terça-feira, 5 de fevereiro de 2008

MESSENGER at Mercury

For the first time in more than 30 years, a spacecraft will return to Mercury, providing images from sections of the planet that have never been viewed by a spacecraft.
Provided by the Johns Hopkins University
This visible-infrared image shows an incoming view of Mercury, about 80 minutes before MESSENGER's closest pass of the planet on January 14, 2008, from a distance of about 27,000 kilometers (17,000 miles). NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [View Larger Image]
Updated January 22, 2008
One week ago, the MESSENGER spacecraft transmitted to Earth the first high-resolution image of Mercury by a spacecraft in over 30 years, since the three 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 nanometers (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 image released last week.

Image sequences acquired through the 11 different MDIS filters are being used to distinguish subtle color variations indicative of different rock types. By analyzing color differences across all 11 filters, the MESSENGER team is investigating the variety of mineral and rock types present on Mercury's surface. Such information will be key to addressing fundamental questions about how Mercury formed and evolved.

Mercury has a diameter of about 3030 miles (4880 kilometers), and the smallest feature visible in this color image is about 6 miles (10 kilometers) in size.
This image was acquired about 98 minutes after MESSENGER's closest approach to Mercury, when the spacecraft was at a distance of about 21,000 miles (33,000 kilometers). NASA/JHUAPL/CWI [View Larger Image]
Updated January 21, 2008
One week ago, on January 14, 2008, MESSENGER passed 124 miles (200 kilometers) above the surface of Mercury and snapped the first pictures of a side of Mercury not previously seen by a spacecraft. The image to the right shows that previously unseen side, with a view looking toward Mercury's south pole. The southern limb of the planet can be seen in the bottom right of the image. The bottom left of the image shows the transition from the sunlit, day side of Mercury to the dark, night side of the planet, a transition line known as the terminator. In the region near the terminator, the sun shines on the surface at a low angle, causing the rims of craters and other elevated surface features to cast long shadows, accentuating height differences in the image.

This image is just one in a planned sequence of 42 images acquired by the Narrow Angle Camera of the Mercury Dual Imaging System (MDIS). From these 42 images, the MESSENGER team is creating a high-resolution mosaic image of this previously unseen portion of Mercury. During the flyby, MDIS took more than 1,200 images, which are being combined to create multiple mosaics with different resolutions and of different portions of the planet. The creation of high-resolution mosaic images will enable a global view of Mercury's surface and will be used to understand the geologic processes that made Mercury the planet we see today.
This picture provides a global context for the MDIS Narrow Angle Camera (NAC) images taken while MESSENGER was inbound. This image was taken about 80 minutes before closest approach from a distance of about 17,000 miles (27,000 kilometers) and shows features as small as 6 miles (10 kilometers). NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [View Larger Image]
Updated January 18, 2008
As MESSENGER neared Mercury on January 14, 2008, the spacecraft's Wide Angle Camera on the Mercury Dual Imaging System (MDIS) took images of the planet through each of its 11 filters. This image of the planet's full crescent was taken using the 7th filter, in light near the far-red end of the visible spectrum (750 nm). The image shows portions of Mercury previously seen by Mariner 10, but when Mariner 10 flew by the planet at each of its encounters the Sun was nearly overhead. For this MESSENGER flyby, in contrast, the Sun is shining obliquely on regions near the day/night boundary (called the terminator) on the right-hand side of the crescent, revealing the surface topography in sharp relief. This image illustrates how MESSENGER, during its future flybys and subsequent orbital mission, will teach us much about the portion of Mercury already imaged by Mariner 10, and not just because of its superior camera and close proximity to the planet. The solar lighting geometry makes an enormous difference.

A day after its successful flyby of Mercury, the MESSENGER spacecraft turned toward Earth on Tuesday and began downloading the 500 megabytes of data that had been stored on the solid-state recorder during the encounter. All of those data, including 1,213 images from the Mercury Dual Imaging System (MDIS) cameras, have now been received by the Science Operations Center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. Preliminary analysis of these data by the MESSENGER Science Team has confirmed that all seven MESSENGER instruments are healthy and operated as planned during the flyby.

As MESSENGER flew by the planet, it missed its targeted aim point by only 5.12 miles (8.25 kilometers), affording the critical gravity assist needed to continue on a course to become, in 2011, the first spacecraft ever to orbit Mercury. During this first encounter, the payload successfully conducted a carefully orchestrated sequence of observations designed to take full advantage of the geometry of the flyby trajectory and to optimize the science return from each instrument.

In addition to images of the previously unseen portion of the planet's surface, measurements were made that will contribute to the characterization of all aspects of Mercury and its environment, from its metallic core to the far reaches of its magnetosphere. "We have one excited science team," says MESSENGER Project Manager, Peter D. Bedini, of APL, "and their enthusiasm is contagious."

The analysis of these data is just beginning, but there are already indications that new discoveries are at hand.
The image shows a variety of surface textures, including smooth plains at the center of the image, many impact craters (some with central peaks), and rough material that appears to have been ejected from the large crater to the lower right. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [View Larger Image]
Updated January 17, 2008
As the MESSENGER spacecraft drew closer to Mercury for its historic first flyby, the spacecraft's Narrow Angle Camera (NAC) on the Mercury Dual Imaging System (MDIS) acquired an image mosaic of the sunlit portion of the planet. This image is one of those mosaic frames and was acquired on January 14, 2008, when the spacecraft was about 11,000 miles (18,000 kilometers) from the surface of Mercury, about 55 minutes before MESSENGER's closest approach to the planet.

