MESSENGER 2011 - A Year in Review

As we prepare to bid farewell to 2011, the MESSENGER spacecraft is now nine months into its orbital mission. The scientific products that MESSENGER has returned have given planetary scientists and space enthusiasts around the world a chance to better understand Mercury's formation, surface composition, and unique atmosphere-magnetosphere system. The Mercury Dual Imaging System (MDIS) has captured >99.9% of Mercury's surface in high resolution, including previously unseen terrain. As the mission moves forward into 2012, we are excited to continue to unravel the mysteries of this planet of extremes. Let's take a look back at some of this year's highlights:

January: Are we there yet?
February: Getting closer... A Solar System Family Portrait, from the Inside Out (second row)
March: Mercury Orbit Insertion! First Image Ever Obtained from Mercury Orbit (top left)
April: X Marks the Spot (top middle)
May: Another Look at Atget (top right)
June: What Happens in Degas Stays in Degas (bottom left)
July: Memories of Many Mixed Materials (third row, middle)
August: A Crater in CloseUp (third row, left)
September: Stunning Landforms in Raditladi Basin (third row, right)
October: The First Solar Day (fourth row, left)
November: Hurrah for the Red and the Blue (fourth row, right)
December: The Bright Rays of Mena (bottom middle), and Mercury Globe: North Pole (bottom right)

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

Inside Eminescu Crater

This oblique view shows a portion of the rim of the crater Eminescu. The angle of this image provides a great perspective for viewing the spectacular cliffs that formed as material slumped from the crater rim into the crater interior, as well as small ponds of impact melt perched on the rim. North is down in this image.

Date acquired: December 05, 2011
Image Mission Elapsed Time (MET): 231611014
Image ID: 1099316
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 9.8°
Center Longitude: 115.5° E
Resolution: 34 meters/pixel
Scale: The scene is approximately 35 km (22 miles) from north to south.
Incidence Angle: 65.1°
Emission Angle: 60.1°
Phase Angle: 125.3°

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

When the Going Gets Weird, the Weird Turn Pro

This view is a close-up of an area featured in a previous Gallery image. The region is located diametrically opposite the Caloris impact basin, and has been affected by converging seismic waves or ejecta that caused the peculiar "hilly and lineated" texture. Members of the Mariner 10 team informally called this the "weird terrain" when it was first discovered in 1974.

Date acquired: August 02, 2011
Image Mission Elapsed Time (MET): 220756231
Image ID: 581158
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -29.92°
Center Longitude: 342.0° E
Resolution: 235 meters/pixel
Scale: The scene is about 248 km (155 mi.) across.
Incidence Angle: 85.4°
Emission Angle: 19.3°
Phase Angle: 104.7°

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

A Small Pond

This image shows a small pond of impact melt that was ejected from a crater just out of view. The melt ponded in this low, forming a smooth surface similar to the melt ponds south of Kuiper crater. North is toward the upper right corner.

Date acquired: November 06, 2011
Image Mission Elapsed Time (MET): 229105038
Image ID: 980525
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 63.9°
Center Longitude: 256.5° E
Resolution: 16 meters/pixel
Scale: The smooth region is approximately 3 km (1.9 miles) across
Incidence Angle: 69.5°
Emission Angle: 15.6°
Phase Angle: 85.2°

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

Rays of Light Material

The ejecta of this fresh 20-km impact crater swept the surface, leaving beautiful bright rays. Crater rays fade with time as smaller impacts mix them into the surrounding soil and particles from the solar wind change the surface's chemistry. Given a little time (perhaps a million years or so), this crater will look like the other similar-sized craters in the frame.

