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MESSENGER Planetary Conference Multimedia Page

Presenter #1
Brian J. Anderson, MESSENGER Deputy Project Scientist
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD

Image 1.1
image 1.1

Mercury’s magnetic field is distorted by the solar wind, which compresses the magnetic field on the dayside and stretches it out to form a long tail on the nightside. Interaction between the solar wind and the planetary field creates the bow shock and magntopause boundaries, as well as features noted in the figure. Two representative MESSENGER orbits are shown in green. When the spacecraft is closest to the planet at night the orbit takes the form of the solid green ellipse. One-half Mercury year later, the spacecraft is closest to the planet during the daytime and the orbit takes the form of the dashed green ellipse. The MESSENGER orbit carries the spacecraft across the magnetospheric boundaries and through each region of Mercury’s magnetic field. The challenge for MESSENGER scientists is to extract telltale signatures that indicate how Mercury’s magnetic field would look without the solar wind.

Credit: Courtesy of Science/AAAS.

Click on image to enlarge.



Image 1.2
image 1.2

One of the most basic questions about Mercury’s magnetic field is whether it is centered on the planet. For Mercury, one can locate the magnetic equator by noting where the magnetic field is parallel to the spin axis of the planet. The Bρ component is the part of the magnetic field pointing toward or away from the spin axis. (The Greek letter ρ is used to label this direction.) The point where Bρ = 0 identifies the magnetic equator crossing.

Credit: Courtesy of Science/AAAS.

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Image 1.3
image 1.3

Spacecraft position and magnetic field measurements for one pass of MESSENGER through Mercury’s magnetosphere. The top panel shows the distance of the MESSENGER spacecraft from the center of Mercury in black and the latitude of the spacecraft in red. The bottom panel shows the sunward (X), duskward (Y), and northward (Z) components of the magnetic field together with the total (Total) and negative of the total (-Total). The inbound and outbound bow shocks are evident in the sharp steps in the total field near the left and right ends of the lower plot. The total field reaches about 500 nT (nano-Tesla) near the closest approach to the planet. The equator crossing occurs near 02:30 UTC in the shaded time period. Note that the X and Y magnetic field components pass through zero slightly before the spacecraft crosses the geographic equator (latitude equal to zero).

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

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Image 1.4
image 1.4

A close-up of the shaded time period in the previous figure. Here, the magnetic field is shown in its ρ, φ and z components. Bφis positive toward the east and is very small. The crossing of the geographic occurs nearly two and a half minutes after the point where Bρ = 0, indicating that the MESSENGER spacecraft crossed the magnetic equator when the spacecraft was still north of the geographic equator.

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

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Image 1.5
image 1.5

The north-south position (Zρ0) of the magnetic equator determined from over 370 orbits of MESSENGER about Mecury. The points cluster between 400 and 600 km northward of the geographic equator with an average of 480 km. The points are colored red if the magnetic field in the solar wind (interplanetary magnetic field or IMF) was pointed toward Mercury from the Sun (IMF BX-MSO negative) and blue if the solar wind magnetic field pointed toward the Sun from Mercury (IMF BX-MSO positive). The magnetic field in the solar wind had been thought to be important in controlling the magnetic equator, but the data show no systematic variation with the IMF BX-MSO. There does appear to be some consitent variation in the magnetic latitude with longitude, suggesting subtle structure in the magnetic field. The consitent northward shift in the field and these smaller features in longitude are important clues about how the magnetic field is generated deep inside the planet. The hard work of modeling the internal dynamics to decipher these clues is just getting underway.

Credit: Courtesy of Science/AAAS.

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Image 1.6
image 1.6

Representative Mercury magnetic field lines are shown in yellow. The shift of the magnetic equator to the north means that there is a strong asymmetry between the northern and southern polar magnetic fields. At Mercury’s surface, the north polar magnetic field is nearly four times stronger than it is at the south pole.

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

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Image 1.7
image 1.7

The different magnetic fields in the north and south implies that the south is more exposed than the north to charged particles, whether from the solar wind or from energetic electrons accelerated near Mercury. This may mean that the discoloration of the surface resulting from bomardment by charged particles is greater in the south.

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

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Presenter #2
William McClintock, MESSENGER Co-Investigator
University of Colorado, Laboratory for Atmospheric and Space Physics, Boulder, CO.

