mercury's surface. This is one of Mercury's two "hot poles." The other is at 0° latitude and 0° longitude. Mercury's eccentric orbit and spin-orbit coupling combine so that one or the other of these "hot poles" points toward the Sun when Mercury passes closest to the Sun in its orbit, and the Sun is overhead longer at these points than anywhere else on the planet. Therefore the "hot poles" receive about two and one-half times more solar radiation than the 90° and 270° longitudes and hence get much hotter. Since Mercury's rotation axis has essentially no tilt relative to its orbital plane (unlike the Earth, which has a tilt of 23°), Mercury does not have true seasons. But depending on the location, portions of the surface experience hotter "summers".

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

 

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NASA extends Messenger mission

NASA has announced that it will extend the MESSENGER mission for an additional year of orbital operations at Mercury beyond the planned end of the primary mission on March 17, 2012. The MESSENGER probe became the first spacecraft to orbit the innermost planet on March 18, 2011.

 

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Mercury Globe 0°N, 90°E (klick on image to show full size)

(1) The above image shows an orthographic projection of this global mosaic centered at 0°N, 90°E. The peak-ring basin Rachmaninoff can be seen in the northwest portion of the globe, Rembrandt basin can be seen towards the south, and Eminescu and Raditladi can be seen just east of center. The edge of the Caloris basin is just visible along the eastern edge of this globe.

Release Date: November 30, 2011

Mercury Globe 0°N, 0°E (klick on image to show full size)

(2) The above image shows an orthographic projection of this global mosaic centered at 0°N, 0°E. The rayed crater Debussy can be seen towards the bottom of the globe and the peak-ring basin Rachmaninoff can be seen towards the eastern edge.

Release Date: November 29, 2011

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

 

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Mercury Globe 0°N, 180°E (klick on image to show full size)

The above image shows an orthographic projection of this global mosaic centered at 0°N, 180°E. Caloris basin is prominently featured in this view, dominating the northern hemisphere. Just south of Caloris lies the 225-km-diameter basin, Mozart. Towards the center of the globe, Tolstoj is visible with an annulus of low-reflectance material. Beethoven basin is just visible along the eastern edge of the globe.

Release Date: December 1, 2011

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

 

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'Sleepy' Hollows on Mercury

Inspiriert von Sleepy Hollow, einer Legende von Washington Irving und dem gleichnamigen Film von Tim Burton,
aber auf einer weit entfernten Welt:

NASA on YouTube: The Sleepy Hollows on Mercury

NASA Science: Strange Hollows

National Geographic

Image Captions:

(1) Hollows on the Hills: The central peaks of Eminescu are revealed here at high resolution, showing off an impressive collection of hollows. Some of these hollows have coalesced into larger formations. North is down in this image.

(2) The Pit of Scarlatti Scarlatti is a peak-ring basin with a diameter of 132 kilometers. Just north of the inner peak ring on the basin's floor is a large oblong pit, shown here in the highest resolution ever obtained. The large pit may have formed as a volcanic collapse feature, and this high-resolution view shows many hollows located on the pit's wall. Members of the MESSENGER team are using images like this one to unravel the geologic relationship between Scarlatti's pit and these newly seen hollows.

(3) Blanket of Hollows: This high-resolution NAC image shows a fresh, simple crater. Simple craters are numerous on Mercury's surface, but this one is remarkable because of the many hollows visible in the crater's ejecta blanket. Stunning examples of hollows have been seen on the floors of the larger craters of Raditladi, Eminescu, Tyagaraja, Sander, and Kertesz.

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

 

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(1) Spokes & Troughs: The troughs of Pantheon Fossae extend across this scene, located between Cunningham and Apollodorus craters. This 14-km crater appears to have formed after Pantheon Fossae, with its ejecta covering the troughs. - Date acquired: December 25, 2011

(2) Smooth Plains? Mercury's north polar region contains an expansive area of volcanic smooth plains. The stark image shown here is actually located in that "smooth" plains region! At this high northern latitude, the Sun is always low on the horizon, resulting in high incidence angles and long shadows that accentuate the topography and texture of the surface. - Date acquired: January 13, 2012

