Planet Mercury as seen from the MESSENGER spacecraft in 2008. Credit: NASA/JPL
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According to data from the The Fast Imaging Plasma Spectrometer (FIPS) onboard NASA’s MESSENGER spacecraft, the solar wind is “sandblasting” the surface of Mercury at its polar regions.
Based on findings from one of seven different papers from the MESSENGER mission to be published in the Sept. 30th edition of Science, sodium and oxygen particles are charged in a manner similar to Earth’s own Aurora Borealis.
How are the University of Michigan researchers able to detect and study this phenomenon?
Using the FISP, the scientists at the University of Michigan have taken measurements of Mercury’s exosphere and magnetosphere. The data collected has provided researchers with a better understanding of interactions between Mercury and our Sun. FIPS data has also confirmed theories regarding the composition and source of particles in Mercury’s space environment.
“We had previously observed neutral sodium from ground observations, but up close we’ve discovered that charged sodium particles are concentrated near Mercury’s polar regions where they are likely liberated by solar wind ion sputtering, effectively knocking sodium atoms off Mercury’s surface,” said FIPS project leader Thomas Zurbuchen (University of Michigan).
In a UM press release, Zurbuchen added, “We were able to observe the formation process of these ions, and it’s comparable to the manner by which auroras are generated in Earth’s atmosphere near polar regions.”
Given that Earth and Mercury are the only two magnetized planets in the inner solar system (Mars is believed to have had a magnetic field in its past), the solar wind is deflected around them. The solar wind has made recent news due to recent outbursts from the Sun causing visible aurorae, caused by the interaction of charged particles from the Sun and Earth’s relatively strong magnetosphere. While Mercury does have a magnetosphere, compared to Earth’s it is relatively weak. Given Mercury’s weak magnetosphere and close proximity to the Sun, the effects of the solar wind have a more profound effect.
The Fast Imaging Plasma Spectrometer on board MESSENGER has found that the solar wind is able to bear down on Mercury enough to blast particles from its surface into its wispy atmosphere. Image Credit: Shannon Kohlitz, Media Academica, LLC
“Our results tell us is that Mercury’s weak magnetosphere provides very little protection of the planet from the solar wind,” Zurbuchen said.
Jim Raines, FIPS operations engineer (University of Michigan) added, “We’re trying to understand how the sun, the grand-daddy of all that is life, interacts with the planets. It is Earth’s magnetosphere that keeps our atmosphere from being stripped away. And that makes it vital to the existence of life on our planet.”
A high-resolution monochrome image has been combined with a lower-resolution enhanced-color image. The hollows appear in cyan, a result of their high reflectance and bluish color relative to other parts of the planet. The large pit in the center of the crater may be a volcanic vent, from which the orange material erupted. Credit: Courtesy of Science/AAAS
The MESSENGER team also released other results from the mission, including new evidence that flood volcanism has been widespread on Mercury, the first close-up views of Mercury’s “hollows,” and the first direct measurements of the chemical composition of Mercury’s surface.
MESSENGER, as well the the Mariner 10 flyby mission saw unusual features on the floors and central mountain peaks of some impact craters which were very bright and have a blue color relative to other areas of Mercury. This type of feature is not seen on the Moon, and were nicknamed “hollows.”
Now, with the latest MESSENGER data, hollows have been found over a wide range of latitudes and longitudes, suggesting that they are fairly common across Mercury. Many of the depressions have bright interiors and halos.
“To the surprise of the science team, it turns out that the bright areas are composed of small, shallow, irregularly shaped depressions that are often found in clusters,” says David Blewett, a staff scientist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and lead author of one of the Science reports. “The science team adopted the term ‘hollows’ for these features to distinguish them from other types of pits seen on Mercury.”
Blewett added the hollows detected so far have a fresh appearance and have not accumulated small impact craters, indicating that they are relatively young.