Date acquired: November 17, 2011
Image Mission Elapsed Time (MET): 230018573
Image ID: 1023529
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -51.0°
Center Longitude: 175.1° E
Resolution: 221 meters/pixel
Scale: The rayed crater is approximately 20 km (12 miles) in diameter
Incidence Angle: 53.1°
Emission Angle: 37.8°
Phase Angle: 78.6°

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

Fram Rupes

One hundred years ago, on December 14, 1911, Norwegian explorer Roald Amundsen and his party became the first people to reach the Earth's south pole. The name of the ship that carried Amundsen to Antarctica was the Fram. The image above shows a portion of Fram Rupes on the planet Mercury, a long scarp (cliff) formed by compressive forces generated as the planet's interior cooled and contracted.

Date acquired: November 06, 2011
Image Mission Elapsed Time (MET): 229066087
Image ID: 978519
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -55.5°
Center Longitude: 267.8° E
Resolution: 152 meters/pixel
Scale: The edges of the image are about 157 km long.
Incidence Angle: 67.2°
Emission Angle: 14.9°
Phase Angle: 81.2°

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

The Bright Rays of Mena

The young rays of Mena crater contrast brightly against the surrounding surface, though the rays will gradually fade with time. The asymmetric pattern of the rays, with a gap in the south-western direction, may be due to the angle at which the impact that formed the crater occurred, or to the fact that Mena formed on the rim of a larger pre-existing impact crater, as seen in this image.

Date acquired: November 12, 2011
Image Mission Elapsed Time (MET): 229581348, 229581352, 229581356
Image ID: 1003074-1003076
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filters: 9, 7, 6 (1000, 750, 430 nanometers) as red, green, blue
Center Latitude: -0.97°
Center Longitude: 234.0° E
Resolution: 257 meters/pixel
Scale: Mena has a diameter of 15 km (9 miles)
Incidence Angle: 29.7°
Emission Angle: 16.3°
Phase Angle: 46.0°

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

Kertesz Crater Anaglyph

This is an anaglyph created from two images of the crater Kertesz. By viewing images obtained from slightly different perspectives through red-blue glasses, the brain perceives a "3-D" image. The red lens should be on the left eye. With this anaglyph, better results may be achieved by tilting the head slightly to the left. The floor of Kertesz is covered with spectacular hollows. See more images of hollows here (scroll down to "Presenter #2").

Date acquired: July 31, 2011
Image Mission Elapsed Time (MET): 220634378 and 220591163
Image ID: 575037 and 573112
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 27.4°
Center Longitude: 146.1° E
Resolution: 17 meters/pixel
Scale: Kertesz crater is about 31 km (19 mi.) in diameter.
Incidence Angle: 76.4° and 75.0°
Emission Angle: 30.3° and 40.9°
Phase Angle: 106.7° and 115.9°

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

Spanish Bombs

The small crater at the left side of this image is named for Juan de Mena, a Spanish poet of the 15th century. Mena has extensive bright rays, which can be better appreciated in the global map of Mercury (right on the equator, part way in from the left). Mena formed on the rim of an existing crater, which may help to explain the asymmetric pattern of Mena's rays.

Date acquired: April 19, 2011
Image Mission Elapsed Time (MET): 211718303
Image ID: 151162
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -0.24°
Center Longitude: 236.3° E
Resolution: 254 meters/pixel
Scale: The image is about 138 km (85 mi.) wide.
Incidence Angle: 65.9°
Emission Angle: 22.3°
Phase Angle: 43.6°

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

Complex Craters

While many of the most spectacular craters on Mercury are young and rayed, the vast majority are older and have been modified by both internal and external forces over time. The large 90-km crater in this image has been deformed by a lobate scarp and battered by craters up to 30 km in diameter.

