NASA MESSENGER Captures Images of Ice on Mercury

Nasa's MESSENGER spacecraft

NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft has provided the first optical images of ice and other frozen volatile materials within permanently shadowed craters near Mercury's north pole.

The images not only reveal the morphology of the frozen volatiles, but they also provide insight into when the ices were trapped and how they've evolved, according to an article published in the journal, Geology.

Two decades ago, Earth-based radar images of Mercury revealed the polar deposits, postulated to consist of water ice.

Prokofiev, named in August 2012 for the Russian composer, is the largest crater in Mercury’s north polar region to host radar-bright material.

Credit: NASA /Johns Hopkins University Applied Physics Lab /Carnegie Iinstitution of Washington

That hypothesis was later confirmed by MESSENGER through a combination of neutron spectrometry, thermal modeling, and infrared reflectometry.

"But along with confirming the earlier idea, there is a lot new to be learned by seeing the deposits," said lead author Nancy Chabot, the Instrument Scientist for MESSENGER's Mercury Dual Imaging System (MDIS) and a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

Beginning with MESSENGER's first extended mission in 2012, scientists launched an imaging campaign with the broadband clear filter of MDIS's wide-angle camera (WAC).

Mercury Dual Imaging System (MDIS)

Although the polar deposits are in permanent shadow, through many refinements in the imaging, the WAC was able to obtain images of the surfaces of the deposits by leveraging very low levels of light scattered from illuminated crater walls. "It worked in spectacular fashion," said Chabot.

The team zeroed in on Prokofiev, the largest crater in Mercury's north polar region found to host radar-bright material.

"Those images show extensive regions with distinctive reflectance properties," Chabot said.

"A location interpreted as hosting widespread surface water ice exhibits a cratered texture indicating that the ice was emplaced more recently than any of the underlying craters."

In other areas, water ice is present, she said, "but it is covered by a thin layer of dark material inferred to consist of frozen organic-rich compounds." In the images of those areas, the dark deposits display sharp boundaries.

"This result was a little surprising, because sharp boundaries indicate that the volatile deposits at Mercury's poles are geologically young, relative to the time scale for lateral mixing by impacts," said Chabot.

"One of the big questions we've been grappling with is 'When did Mercury's water ice deposits show up?' Are they billions of years old, or were they emplaced only recently?" Chabot said.

"Understanding the age of these deposits has implications for understanding the delivery of water to all the terrestrial planets, including Earth."

Overall, the images indicate that Mercury's polar deposits either were delivered to the planet recently or are regularly restored at the surface through an ongoing process.

The images also reveal a noteworthy distinction between the Moon and Mercury, one that may shed additional light on the age of the frozen deposits.

"The polar regions of Mercury show extensive areas that host water ice, but the Moon's polar regions, which also have areas of permanent shadows and are actually colder, look different," Chabot said.

"One explanation for differences between the Moon and Mercury could be that the volatile polar deposits on Mercury were recently emplaced," according to the paper.

"If Mercury's currently substantial polar volatile inventory is the product of the most recent portion of a longer process, then a considerable mass of volatiles may have been delivered to the inner Solar System throughout its history."

"That's a key question," Chabot said. "Because if you can understand why one body looks one way and another looks different, you gain insight into the process that's behind it, which in turn is tied to the age and distribution of water ice in the Solar System. This will be a very interesting line of inquiry going forward."

NASA Messenger: Mercury Mission - 10 Years in Space

In celebration of the 10th anniversary of its launch, the MESSENGER team released this movie showing a flyover of Mercury. The movie is sped up by a factor of seven for ease of viewing.

Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory

Ten years ago, on August 3, 2004, NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft blasted off from Cape Canaveral, Florida, for a risky mission that would take the small satellite dangerously close to Mercury’s surface, paving the way for an ambitious study of the planet closest to the Sun.