Spectacular view of the Degas crater from MESSENGER in Mercury orbit. This high-resolution view of Degas crater was obtained as a targeted observation (90 m/pixel). Impact melt coats its floor, and as the melt cooled and shrank, it formed the cracks observed across the crater. For context, Mariner 10’s view of Degas is shown at left. Degas is 52 km in diameter and is centered at 37.1° N, 232.8° E. Credit: NASA/The Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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NASA’s MESSENGER probe to Mercury, the scorched, innermost planet of our solar system, is sending back so much startling and revolutionary data and crystal clear images that the results are forcing scientists to toss out previously cherished theories and formulate new ones even as the results continues to pour in. And the mission has barely begun to explore Mercury’s inner secrets, exterior surface and atmospheric environment.
MESSENGER became the first spacecraft ever to orbit planet Mercury on March 18, 2011 and has just completed the first quarter of its planned one year long mission – that’s the equivalent of one Mercury year.
MESSENGER has collected a treasure trove of new data from the seven instruments onboard yielding a scientific bonanza; these include extensive global imagery, measurements of the planet’s surface chemical composition, topographic evidence for significant amounts of water ice, magnetic field and interactions with the solar wind, reported the science team at a press conference at NASA Headquarters.
Schematic illustration of the operation of MESSENGER's X-ray Spectrometer (XRS). When X-rays emitted from the Sun’s corona strike the planet, they can induce X-ray fluorescence from atoms at the surface. Detection of these fluorescent X-rays by the XRS allows determination of the surface chemical composition. Credit: NASA/The Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
“We are delighted to share the findings of the first 25% of our year long mission,” said MESSENGER principal investigator Sean Solomon of the Carnegie Institution of Washington at a press briefing for reporters. “We receive new data back almost every day.”
“MESSENGER has snapped over 20,000 images to date,” said Solomon, at up to 10 meters per pixel. The probe has also taken over two million laser-ranging topographic observations, discovered vast volcanic plains, measured the abundances of many key elements and confirmed that bursts of energetic particles in Mercury’s magnetosphere result from the interaction of the planets magnetic field with the solar wind.
“We are assembling a global overview of the nature and workings of Mercury for the first time.”
“We had many ideas about Mercury that were incomplete or ill-formed, from earlier flyby data,” explained Solomon. “Many of our older theories are being cast aside into the dust bin as new observations from new orbital data lead to new insights. Our primary mission has another three Mercury years to run, and we can expect more surprises as our solar system’s innermost planet reveals its long-held secrets.”
Magnetic field lines differ at Mercury's north and south poles As a result of the north-south asymmetry in Mercury's internal magnetic field, the geometry of magnetic field lines is different in Mercury's north and south polar regions. In particular, the magnetic "polar cap" where field lines are open to the interplanetary medium is much larger near the south pole. This geometry implies that the south polar region is much more exposed than in the north to charged particles heated and accelerated by solar wind–magnetosphere interactions. The impact of those charged particles onto Mercury's surface contributes both to the generation of the planet's tenuous atmosphere and to the "space weathering" of surface materials, both of which should have a north-south asymmetry given the different magnetic field configurations at the two poles. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
NASA’s Mariner 10 was the only previous robotic probe to explore Mercury, during three flyby’s back in the mid-1970’s early in the space age.
MESSENGER was launched in 2004 and the mission goal is to produce the first global scientific observations of Mercury and piece together the puzzle of how Mercury fits in with the origin and evolution of our solar system.
There was very little prior imaging coverage of Mercury’s northern polar region.
“We’ve now filled in many of the gaps,” said Messenger scientist Brett Denevi of Johns Hopkins University’s Applied Physics Laboratory (APL). “We now see large smooth plains that are thought to be volcanic in origin.”