Date acquired: October 27, 2011
Image Mission Elapsed Time (MET): 228200113
Image ID: 937596
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 5.65°
Center Longitude: 321.9° E
Resolution: 104 meters/pixel
Scale: The large crater in this scene is approximately 90 km (56 miles) in diameter
Incidence Angle: 69.2°
Emission Angle: 66.8°
Phase Angle: 102.0°

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

Hollowed Crater

The crater at the center of this image is home to more of the "hollows" that dot Mercury's surface, which appear here as high-reflectance features near the crater's central peak and around its floor-wall boundary. This crater, which does not yet have an official name, was also seen in an early image that MESSENGER captured during the spacecraft's first imaging orbit around Mercury.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

Date acquired: October 21, 2011
Image Mission Elapsed Time (MET): 227644286
Image ID: 911007
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: -1.98°
Center Longitude: 354.1° E
Resolution: 337 meters/pixel
Scale: The crater at center is approximately 90 km (56 miles) across
Incidence Angle: 79.6°
Emission Angle: 56.2°
Phase Angle: 135.9°

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

Strange Hollows Discovered on Mercury

NASA's MESSENGER spacecraft has discovered strange hollows on the surface of Mercury. Images taken from orbit reveal thousands of peculiar depressions at a variety of longitudes and latitudes, ranging in size from 60 feet to over a mile across and 60 to 120 feet deep. No one knows how they got there.

"These hollows were a major surprise," says David Blewett, science team member from the Johns Hopkins University Applied Physics Laboratory. "We've been thinking of Mercury as a relic – a place that's really not changing much anymore, except by impact cratering. But the hollows appear to be younger than the craters in which they are found, and that means Mercury's surface is still evolving in a surprising way."

Mars Reconnaissance Orbiter spotted similar depressions in the carbon dioxide ice at Mars' south pole, giving that surface a "swiss cheese" appearance. But on Mercury they're found in rock and often have bright interiors and halos.

"We've never seen anything quite like this on a rocky surface."

If you could stand in one of these "sleepy" hollows on Mercury's surface, you'd find yourself, like Ichabod Crane, in a quiet, still, haunting place, with a black sky above your head.

"There's essentially no atmosphere on Mercury," explains Blewett. "And with no atmosphere, wind doesn't blow and rain doesn't fall. So the hollows weren't carved by wind or water. Other forces must be at work."

As the planet closest to the Sun, Mercury is exposed to fierce heat and extreme space weather. Blewett believes these factors play a role.

A key clue, he says, is that many of the hollows are associated with central mounds or mountains inside Mercury's impact craters. These so-called “peak rings” are thought to be made of material forced up from the depths by the impact that formed the crater. Excavated material could be unstable when it finds itself suddenly exposed at Mercury's surface.

"Certain minerals, for example those that contain sulfur and other volatiles, would be easily vaporized by the onslaught of heat, solar wind, and micrometeoroids that Mercury experiences on a daily basis," he says. "Perhaps sulfur is vaporizing, leaving just the other minerals, and therefore weakening the rock and making it spongier. Then the rock would crumble and erode more readily, forming these depressions."

MESSENGER has indeed proven Mercury unexpectedly rich in sulfur. That in itself is a surprise that's forcing scientists to rethink how Mercury was formed. The prevailing models suggest that either (1) very early in Solar System history, during the final sweep-up of the large planetesimals that formed the planets, a colossal impact tore off much of Mercury's rocky outer layering; or (2) a hot phase of the early Sun heated up the surface enough to scorch off the outer layers. In either case, the elements with a low boiling point – volatiles like sulfur and potassium – would have been driven off.

But they're still there.

"The old models just don't fit with the new data, so we'll have to look at other hypotheses."

To figure out how the planets and Solar System came to be, scientists must understand Mercury.

"It's the anchor at one end of the Solar System. Learning how Mercury formed will have major implications for the rest of the planets. And MESSENGER is showing that, up to now, we've been completely wrong about this little world in so many ways!"

What other surprises does Mercury hold? The sleepy hollows of the innermost planet may be just the beginning.

Photo credit (top):   NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington; (bottom):  Science/AAAS

Mapping Beethoven

At top, the white line highlights 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 21° S, 236° 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.

Below, smooth plains within the same area have been 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.

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

The Interior of Kuiper

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

This image was acquired as part of MDIS's high-resolution surface morphology base map. The surface morphology base map will cover more than 90% of Mercury's surface with an average resolution of 250 meters/pixel (0.16 miles/pixel or 820 feet/pixel). Images acquired for the surface morphology base map typically have off-vertical Sun angles (i.e., high incidence angles) and visible shadows so as to reveal clearly the topographic form of geologic features.