The spacecraft traveled 4.9 billion miles (7.9 billion kilometers), a journey that included 15 trips around the Sun and flybys of Earth once, Venus twice, and Mercury three times, before it was inserted into orbit around its target planet in 2011.

“We have operated successfully in orbit for more than three Earth years and more than 14 Mercury years as we celebrate this amazing 10th anniversary milestone,” said MESSENGER Mission Operations Manager Andy Calloway, of the Johns Hopkins University Applied Physics Laboratory (APL).

“The MESSENGER spacecraft operates in one of the most challenging and demanding space environments in our Solar System, and we have met that challenge directly through innovation and hard work, as exemplified by the stunning discoveries and data return achievements.

Our only regret is that we have insufficient propellant to operate another 10 years, but we look forward to the incredible science returns planned for the final eight months of the mission.”

MESSENGER captured the images in the flyover movie during this flight path over Mercury's north polar region.

Image Credit: NASA

MESSENGER is only the second spacecraft sent to Mercury. Mariner 10 flew past it three times in 1974 and 1975 and gathered detailed data on less than half the surface.

MESSENGER took advantage of an ingenious trajectory design, lightweight materials, and miniaturisation of electronics, all developed in the three decades since Mariner 10 flew past Mercury.

“It was quite challenging to design and execute a trajectory that could culminate in Mercury orbit,” said Mission and Spacecraft Systems Engineer Dan O’Shaughnessy, of APL.

“Designing an attendant spacecraft that was light enough to carry the necessary propellant to execute such a trajectory with enough room left over for a payload capable of global characterisation of the planet is an impressive accomplishment.”

Additionally, he said, “the team’s concept of operations that streamlines planning while optimizing the use of our payload. despite substantial thermal and power constraints, is an amazing feat.”

MESSENGER Deputy Principal Investigator Larry Nittler, of the Carnegie Institution of Washington, said that the mission has rewritten scientists’ understanding of the planet “and given us plenty of surprises.”

“Geochemical measurements have revealed a surface poor in iron, but rich in moderately volatile elements such as sulphur and sodium,” said Nittler.

“These results rule out some long-standing theories put forward to explain Mercury’s anomalously high density compared with the other planets in the inner solar system,” he explained.

“Maps of elemental abundances show that the interior is highly chemically heterogeneous, providing important clues to the early geological history of the planet.”

“MESSENGER observations have also shown that Mercury’s surface was shaped by volcanic activity, identified unique landforms shaped by loss of volatile materials, and confirmed the presence of large amounts of water ice protected from the Sun’s heat within permanently shadowed impact craters near the planet’s poles, said Nittler

Infographic with statistics on the MESSENGER mission.

Image Credit: NASA

“We have found that the complex interplay of the interplanetary magnetic field with that of Mercury results in a remarkably dynamic electromagnetic environment surrounding the planet, including unexplained bursts of electrons and highly variable distributions of different elements in the thin exosphere,” Nittler added.

“Over the next few months, MESSENGER will observe Mercury at lower altitudes and thus smaller spatial scales than ever before, and this is sure to result both in exciting scientific discoveries and new puzzles about our solar system’s enigmatic innermost planet.”

In celebration of the 10th anniversary of its launch, the MESSENGER team has released a movie acquired during an early stage of MESSENGER’s low-altitude campaign.

Messenger narrow-angle camera (NAC)

The movie provides a bird’s-eye view of what the spacecraft sees as it flies over the planet at close range and was assembled from 214 images taken by the narrow-angle camera (NAC) on June 8, 2014.

The NAC’s field of view looked toward the horizon along the direction of MESSENGER's motion as the probe crossed the terminator into night.

Scott Murchie

“This view is what a traveller on the MESSENGER spacecraft might see during low-altitude operations in the coming year,” noted MESSENGER Co-Investigator Scott Murchie of APL.

“During the final phase of its mission, MESSENGER's science instruments will use low-altitude operations like this to explore the surface and subsurface of Mercury at unprecedented resolution.”