“Now we’re seeing for the first time their full extent, which is around 4 million square kilometers (1.54 million square miles). That’s about half the size of the continental United States.” MESSENGER is currently filling in coverage of Mercury’s north polar region, which was seen only partially during the Mariner 10 and MESSENGER flybys. Flyby images indicated that smooth plains were likely important in Mercury’s northernmost regions. MESSENGER's orbital images show that the plains are among the largest expanses of volcanic deposits on Mercury, with thicknesses of several kilometers in many places. The estimated extent of these plains is outlined in yellow. This mosaic is a combination of flyby and orbital coverage in a polar stereographic projection showing latitudes from 50° to 90° N. The longitude at the 6 o'clock position is 0°. Credit: NASA/The Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
“We see all kinds of evidence for volcanism and tectonic deformation of the plains from orbit where we can look straight down,” added Denevi. “In the new images we see ghost craters from pre-existing impact craters that were later covered over by lava.’
Color images of the whole planet – with a resolution of about 1 kilometer per pixel – tell the researchers about the chemical composition and rock types on Mercury’s surface.
“We don’t know the composition yet.”
“We are very excited to study these huge volcanic deposits near the north pole with the implications for the evolution of Mercury’s crust and how it formed,” said Denevi.
“Targeted new high resolution imaging is helping us see landforms unlike anything we’ve seen before on Mercury or the moon.”
MESSENGER’s orbital images have been overlaid on an image from the second flyby shown in Image 1.2a. Even for previously imaged portions of the surface, orbital observations reveal a new level of detail. This region is part of the extensive northern plains, and evidence for a volcanic origin can now be seen. Several examples of “ghost” craters, preexisting craters that were buried by the emplacement of the plains, are seen near the center of the mosaic. Credit: NASA/The Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Determining whether Mercury harbors caches of polar water ice is another one of the many questions the MESSENGER science team hopes to answer.
Two decades ago, Earth-based radar images showed deposits thought to consist of water ice near Mercury’s north and south poles. Researchers postulated a theory that these icy deposits are preserved on the cold, permanently shadowed floors of high-latitude impact craters, similar to those on Earth’s moon.
Early results from topographic measurements are promising.
“The very first scientific test of that hypothesis using Messenger data from orbit has passed with flying colors.”
“The area of possible polar water ice is quite a bit larger than on the moon,” said Solomon. “Its probably meters or more in depth based on radar measurements.”
“And we may have the irony that the planet closest to the sun may have more water ice at its poles than even our own moon.”
“Stay tuned. As this mission evolves, we will be relying on the geochemical and remote sensing instruments which take time to collect observations. The neutron and gamma ray spectrometers have the ability to tell us the identity of these icy materials,” said Solomon.
The same scene as that in Image 1.3a is shown after the application of a statistical method that highlights differences among the eight color filters, making variations in color and composition easier to discern. Credit: NASA/The Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of WashingtonThis topographic contour map was constructed from the several MLA profiles (lines of white circles) that pass through and near the crater circled in Image 3.4. The color scale at right is in km, and north is at the 4 o’clock position. Calculations show that the topography of the crater is consistent with the prediction that the southernmost portion of the crater floor is in permanent shadow. Credit: NASA/The Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of WashingtonA cross-section of Mercury’s magnetosphere (in the noon-midnight plane, i.e., the plane containing the planet-Sun line and Mercury’s spin axis) provides context for the energetic electron events observed to date with the MESSENGER XRS and GRS high-purity germanium (HpGe) detectors. The Sun is toward the right; dark yellow lines indicate representative magnetic field lines. Blue and green lines trace the regions along MESSENGER's orbit from April 2 to April 10 during which energetic electrons were detected and MESSENGER's orbit was within ± 5° of the noon-midnight plane. The presence of events on the dayside, their lack in the southern hemisphere, and their frequency of occurrence at middle northern latitudes over all longitudes point to a more complex picture of magnetospheric activity than found at Earth. Credit: NASA/The Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
It’s been just over two months since the MESSENGER spacecraft successfully entered orbit around Mercury, back on March 18, and it’s been enthusiastically returning image after image of our solar system’s innermost planet at a unprecedented rate. Which, of course, is just fine with us!
The image above shows Mercury’s southern hemisphere and the bright rays of the 50-km-wide crater Han Kan. It was acquired on May 17, 2011.
Below are more recent images from MESSENGER… some of which show regions and features that have never previously been mapped – or even named!