This large 120 miles (about 200 milometers) crater was seen in less detail by Mariner 10 more than 3 decades ago and was named Sholem Aleichem for the Yiddish writer. In this MESSENGER image, it can be seen that the plains deposits filling the crater's interior have been deformed by linear ridges. The shadowed area on the right of the image is the day-night boundary, known as the terminator. Altogether, MESSENGER acquired over 1200 images of Mercury, which the science team members are now examining in detail to learn about the history and evolution of the innermost planet.
This MESSENGER image was taken from a distance of about 11,000 miles (18,000 kilometers), about 56 minutes before the spacecraft's closest encounter with Mercury. It shows a region roughly 300 miles (500 km) across, and craters as small as 0.6 mile (1 km) can be seen in the image above. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [View Larger Image]
Updated January 16, 2008
As MESSENGER approached Mercury on January 14, 2008, the spacecraft's Narrow-Angle Camera on the Mercury Dual Imaging System (MDIS) instrument captured this view of the planet's rugged, cratered landscape illuminated obliquely by the Sun. The large, shadow-filled, double ringed crater to the upper right was glimpsed by Mariner 10 more than three decades ago and named Vivaldi, after the Italian composer. Its outer ring has a diameter of about about 125 miles (200 kilometers). MESSENGER's modern camera has revealed detail that was not well seen by Mariner 10, including the broad ancient depression overlapped by the lower-left part of the Vivaldi crater. The MESSENGER science team is in the process of evaluating later images snapped from even closer range showing features on the side of Mercury never seen by Mariner 10. It is already clear that MESSENGER's superior camera will tell us much that could not be resolved even on the side of Mercury viewed by Mariner's vidicon camera in the mid-1970s.
The MESSENGER spacecraft snapped this image yesterday morning from a distance of 470,000 miles (760,000 km). The image has a resolution of about 12 miles (20 km) per pixel. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [View Larger Image]
Updated January 14, 2008
NASA's MESSENGER spacecraft is on track for its first flyby of Mercury today. The craft will explore the planet from as close as 125 miles (200 kilometers).

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) craft, launched August 3, 2004, will be the first spacecraft to study the innermost planet while in orbit around it. Following three flybys during the next 3 years, MESSENGER will reach orbit around Mercury in 2011.

Planetary scientists are eager to get a closer look at the Sun's nearest neighbor.

"We are about to visit Mercury for the first time in more than 30 years, and we can't wait," says MESSENGER principal investigator Sean Solomon of the Carnegie Institution of Washington.

NASA's Mariner 10 is the only other spacecraft to visit the planet closest to the Sun.

"We'll be making close-in observations of the composition of Mercury's surface and atmosphere, and we'll be probing deeper into the planet's magnetosphere than we've ever been," says Solomon.

The MESSENGER probe's Mercury Dual Imaging System cameras began snapping pictures of the planet January 9. NASA plans a mission update on the Mercury flyby January 30.

Visit MESSENGER's online newsroom.
January 8, 2008
On January 9, MESSENGER's Mercury Dual Imaging System cameras began gathering pictures of Mercury as the probe zeros in on the planet.

"With just one week to go before the flyby, the spacecraft is on target to encounter the planet at an altitude of 202 kilometers," says Mission Systems Engineer Eric Finnegan of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. "All subsystems and instruments are operating nominally and configured for the start of the flyby sequence, except for the Mercury Laser Altimeter and part of the Gamma-Ray Spectrometer, which we'll turn on just before the flyby."

Over the next week, the team will make final flyby preparations and upload the final command sequences for the encounter.

"We are about to visit Mercury for the first time in more than 30 years, and we can't wait," says MESSENGER Principal Investigator Sean Solomon of the Carnegie Institution of Washington. "In addition to providing the critical gravity assist that will move MESSENGER along its path toward Mercury orbit insertion in March 2011, this flyby will let us see parts of Mercury never before viewed by spacecraft. We'll be making close-in observations of the composition of Mercury's surface and atmosphere, and we'll be probing deeper into the planet's magnetosphere than we've ever been. We expect many surprises."

On December 19th, MESSENGER's 19th trajectory correction maneuver (TCM-19) changed the spacecraft's velocity by 3.6 feet per second (1.1 meters per second), directing MESSENGER closer to its intended target for the first flyby. TCM-19 went so well that the mission design and navigation teams have decided that a TCM scheduled for January 10 will not be needed.

"Cancellation of this maneuver is a demonstration of the near-perfect execution of TCM-19 just prior to the start of the holiday season," says Finnegan.
Experience MESSENGER's Mercury flyby virtually
Artist rendition of MESSENGER
Planetary scientists have sent the MESSENGER space probe to Mercury to answer questions left hanging after the visit of the last spacecraft, Mariner 10, in the mid-1970s. NASA / JHUAPL / CIW [View Larger Image]

See Mercury through the "eyes" of MESSENGER's imagers with the Mercury Flyby Visualization Tool. This new web feature offers a unique opportunity to see simulated views of Mercury from MESSENGER's perspective during approach, flyby, and departure, or in real-time (as the observations actually occur).

This tool combines the best available image map of Mercury's surface with observation sequences for the Mercury Dual Imaging System (MDIS), Mercury Atmospheric and Surface Composition Spectrometer (MASCS), and Mercury Laser Altimeter (MLA). The map of Mercury's surface combines Earth-based low-resolution radar images from the Arecibo Observatory in Puerto Rico and image mosaics from the Mariner 10 spacecraft flybys of Mercury in 1974 and 1975.

Lucimary Vargas de Oliveira Guardamino Espinoza
Além Paraíba-MG-Brasil
Observatório Astronômico Monoceros
Estacão Meteorológica Nº083/5ºDISME-INMET
CEPESLE -Centro de Estudos e Pesquisas Sertões do Leste
AHAP-Arquivo Histórico de Além Paraíba
MSN: observatoriomonoceros@hotmail.com

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