Date acquired: May 04, 2011
Image Mission Elapsed Time (MET): 212983376
Image ID: 210557
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: -12.33°
Center Longitude: 331.2° E
Resolution: 309 meters/pixel
Scale: Kuiper is 62 km (39 miles) in diameter
Incidence Angle: 78.1°
Emission Angle: 28.0°
Phase Angle: 106.1°

Photo credit:

A Northern Footprint

The X-Ray Spectrometer (XRS) on MESSENGER collects compositional information for relatively large regions on Mercury's surface, and strong signals are only received during times of high solar activity. The blue region outlined in this wide-angle camera image mosaic shows the region visible to the XRS during a solar flare on 16 April 2011. The XRS data indicates that the area is basaltic in composition, the same type of volcanic rock that comprises the lunar maria. This region is part of the vast, high-reflectance northern plains that cover approximately 6% of Mercury's surface. The 1000, 750, and 430 nm bands of the Wide Angle Camera are displayed in red, green, and blue, respectively.

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

Messenger's First Solar Day

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

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

A View Towards the Plains

This view was captured as MDIS pointed to the east, which is oriented as the top of this image. Smooth plains extend into the distance, while the closer ground near the bottom of the image is more heavily cratered and hence rougher in texture. This location is on the edge of volcanic smooth plains that covers a great extent of Mercury's northern region.

Date acquired: August 12, 2011
Image Mission Elapsed Time (MET): 221626724
Image ID: 622112
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: 62.40°
Center Longitude: 321.6° E
Resolution: 242 meters/pixel
Scale: The bottom of this image is 220 kilometers (140 miles) across
Incidence Angle: 82.5°
Emission Angle: 59.4°
Phase Angle: 142.0°

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

Double Ring Impact Basin

This image shows a double ring impact basin with a smaller, younger crater superimposed on its rim. Larger impacts, such as the one that created this basin, form ring structures instead of central peaks.

Date acquired: June 02, 2011
Image Mission Elapsed Time (MET): 215511113
Image ID: 329264
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -80.35°
Center Longitude: 212.0° E
Resolution: 255 meters/pixel
Scale: The large impact crater is ~165 km (102 mi) in diameter.
Incidence Angle: 81.6°
Emission Angle: 0.9°
Phase Angle: 82.2°

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

Debussy Crater Rays and a Cosmic Ray

The rays apparent in this spectacular limb image of Mercury come from Debussy, the sharp crater near the terminator. This dominant crater on Mercury was also a part of MESSENGER's historic image of Mercury - the first image ever to be taken from a spacecraft in orbit about this planet. Readers may also notice a streak in the blackness of space in the top right corner of the image. This artifact was produced by a cosmic ray hitting the camera's CCD detector while the image was being collected.

Date acquired: July 26, 2011
Image Mission Elapsed Time (MET): 220137668
Image ID: 550504
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: -27.90°
Center Longitude: 29.17° E
Resolution: 2783 meters/pixel
Scale: Mercury's radius is approximately 2440 km (1516 miles)
Incidence Angle: 65.1°
Emission Angle: 48.2°
Phase Angle: 95.3°

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

Ts'ai Wen-Chi Crater and the Long Scarp

A long scarp runs vertically through the center of this image, deforming pre-existing craters along its length. At the bottom of this image, the scarp cuts through the wall and floor of the crater Ts'ai Wen-Chi (124 km diameter), named for the Han Dynasty poet and composer.

Date acquired: August 04, 2011
Image Mission Elapsed Time (MET): 220977824
Image ID: 591397
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: 27.73°
Center Longitude: 337.4° E
Resolution: 432 meters/pixel
Scale: This image is approximately 600 km (370 miles) across
Incidence Angle: 81.9°
Emission Angle: 38.2°
Phase Angle: 120.2°

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