Unnamed double peak-ring basin. Acquired May 13.Detail of the mountains that make up the rim of Caloris Basin. Acquired May 5.Narrow-angle camera view of the 100-km-wide Atget crater. Acquired May 10.Color map of Mercury's surface. The bright crater is Snorri (21km wide). Acquired April 15.
MESSENGER’s orbit about Mercury is highly elliptical, taking it 200 kilometers (124 miles) above its northern surface at the closest pass and 15,193 kilometers (9,420 miles) away from the south pole at furthest. Check out this video showing an animation of how a typical MESSENGER orbit would be executed.
Image credits: Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.
The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft’s seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System’s innermost planet. During the one-year primary mission, MDIS is scheduled to acquire more than 75,000 images in support of MESSENGER’s science goals.
Mercury Astronaut Scott Carpenter speaks in tribute to Alan B. Shepard, first American in Space. Carpenter spoke at the First-Day-of-Issue Stamp dedication ceremony at NASA’s Kennedy Space Center on May 4, 2011. Credit: Ken Kremer
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KENNEDY SPACE CENTER – 50 Years ago this week, Alan B. Shepard became the first American to be launched into space. Shepard blasted off on May 5, 1961 from Cape Canaveral, Florida. NASA and the US Postal Service honored Shepard’s historic achievement today (May 4) at an Official First-Day-of-Issue dedication ceremony at NASA’s Kennedy Space Center in Florida.
Alan Shepard was one of the seven Project Mercury astronauts – who will be collectively known for all eternity as – “The Original 7”.
The US Postal Service simultaneously released two new 44 cent Forever Stamps at today’s commemoration, which bookend two historic space achievements – Shepard’s inaugural manned spaceflight aboard the Mercury capsule and NASA’s unmanned MESSENGER mission which recently became the first probe from Earth to achieve orbit about the Planet Mercury.
Alan Shepard and MESSENGER First-Day-of-Issue Stamp dedication ceremony at NASA’s Kennedy Space Center on May 4, 2011. Alan Shepard is the only American astronaut to be honored with his image on a US postal stamp. Credit: Ken Kremer
Fellow Mercury Astronaut Scott Carpenter attended the ceremony and unveiled the stamps along with Steve Masse, United States Postal Service Vice President of Finance at the Rocket Garden at the KSC Visitor Complex.
Mercury Astronaut Scott Carpenter poses in front of a Mercury Atlas rocket at the Rocket Garden at KSC. Carpenter was propelled to space by the Atlas rocket as the 2nd American to orbit the Earth on May 24, 1962. Credit: Ken Kremer
“Today we celebrate the 50th anniversary of many, many important issues, among them is the first steps from the home planet that were taken by the family of man,” said Carpenter.
Although Shepards suborbital flight aboard the one man “Freedom 7” Mercury capsule lasted barely 15½ minutes, the flight ignited America’s Moon landing effort and propelled American Astronaut Neil Armstrong to become the first human to set foot on the moon on July 20, 1969 during the Apollo 11 mission – one of the crowning technological achievements of the 20th Century.
The success of “Freedom 7” emboldened President John F. Kennedy to declare that America “should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the Earth,” just three weeks later on May 20.
“That was largely a response to Alan’s success,” Carpenter told the crowd of assembled officials, journalists and visitors. Also on hand for the stamp dedication was Shepard’s daughter Laura Shepard Churchly; Charles Bolden, NASA Administrator and former shuttle astronaut; Bob Cabana, KSC Director and former shuttle astronaut; and Jim Adams, NASA deputy director, Planetary Science.
“A decision was made not to put 44 cents on the stamp, but it is forever,” Carpenter emphasized. “It is appropriate to the time we should honor and remember Alan B Shepard and Freedom 7.”
Alan Shepard display at the Kennedy Space Center Visitor Complex. Credit: Ken Kremer
Shepard’s tiny capsule measured just six feet by six feet, reached a maximum speed of 5,100 MPH, roughly eight times the speed of sound, and a zenith of 116 miles above the Earth. Freedom 7 was bolted atop a Redstone rocket that generated only 78,000 pounds of thrust, followed a ballistic arc and landed 300 miles down range in the ocean.