Image 2.1

A coronal mass ejection (CME) is an extreme example of the interaction of the space environment with Mercury’s surface. CMEs can occur several times a day during times of maximum activity in the 11-year solar cycle. They travel at speeds of up to 3000 km/s, and the larger ones impact Mercury with sufficient force that they completely disrupt the magnetic field structure and allow solar wind plasma to directly impact the dayside surface.

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

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Image 2.2


The panels on the left illustrate the three primary sources of exospheric material. Photon-stimulated desorption and evaporation result from incoming sunlight. Photon-stimulated desorption occurs when solar photons excite surface-bound atoms or molecules, causing them to be released to the exosphere. Sunlight also heats the surface, causing atoms and molecules to evaporate. These are both low-energy source processes, so released material reaches only low altitudes in the exosphere and usually returns to the surface. Ion sputtering occurs when ions in the solar wind impact the surface, “knocking off” atoms and molecules. Meteoroid vaporization occurs when incoming meteoroids, generally small dust particles, impact Mercury’s surface, causing the local surface material to vaporize and enter the exosphere. Both ion sputtering and meteoroid vaporization are high-energy source processes, and the released material can reach high altitude and be accelerated in the anti-sunward direction by radiation pressure to form a neutral tail. Eventually atoms in the tail become ionized and escape along open magnetic field lines.

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

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Image 2.3


The panel on the left illustrates the technique used by MESSENGER to observe the dayside exosphere. As the spacecraft travels along its trajectory (red arc in the figure), the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) views the exosphere along lines of sight perpendicular to the orbit. When the spacecraft crosses Mercury’s equatorial plane it executes a 180° roll, pointing MASCS into the sunlit exosphere. Lines of sight are color coded by the intensity of light emitted by exospheric constituents. They extend to infinity, but here they have been terminated close to the planet for clarity. This is an example of emission by neutral sodium, and the intensity (the number of atoms observed) increases rapidly as the line of sight approaches the surface. In contrast, intensities of calcium and magnesium, the other major exosphere species observed by MASCS, increase more slowly. The right panel shows plots of intensity as a function of altitude for three major species in the exosphere. The steepness of the lines tells us about the energies of the various processes that populate the exosphere. Sodium shows two temperatures, indicating that two different source processes are at work. Magnesium and calcium each exhibit a single temperature that is large compared with those for sodium.

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

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Image 2.4


The panel at lower right illustrates nightside exosphere (also termed tail) observations. As the spacecraft drifts south it rocks side-to-side in a fantail pattern, mapping out the locations of atoms in the tail. Intensities of the three major components show distinct distributions. Sodium is concentrated near the poles. This result is consistent with the idea that sodium atoms are lofted into the exosphere by solar wind plasma that impacts the dayside near the subsolar point. These atoms are then transported nightward by solar radiation pressure. The concentrations of calcium and magnesium observed in this region are too large to be explained by the processes that control sodium. In addition, calcium shows a dawn enhancement that is not observed in chemically similar magnesium.

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

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Presenter #3
Brett W. Denevi, Staff Scientist
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD

Image 3.1
image 3.1

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.

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

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Image 3.2

The X-Ray Spectrometer (XRS) on MESSENGER collects compositional information averaged over relatively large regions on Mercury’s surface, and signals diagnostic of the heavier elements are received only during times of high solar activity. The blue region outlined in this wide-angle camera (WAC) image mosaic shows the region visible to the XRS during a solar flare on 16 April 2011. The area is basaltic in composition. Basalts are common volcanic rocks on Earth and in lunar maria. This region is part of the vast, high-reflectance northern plains that cover approximately 6% of Mercury’s surface. The WAC filter bands at 1000, 750, and 430 nm wavelength are displayed in red, green, and blue, respectively.

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

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Image 3.3

The region of Mercury’s surface visible to the XRS during a solar flare on 16 June 2011. Near the center is the ~650-km-diameter Beethoven impact basin at 20° S, 235° E. This region has a higher Mg/Si ratio than the northern plains and is closer in composition to terrestrial komatiites, low-silica, high-temperature volcanic rocks that formed only very early in Earth’s history.