The image frames were taken once per second while MESSENGER was at altitudes ranging from 115 to 165 kilometers, traveling at a speed of 3.7 kilometers per second relative to the surface. The movie is sped up by a factor of six for ease of viewing.

Read the full article here

NASA Messenger MDIS Image: Mercury's Caloris basin in sharp relief - Video

Mercury’s uneven surface comes into sharp relief when the sun sits low on the planet’s eastern horizon. 

The relatively smooth floor of the Caloris basin lies on the right, with the rim and exterior of the basin to the left. 

The knobby texture outside of the basin may have arisen due to blocks of material ejected by the basin-forming impact. 

MESSENGER spacecraft acquired this image as part of the Mercury Dual Imaging System (MDIS) high-incidence-angle base map. 

High incidence angles, obtained when the sun sits near the horizon, create long shadows that accentuate the small-scale topography of geologic features, as seen here.

This animation shows 89 wide-angle camera (WAC) images of Mercury’s south polar region acquired by the Mercury Dual Imaging System (MDIS) over one complete Mercury solar day (176 Earth days).

This dataset enabled the illumination conditions at Mercury’s south polar region to be quantified, producing the map seen at the end of the movie and provided as a separate image.

The map is coloured on the basis of the percentage of time that a given area is sunlit; areas appearing black in the map are regions of permanent shadow.

The movie and illumination map are shown in polar stereographic projection, extending northward to 73° S, and 0° longitude is at the top. The large crater near Mercury’s south pole, Chao Meng-Fu, has a diameter of 180 km.

NASA MESSENGER: False-Colour Image of Earth Highlights Plant Growth

On Aug. 3, 2004, NASA’s Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft began a seven-year journey, spiraling through the inner solar system to Mercury. 

One year after launch, the spacecraft zipped around Earth, getting an orbit correction from Earth’s gravity and getting a chance to test its instruments by observing its home planet.

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

This image is a view of South America and portions of North America and Africa from the Mercury Dual Imaging System’s (MDIS) wide-angle camera aboard MESSENGER.

MDIS, records light at eleven different wavelengths, including visible and infrared light. Combining blue, red, and green light results in a true-colour image from the observations.

The image substitutes infrared light for blue light in the three-band combination.

The resulting image is crisper than the natural colour version because our atmosphere scatters blue light.

Infrared light, however, passes through the atmosphere with relatively little scattering and allows a clearer view. That wavelength substitution makes plants appear red. Why?

Plants reflect near-infrared light more strongly than either red or green, and in this band combination, near-infrared is assigned to look red.

Apart from getting a clearer image, the substitution reveals more information than natural colour.

Healthy plants reflect more near-infrared light than stressed plants, so bright red indicates dense, growing foliage.

For this reason, biologists and ecologists occasionally use infrared cameras to photograph forests.

NASA MESSENGER Surpasses 200,000 Orbital Images of Mercury

This image was acquired as part of the MDIS low-altitude imaging campaign. 

During MESSENGER's second extended mission, the spacecraft makes a progressively closer approach to Mercury's surface than at any previous point in the mission, enabling the acquisition of high-spatial-resolution data. 

For spacecraft altitudes below 350 kilometers, NAC images are acquired with pixel scales ranging from 20 meters to as little as 2 meters. 

Credit: NASA

MESSENGER has now returned more than 200,000 images acquired from orbit about Mercury.

The 1996 proposal for the mission promised a return of at least 1,000 images says Robert Gold, MESSENGER's Science Payload Manager.

Robert Gold

"We expected then that we would have some data compression that would probably raise the image total to somewhere near 2,000 images," says Gold, of the Johns Hopkins University Applied Physics Laboratory (APL), but scientists did not imagine then the degree to which MESSENGER would surpass that goal.