“These stamps, which will go out by the millions across this country, are a testament to the thousands of NASA men and women who shared dreams of human spaceflight and enlarging our knowledge of the universe,” said Bolden.
Shepard’s flight and MESSENGER both blasted off from launch pads quite close to one another at Cape Canaveral Air Force Station which is adjacent to the Kennedy Space Center.
Mercury Astronaut Scott Carpenter is applauded at tribute to Alan B. Shepard, first American in Space ceremony at the Rocket Garden at KSC on May 4, 2011. Credit: Ken Kremer
On Thursday May 5, watch for my on site coverage of NASA’s special ceremony marking the 50th Anniversary of Shepard’s milestone “Freedom 7” mission – and an interview with Scott Carpenter.
Shepard’s mission came barely three weeks after Cosmonaut Yuri Gagarin became the first human to orbit the Earth. The bold flights of these brave Cosmonauts and Astronauts – backed by a few insightful political leaders – began the Era of Human Spaceflight. As the shuttle program winds to a close, the future of US Human Spaceflight is very uncertain.
Read my related articles about Yuri Gagarin and the 50th Anniversary of Human Spaceflight:
Postage stamps honoring Mercury astronaut Alan Shepard, America’s first man in space, and NASA’s MESSENGER probe, the first spacecraft to orbit Mercury, will be presented on May 4th at a public event taking place at the Aviation Heritage Park in Dayton, Ohio.
Alan Shepard poses in his pressure suit before his historic flight on May 5, 1961. Credit: NASA.
The first stamp salutes NASA’s Project Mercury, America’s first manned spaceflight program, and astronaut Alan B. Shepard, Jr.’s historic sub-orbital flight on May 5, 1961 aboard the spacecraft Freedom 7.
The other stamp highlights NASA’s MESSENGER spacecraft currently exploring the planet Mercury. It successfully established orbit around the planet on March 18, 2011, the first spacecraft ever to do so.
These two historic missions frame a remarkable fifty-year period in which the U.S. has advanced space exploration through more than 1,500 manned and unmanned flights.
Both stamps were designed by professional artist Donato Giancola of Brooklyn, NY, who based the stamp designs on NASA photos and images.
Both stamps will be issued as “Forever Stamps” for use in mailing a one-ounce letter. Regardless of when the stamps are purchased and no matter how postage prices may change, these stamps will always be equal to the current First-Class Mail one-ounce price.
NASA's Mercury-Redstone 3 rocket, with Alan Shepard inside the Freedom 7 capsule, launches from Cape Canaveral on May 5, 1961. Credit: NASA.
Stamps are now available online at the US Postal Service store here.
An unnamed crater on Mercury taken by MESSENGER's Narrow Angle Camera. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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Buried treasure on Mercury? If so, I’d look here first. This image shows a currently unnamed crater with an “X” emblazoned on it. The perpendicular lines that cross the crater are secondary crater chains caused by ejecta from two primary impacts outside of the field of view, according to MESSENGER scientists. MESSENGER has been in orbit of Mercury since mid-March of this year, and its Mercury Dual Imaging System (MDIS) pivot and Narrow Angle Camera (NAC) spotted this unusual landform. MESSENGER will be mapping more than 90% of Mercury’s surface as part of a high-resolution surface morphology base map that will be created with MDIS.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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The MESSENGER spacecraft is still happily orbiting Mercury since its orbit insertion in mid-March, and here are some of the latest images sent back from the first rock from the Sun. In this image, the central peaks inside a large crater named Asvaghosa show up as exceptionally bright. The MESSENGER team believes that their high reflectance appears to have been enhanced by the crater rays that cross the area, which originates from another crater. Asvaghosa is 90 km (56 mi.) in diameter, and was targeted for special, high-resolution observations, where MESSENGER’s cameras zero-in for the closest looks possible. While it is not possible to cover all of Mercury’s surface at this high of a resolution during the spacecraft’s one-year mission, several areas of high scientific interest are generally imaged in this mode each week.