(3) Two views of the crater Berkel. The image on the [top] is a monochrome image obtained when the Sun was lower on the horizon than when the color image on the [bottom] was collected. As a result, the [top] image emphasizes the topography of the surface (due to the presence of shadowing), whereas the image on the [bottom] is dominated by inherent differences in reflectance and color. The impact that formed Berkel excavated dark subsurface material and deposited it around the crater's rim. The presence of this low reflectance material causes the floor of the crater to appear black in the color image. - Date acquired: January 23, 2012

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

 

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Messenger Image Gallery

(1) From Terminator to Limb

(2) Color Close-Up of Kuiper

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

 

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Messenger Image Gallery

(1) Shakespeare

(2) Interior of Rembrandt

(3) Amaral

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

 

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Messenger Image Gallery

(1) 14 km Durchmesser (noch ohne Namen)

(2) Bronte (oben rechts) und Degas (bläulich) in Sobkou Planitia

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

 

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Messenger Image Gallery

(1) The high-reflectance and hollow-filled floor of de Graft crater is visible at center left, and a similar high-reflectance smaller crater is located to the northeast. Streaking across the scene from north to south are rays from Hokusai crater, located over 1,500 km away.

(2) Sprinkles of Blue: Firdousi is a relatively fresh impact crater approximately 96 kilometers in diameter. Its abundant secondary craters dominate the surroundings, and many have haloes of high-reflectance, relatively blue ejecta.

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

 

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Messenger Image Gallery

(1) Chekhov & Schubert

(2) Hesiod

(3) No names yet

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

 

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Messenger Image Gallery

(1) Crater Sher-Gil - Uncovering a Dark Past

Impact craters serve as probes into a planet's subsurface, excavating and exposing material from depth that would be otherwise unobservable.

(2) Close-up of unnamed crater in northern hemisphere

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

 

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Messenger Image Gallery

(1) Scarped crater in Rembrandt basin

(2) Tectonic subduction scarp

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

 

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Messenger Image Gallery

Farbkodiertes Höhenprofil vom Beethoven Becken mit einem Höhenunterschied von 8000 m

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

 

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Messenger Mission News

Messenger Sonde jetzt seit einem Jahr im Orbit um Merkur und kein bisschen müde ...

Spiegel - 21. März 2012 - Sonde entdeckt riesige Eisenkugel im Merkur

Naja - dass Merkur einen riesigen Eisenkern hat, ist schon länger bekannt - siehe z.B. hier und da - neu ist allerdings, dass dieser Eisenkern noch größer ist als bislang bekannt war, nämlich mehr als die Hälfte seines Volumens.

Discovery News - March 21, 2012 - Mystery Rising Within Mercury

Messenger Mission News - March 21, 2012

MESSENGER completed its one-year primary mission on March 17. The latest findings are presented in two papers published online in Science Express today, and in 57 papers presented this week at the 43rd Lunar and Planetary Science Conference in The Woodlands, Texas.

Maria T. Zuber et al. - Topography of the Northern Hemisphere of Mercury from MESSENGER Laser Altimetry

Laser altimetry by the MESSENGER spacecraft has yielded a topographic model of the northern hemisphere of Mercury. The dynamic range of elevations is considerably smaller than those of Mars or the Moon. The most prominent feature is an extensive lowland at high northern latitudes that hosts the volcanic northern plains. Within this lowland is a broad topographic rise that experienced uplift after plains emplacement. The interior of the 1500-km-diameter Caloris impact basin has been modified so that part of the basin floor now stands higher than the rim. The elevated portion of the floor of Caloris appears to be part of a quasi-linear rise that extends for approximately half the planetary circumference at mid-latitudes. Collectively, these features imply that long-wavelength changes to Mercury’s topography occurred after the earliest phases of the planet’s geological history.

David E. Smith et al. - Gravity Field and Internal Structure of Mercury from MESSENGER

Radio tracking of the MESSENGER spacecraft has provided a model of Mercury’s gravity field. In the northern hemisphere, several large gravity anomalies, including candidate mass concentrations (mascons), exceed 100 mGal. Mercury’s northern hemisphere crust is thicker at low latitudes and thinner in the polar region and shows evidence for thinning beneath some impact basins. The low-degree gravity field, combined with planetary spin parameters, yields the moment of inertia C/MR² = 0.353 ± 0.017, where M and R are Mercury’s mass and radius, and a ratio of the moment of inertia of Mercury’s solid outer shell to that of the planet of Cm/C = 0.452 ± 0.035. A model for Mercury’s radial density distribution consistent with these results includes a solid silicate crust and mantle overlying a solid Fe-S layer and an Fe-rich liquid outer core and perhaps a solid inner core.