"Returning over 200,000 images from orbit about Mercury is an impressive accomplishment for the mission, and one I've been personally counting down for the last few months," says APL's Nancy Chabot, the Instrument Scientist for the Mercury Dual Imaging System (MDIS).

"However, I'm really more excited about the many thousands of images that are still in MESSENGER's future, especially those that we plan to acquire at low altitudes and will provide the highest resolution views yet of Mercury's surface."

During MESSENGER's second extended mission, the spacecraft is making a progressively closer approach to Mercury's surface with each successive orbit.

In about two months, each closest approach will be at a lower altitude than at any previous point in the mission, enabling the acquisition of unprecedentedly high-spatial-resolution data.

For spacecraft altitudes below 350 kilometers, Narrow Angle Camera (NAC) images will be acquired with pixel scales ranging from 20 meters to as little as 2 meters.

Nancy Chabot

To commemorate the milestone, image scientists released this four-image mosaic—one of the first from the MDIS low-altitude imaging campaign—that reveals, among other features, hollows that appear to have formed in one layer in the wall of this 15-kilometer-diameter crater.

The mission marks three additional milestones today: the spacecraft concludes its 12th Mercury year in orbit, its 18th Mercury sidereal day in orbit, and its 6th Mercury solar day in orbit.

"We have come an incredible way since the first mission proposal was submitted to NASA just over 17 years ago," notes MESSENGER Project Scientist Ralph McNutt of APL.

"Getting to launch and then to Mercury, flyby by flyby, and into orbital operations were incredible accomplishments—against all sorts of odds—and yet we are now, almost routinely, noting these statistics about the mission that has literally revealed an entirely new world to humanity."

When MESSENGER was launched in August 2004, he continues, "none of the team in their wildest imagination could have foreseen the successes that we now celebrate with new data coming back week by week from the innermost planet. And we are not done.

With a little more than a year left to go, before gravity brings the end to operations, we will view the planet and its environment from altitudes lower than were ever envisioned only a few short years ago—and, as with any planetary mission providing closer and closer looks at a planetary neighbour, all we can guess is that we have not wrung all of Mercury's surprises and discoveries just yet."

NASA Messenger: Sunlight on the Side of the Planet Mercury

Another day, another beautiful view of Mercury's horizon. 

In this scene, which was acquired looking from the shadows toward the sunlit side of the planet, a 120-km (75 mi.) impact crater stands out near the center.

Emanating from this unnamed crater are striking chains of secondary craters, which gouged linear tracks radially away from the crater.

While this crater is not especially fresh (its rays have faded into the background), it does appear to have more prominent secondary crater chains than many of its peers.

This image was acquired on Oct. 2, 2013 by the Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS) aboard NASA's MESSENGER spacecraft, as part of the MDIS's limb imaging campaign.

Once per week, MDIS captures images of Mercury's limb, with an emphasis on imaging the southern hemisphere limb.

These limb images provide information about Mercury's shape and complement measurements of topography made by the Mercury Laser Altimeter (MLA) of Mercury's northern hemisphere.

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 first two years of orbital operations, MESSENGER acquired over 150,000 images and extensive other data sets. MESSENGER is capable of continuing orbital operations until early 2015.

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

NASA Messenger: A View of Mercury by MDIS

This image of Mercury, acquired by the Mercury Dual Imaging System (MDIS) aboard NASA's MESSENGER mission on April 23, 2013, allows us to take a step back to view the planet.

Prior to the MESSENGER mission, Mercury's surface was often compared to the surface of Earth's moon, when in fact, Mercury and the moon are very different.

This image in particular highlights many basins near Mercury's terminator, including Bach crater. 

Many craters with central peaks and the nearby bright rays of Han Kan crater are also evident.

Once per week, MDIS captures images of Mercury's limb, with an emphasis on imaging the southern hemisphere limb.

These limb images provide information about Mercury's shape and complement measurements of topography made by the Mercury Laser Altimeter (MLA) of Mercury's northern hemisphere.

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