See more below!
Oblique view of Bek crater on Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
What a unique, swirling crater — and this high-resolution view of Bek crater (32 km (20 miles) in diameter) has me trying to imagine scaling the cliffs seen in this incredible vista. The MESSENGER team says that the sharp crater rim is in contrast to its subdued surroundings, where crater ejecta scoured the surface and left behind many secondary craters.
'Weird terrain' inside the crater Petrarch on Mercury. Credit: Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
When scientists from the Mariner 10 team first saw this region around Petrarch crater, they called it “weird terrain.” The rugged terrain has an unusual “hilly and lineated” that may have been modified by converging seismic waves and/or ejecta from the formation of the Caloris basin, which is located on the opposite side of the planet. Now, MESSENGER viewed this area under differing lighting conditions than those seen during MESSENGER’s second flyby and Mariner 10’s first pass. The large, smooth area in the upper left is the floor of Petrarch.
Smooth plains on Mercury's northern hemisphere. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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Sharing just a few of the 1,500 images the MESSENGER spacecraft has now taken from its orbital vantage point, mission scientists are understandably excited – if not overwhelmed – by the data being returned from Mercury. “The instruments are all working marvelously and returning data,” said MESSENGER Principal Investigator Sean Solomon. “The imaging system was turned on earlier this week and over 1,500 images will be acquired over a 3 day period. That is more images than were taken during any of the flybys by the spacecraft.”
Solomon said some of the first images were taken precisely 37 years after the first spacecraft flew by Mercury, Mariner 10 in 1974. “We have now closed the loop begun by Mariner 10, culminating with the first insertion of a spacecraft in orbit.”
2,430 days ago the MESSENGER lifted off from Earth, and after three flybys and a nearly 5 billion mile journey, the spacecraft’s thrusters fired for 15 minutes back on March 17, enabling the spacecraft to ease into orbit.
While already finding intriguing features – many which pose more questions than answers, Solomon reminded reporters during a press conference call today that “all the big questions about Mercury are meant to be answered in a year of observations, not just a couple of days, so we’ll look forward to what is yet to come.”
The top image shows an area of Mercury’s north polar region, revealing terrain that had not been previously seen by spacecraft. The long shadows also accentuate the topography of the surface, which includes a number of ridges, but an unusually smooth surface. Solomon said understanding the interiors of the craters in Mercury’s polar regions and any ices they may contain is one of the main science goals of the MESSENGER mission. “Radar images of Mercury that are now 20 years old suggested that water ice could be in the interiors of these craters,” Solomon said. “That is a hypothesis we’ve been aching to test for 20 years, and now we’ll be able to peer into those crater floors.”
This WAC image showing a never-before-imaged area of Mercury’s surface was taken from an altitude of ~450 km (280 miles) above Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
This is another region never seen before by spacecraft. “This is probably a plain deposit formed by undulating ridges and a host of secondary craters formed when a large crater was formed out of the field of view,” Solomon said. “We’re seeing that secondary craters (those formed from the ejecta of another crater) are very pervasive across the surface.”
Solomon added that they are seeing secondary craters that are larger than most secondary craters, compared to those on the Moon and other planetary bodies. “They are surprisingly large,” he said. “ A lot of questions raised by images taken so far and have a large menu of questions we’ll be pursuing over the mission.”
Beautiful bright crater on Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
The crater near the bottom of this image is a beautiful example of a relatively small, simple, fresh impact feature on Mercury.The bright ejecta and rays are symmetrically distributed around the crater, indicating that the body that struck Mercury to form the crater approached on a path that was not highly inclined from the vertical.
MESSENGER Systems engineer Eric Finnegan told reporters that it takes about 6 minutes for data to be relayed from the spacecraft to Earth, as Mercury (and the spacecraft) is about .71 AU away, the equivalent of about 106 million km (66 million miles). MESSENGER is in an elliptical orbit, and at its closest point in orbit (periapsis) is about 250 km away from Mercury, and at its farthest point (apoapsis) is about 1,500 km away.