 

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Re: Messenger Update

MESSENGER Modifies Orbit to Prepare for Extended Mission

Nach einem Jahr in einem stark elliptischen Orbit soll dieser Mitte April durch eine weitere Bahnkorrektur etwas "runder" gemacht werden. Die Umlaufzeit soll sich dann von gegenwärtig 12 h auf 8 h verkürzt werden. Damit verbringt die Sonde dann einen größeren Anteil ihrer Umlaufzeit in der Nähe des Planeten. Der geringste Abstand zur Oberfläche soll bei ca. 200 km bleiben.

Where is Messenger?

(1) View from the Earth - This image shows MESSENGER's location in its current orbit as seen from the direction of the Earth.

(2) View from the Sun - This image shows MESSENGER's location in its current orbit as seen from the direction of the Sun.

(3) Full View of Spacecraft Orbit - This image shows MESSENGER's location in its current orbit as seen from a viewpoint that provides visibility of 100% of the orbit at all times.

Credit: NASA and Johns Hopkins University Applied Physics Laboratory

 

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Messenger Update

Wie bereits angekündigt, befindet sich Messenger nach zwei weiteren Bahnkorrekturen nun in einem weniger langgestreckten Orbit mit einer kürzeren Umlaufperiode von nur noch 8 Stunden.

April 16, 2012 - MESSENGER Adjusts Orbit for a Closer Look at Mercury
The MESSENGER mission successfully completed the first of two maneuvers designed to reduce the spacecraft's orbital period about Mercury. This new trajectory will pave the way for more detailed measurements and targeted observations of the Sun's closest neighbor. The spacecraft was 124 million kilometers from Earth when the 188-second maneuver began at 3:13 p.m. EDT. This maneuver -- which adjusted the orbital period from 11 hours, 36 minutes to 9 hours, 5 minutes -- was designed to deplete the remaining oxidizer of the spacecraft's propulsion system in a final firing of the large bi-propellant thruster. A second maneuver, scheduled for the evening of April 20, will use the spacecraft's monopropellant system to complete the transition to an 8-hour orbit. After Friday's maneuver, the 8-hour orbit will remain highly eccentric, with MESSENGER travelling between 278 kilometers (172 miles) and 10,314 kilometers (6,409 miles) above Mercury's surface. Reducing the orbital period will increase from two to three the number of revolutions the spacecraft will make about the planet each day, increasing the time that the spacecraft will spend closer to the surface.

April 20, 2012 - MESSENGER Settles into Eight-Hour Orbit Around Mercury
MESSENGER mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., conducted the second of two maneuvers required to reduce the spacecraft's orbital period about Mercury. The first maneuver, completed on Monday, shortened the orbital period from 11.6 to 9.1 hours and consumed the remaining oxidizer, one of two propellants that fuel the higher-efficiency large thruster. With today's maneuver, accomplished with the spacecraft's four medium-sized thrusters, MESSENGER is now in the 8-hour orbit from which it will operate for the next year. MESSENGER was 133 million kilometers from Earth when the 4-minute maneuver began at 7:05 p.m. EDT. Mission controllers at APL verified the start of the maneuver 7 minutes and 23 seconds later, after the first signals indicating spacecraft thruster activity reached NASA's Deep Space Network tracking station in Canberra, Australia. The shorter orbit will allow MESSENGER's science team to address new questions about Mercury's composition, geological evolution, and environment that were raised by discoveries made during the first year of orbital operations.

Where is Messenger?

(1) View from the Earth: This image shows MESSENGER's location in its current orbit as seen from the direction of the Earth. Positions of stars with magnitude 5 or brighter are shown.

(2) View from the Sun: This image shows MESSENGER's location in its current orbit as seen from the direction of the Sun.

(3) Full View of Spacecraft Orbit; This image shows MESSENGER's location in its current orbit as seen from a viewpoint that provides visibility of 100% of the orbit at all times.

Credit: NASA and Johns Hopkins University Applied Physics Laboratory

 

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