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

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Image 3.4

This image shows a map of smooth plains in the region visible to MESSENGER’s XRS during a solar flare on 16 June 2011. Mapped in green are plains of volcanic origin. These plains display flooding and embayment relationships and color contrasts typical of volcanic plains on Mercury. Yellow denotes plains of uncertain origin. Though they may also be volcanic, they lack definitive evidence for a volcanic origin and may have formed as fluidized impact ejecta, possibly from the Beethoven impact basin, or as impact melt. In blue are plains that formed when rock was melted by impacts. Even geologically complex regions, such as the area seen here, are often dominated by volcanic deposits, and their compositions are consistent with a volcanic origin.

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

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Image 3.5

The rayed crater Kuiper, 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. 

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

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Presenter #4
Noam R. Izenberg, Mercury Atmospheric and Surface Composition Spectrometer Instrument Scientist
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD

Image 4.1a

Mercury as seen in color according to the Mercury Atmospheric and Surface Composition Spectrometer (MASCS). This image takes individual MASCS observations from the first Mercury solar day in orbit at three wavelengths from the ultraviolet to the near-infrared and maps them over a mosaic of images obtained with MESSENGER’s Mercury Dual Imaging System (MDIS). In this color composite, 350 nm wavelength is used for blue, 575 nm for green, and 750 nm for red.

Image 4.1b

Just under half of the more than one million MASCS spectra gathered as of the halfway mark of the primary mission show brightness contrasts well correlated with MDIS color and geological structure. Letters denote geologic features on the surface: T = Tolstoj basin; P = Praxiteles crater; K = Kuiper crater, D = Debussy crater, H = Hokusai crater; R = Rachmaninoff basin; Rb = Rembrandt basin; C = Caloris basin.

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

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Image 4.2a

Spectral variation mapped by MASCS is strongest in the ultraviolet. Whereas simple color representations allow identification of brightness features, there is not a great deal of color contrast on Mercury at visible to near-infrared wavelengths. In contrast, there is greater variability at ultraviolet wavelengths. In this color composite, red is 575 nm reflectance, green is the spectral slope (i.e., a measure of the increase in reflectance with increasing wavelength) from the visible to the near-infrared, and blue is a ratio of spectral slopes (the ultraviolet/visible slope over the visible/near-infrared slope). This combination, notably the blue-purple-pink ranges, indicates areas where the ultraviolet variations correlate with geological features.

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

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Image 4.2b

The interior of Praxiteles as well as Kuiper, Debussy, and Rachmaninoff are distinct from their surroundings in this rendering.  The interiors of Rembrandt and Caloris basins also differ from their surroundings at ultraviolet wavelengths. The Tolstoj basin, in contrast, is seen largely as a brightness feature, with little to distinguish it spectrally from its surroundings.

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

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Image 4.3

Mercury’s northern plains appear distinctive at ultraviolet wavelengths. The viewing geometry in the far north is extreme, with high incidence angles, but the magenta colors in this MASCS rendering conform reasonably well with the locations of plains material inferred from MDIS images. The color of the plains in this figure, indicating higher spectral slope ratio and overall brightness than in surrounding areas, is also shared by the interior of the Caloris basin, hinting at similar materials in these two regions.

Credit: Courtesy of Science/AAAS.

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Image 4.4

Variation in surface reflectance at ultraviolet wavelengths provides clues to mineralogy. Here we see two craters with very different interiors. The images are color MDIS composites that bring out contrasts at visible and near-infrared wavelengths. The crater Moody (left) has a reddish center. High-resolution images of similar terrain elsewhere on Mercury have led to the hypothesis that these materials are pyroclastic in origin. Below the MDIS image is a comparison of the average spectral reflectance of Mercury (in black) with that for an area (red spot) in the interior of Moody (in green).  Kuiper (right) is a comparatively young impact crater with distinctive rays and a bright floor. A MASCS spectrum of an area (red spot) in the interior of this crater (bottom right in green, compared again with average Mercury in black) shows a marked difference from that for the interior of Moody and a steep drop-off into the ultraviolet. This type of spectrum is seen elsewhere on Mercury in association with young impact craters and other features.

Variations in ultraviolet reflectance may be caused in part by oxygen-metal charge transfer (OMCT) bands. The variations seen are consistent with a contribution from OMCT bands associated with iron, as long as the overall iron abundance is low, an inference consistent with the lack of an absorption band in the near-infrared seen by MASCS and with the low but measurable iron abundance indicated by MESSENGER’s X-Ray Spectrometer.

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

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