Wide Angle Camera color image of Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
This is one of the first color images from MESSENGER in orbit. Solomon said the Wide Angle Camera is not a typical color camera. It can image in 11 colors, ranging from 430 to 1020 nm wavelength (visible through near-infrared). “We will be taking global images in at least 8 filters to get a sense of the color variation, which shows the variations in composition and depth of surface features exposed by the action of impact cratering from Mercury’s history.”
From Orbit, Looking toward Mercury's Horizon. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Images like this were frequently seen during MESSENGER’s three flybys. But now that the spacecraft is in orbit of Mercury, views of Mercury’s horizon in the images will be much less common. Occasionally, however, in order to obtain images of a certain portion of Mercury’s surface, the horizon will also be visible. But Solomon said MESSENGER’s goal is to get a set of global data for the planet. “An entire global perspective is unfolding and will continue to unfold over next few months,” he said.
Bright rays, consisting of impact ejecta and secondary craters, spread across this NAC image and radiate from Debussy crater, located at the top. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
This is a closeup Debussy Crater, which was the object of the first image released by MESSENGER yesterday. When asked about the age of this crater, Solomon said it is difficult to give a hard age to craters on Mercury due to not having samples in hand, like to do for the Moon. “On the moon ones that are bright like this, such as Copernicus, were formed in the last 20% in the history of the planet. We see only a handful of bright craters like Debussy on Mercury.”
“When you see a crater that is so bright,” Solomon continued, “ it is because it has not gone through the process of space weathering, completely. Brightness of craters identifies them as being younger than the rest of the terrain, as it hasn’t had the time to have their characteristics altered by age, as those of us with gray hair know.”
Solomon said Debussy was likely created by in impact of an object 5-10 km across.
“Orbits of most asteroids and comets that encounter Mercury are traveling at a much higher speed than planetary bodies farther out from the Sun, and that shows in the amount of melt shown in the surface of Mercury. But still a lot we have to learn about that. Craters at different states of decay and degradation will tell us more about this.”
Altimetric profiles obtained on 29 March during the first two successive MESSENGER orbits on which the Mercury Laser Altimeter (MLA) instrument was operating. Credit: NASA/Goddard Space Flight Center/MIT/Johns Hopkins University Applied Physics Laboratory
This graph shows the first two topographic profiles that were obtained from orbit by the Mercury Laser Altimeter (MLA). “This shows rich detail that we’ve just begun to analyze,” Solomon said, “showing exquisite detail, and we’ll be able to see the topography at both scales of individual geological features and global regions.”
This plot depicts measurements of the strength of Mercury's internal magnetic field measured on 10 successive MESSENGER orbits. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
One big question is about Mercury’s magnetic field. This illustrates the measurements made from 10 orbits of MESSENGER’s magnetometer. In a span of 5 days, messenger has tripled the mount of observations of the planet’s magnetic field, so Solomon said the science team is quickly ramping up a much larger data set to see the geometry of Mercury’s magnetic field, which might help explain why the solar system’s smallest planet still has a magnetic field when the larger planets Mars and Venus do not.
Moreover, because of MESSENGER’s orbit, the maximum magnitude of the measured field was greater than that seen during any of the spacecraft flybys. Solomon said these observations are improving our understanding of Mercury’s magnetic field and how its magnetosphere can change over timescales of minutes, how the solar activity and interaction between the Sun and the planet affect the magnetic field.
“As the Sun’s activity ramps up, it is an exciting time to be at Mercury and have a ringside perspective,” Solomon said.
MESSENGER's first image from Mercury orbit, with the bright Debussy crater visible at upper right. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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Here it is, the first image taken by the MESSENGER spacecraft since entering orbit around Mercury on March 17, and it includes portions of the planet not yet previously seen by spacecraft. The image was taken on today, March 29, 2011 at 5:20 am EDT by the Mercury Dual Imaging System as the spacecraft sailed high above Mercury’s south pole. The dominant rayed crater in the upper portion of the image is Debussy, and the smaller crater Matabei with unusual dark rays is visible to the west of Debussy. The bottom portion of this image near Mercury’s south pole is new territory, with MESSENGER being the first spacecraft to image this region of Mercury.
After capturing its first image, MESSENGER acquired an additional 363 images during six hours 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.
The image was acquired as part of the orbital commissioning phase of the MESSENGER mission. Over the next three days, the spacecraft will acquire 1,185 additional images in support of MDIS commissioning-phase activities. Continuous global mapping of Mercury will begin on April 4.
“The entire MESSENGER team is thrilled that spacecraft and instrument checkout has been proceeding according to plan,” says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. “The first images from orbit and the first measurements from MESSENGER’s other payload instruments are only the opening trickle of the flood of new information that we can expect over the coming year. The orbital exploration of the Solar System’s innermost planet has begun.”
Several other images will be released tomorrow, March 30, in conjunction with a media teleconference. We’ll get them posted as quickly as possible!
An image of Mercury’s tail obtained from combining a full day of data from a camera aboard the STEREO-A spacecraft. The reflected sunlight off the planet's surface results in a type of over-exposure that causes Mercury to appear much larger than its actual size. The tail-like structure extending anti-sunward from the planet is visible over several days and spans an angular size exceeding that of a full Moon in the night sky. Credit: Boston University
The STEREO mission to study the Sun also has observed some unusual comet-like features exhibited by the planet Mercury, with a coma of tenuous gas surrounding the planet and a very long tail extending away from the sun. These types of features had been seen before from telescopes on Earth, but the STEREO observations are helping scientists to understand the nature of the emissions coming from Mercury, which might be different from what was previously thought.
Another note of interest: the tail in the STEREO data was actually discovered by a fellow blogger, Ian Musgrave, who writes Astroblog. He is a medical researcher in Australia who has a strong interest in astronomy. Viewing the on-line data base of STEREO images and movies, Dr. Musgrave recognized the tail and sent news of it to a team of astronomers from Boston University to compare it with their observations.
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The STEREO mission has two satellites placed in the same orbit around the Sun that the Earth has, but at locations ahead and behind it. This configuration offers multi-directional views of the electrons and ions that make up the escaping solar wind. On occasion, the planet Mercury appears in the field of view of one or both satellites. In addition to its appearance as a bright disk of reflected sunlight, a ‘tail’ of emission can be seen in some of the images.
From Earth-based telescopes, astronomers have seen how the Sun’s radiation pressure pushes sodium atoms from Mercury’s surface away from the planet – and away from the Sun – creating a tail that extends many hundreds of times the physical size of Mercury.
Much closer to Mercury, several smaller tails composed of other gases, both neutral and ionized, have been found by NASA’s MESSENGER satellite as it flew by Mercury in its long approach to entering into a stable orbit there.
“We have observed this extended sodium tail to great distances using our telescope at the McDonald Observatory in Texas,” Boston University graduate student Carl Schmidt explained, “and now the tail can also be seen from satellites near Earth.”
“What makes the STEREO detections so interesting is that the brightness levels seem to be too strong to be from sodium,” said Boston University graduate student Carl Schmidt, lead author on a paper that was presented at European Planetary Science Congress in Rome this week.
Now, the Boston University scientists are working with the STEREO scientists to try and sort everything out.
The current focus of the team is to sort out all of the possibilities for the gases that make up the tail. Dr. Christopher Davis from the Rutherford Appleton Laboratory in Chilton, England, a member of the STEREO team is working closely with the Boston University group on refining the brightness calibration methods, and determining the precise wavelengths of light that would get through the cameras’ filters.
“The combination of our ground-based data with the new STEREO data is an exciting way to learn as much as possible about the sources and fates of gases escaping from Mercury,” said Michael Mendillo, Professor of Astronomy at Boston University and director of the Imaging Science Lab where the work is being done.
“This is precisely the type of research that makes for a terrific Ph.D. dissertation,” Mendillo added.
