Possible Volcanic Peak in Depression

Today's image is an anaglyph, which means if you have a pair of red-cyan glasses, you can see the image in 3D. While this peak, which is slightly over a kilometer tall, is located within a circular depression, it is much larger relative to the size of the depression than other central peaks that formed during impact cratering events on Mercury. Additionally, the feature has a distinctive red color signature, associated with sites of explosive volcanic eruptions on Mercury. Peaks such as this one are rare on Mercury, but there is a similar one nearby that also shares the same red color characteristics.

This image was acquired as a targeted set of stereo images. Targeted stereo observations are acquired at resolutions much higher than that of the 200-meter/pixel stereo base map. These targets acquired with the NAC enable the detailed topography of Mercury's surface to be determined for a local area of interest.

Date acquired: November 14, 2013
Image Mission Elapsed Time (MET): 26772351, 26772627
Image ID: 5197359, 5197360
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -8.50°
Center Longitude: 224.4° E
Resolution: 50 meters/pixel
Scale: This image is roughly 45 km (28 miles) across
Incidence Angle: 44.7°, 44.6°
Emission Angle: 14.2°, 24.6°
Phase Angle: 59.0°, 62.2°
Orientation: North is to the right, to enhance the 3D effect.

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

Volcanic Vents North of Rachmaninoff Crater

This beautiful view of the volcanic vents located to the north of the Rachmaninoff basin gives a new perspective on the area. At center, a vent is located within the bright pyroclastic deposit that is thought to have erupted from the vent. An older vent is also seen toward the bottom right as an irregularly shaped depression, though it has no clear surrounding deposit. The oblique angle of the image allows a view of the eastern walls of these features.

Date acquired: August 23, 2013
Image Mission Elapsed Time (MET): 19543205
Image ID: 4683301
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 7 (748 nanometers)
Center Latitude: 35.77°
Center Longitude: 63.90° E
Scale: The central vent is approximately 36 km (22 mi.) across.

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

Possible Volcanic Vent Near Discovery Rupes

The Caloris basin contains a complex mix of impact, tectonic, and volcanic features. At center-right, the elongate depression may be a volcanic vent within the basin. This feature highlights the ambiguity that sometimes arises in discerning whether a depression is due to an impact or a volcanic event, as both can leave elongate depressions. One clue that might point to volcanism is the depression's slightly irregular shape; another is the apparent lack of a rim of impact ejecta that is raised above the baseline level of the surrounding terrain.

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 200-meter/pixel morphology base map. It is not possible to cover all of Mercury's surface at this high resolution, but typically several areas of high scientific interest are imaged in this mode each week.

Date acquired: June 30, 2013
Image Mission Elapsed Time (MET): 14936140
Image ID: 4355811
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 24.18°
Center Longitude: 148.1° E
Resolution: 48 meters/pixel
Scale: The proposed vent is 17.9 km (11.1 mi.) across
Incidence Angle: 66.0°
Emission Angle: 50.3°
Phase Angle: 115.4°

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

Kipling Crater

The Kipling crater was originally circular, but that changed when the crater in this image was formed. Situated atop (and so postdating) the southern margin of Kipling, this smaller, younger crater has a distinctive central peak that is encircled by a curious, near-circular depression. This depression may be a volcanic pit, like others that dot the surface Mercury -- one of which even occurs in Kipling. The smooth floor of this crater shows subtle evidence of tectonic deformation, like that seen in many other infilled craters across the planet.

Date acquired: January 03, 2012
Image Mission Elapsed Time (MET): 234068866
Image ID: 1218101
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -20.83°
Center Longitude: 73.02° E
Resolution: 104 meters/pixel
Scale: This crater is ~88 km (55 mi.) in diameter
Incidence Angle: 67.2°
Emission Angle: 58.7°
Phase Angle: 28.2°
North is to the bottom-right corner of this image.

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

Lava Channels Near Kofi Crater

This image is a portion of the MDIS global mosaic basemap that was acquired during MESSENGER's first year in orbit. Of particular note is the flat-floored, southeast-trending valley in the center of the image, which starts near several depressions to the top left of the image, and connects with the Kofi crater (center right).

This valley is interpreted by MESSENGER team scientists as a broad lava channel, formed by the mechanical and thermal erosion of Mercury's surface by hot, low-viscosity, quickly-flowing lavas. The pits to the top left may be source vents for the lava flows that formed the channel; these flows then filled the Kofi crater at the channel's other end. Another lava channel, with a similar southeast trend, lies at the top right of the image, and there is a total of five broad channels in this region.

Determining how these channels formed, how rapidly they shaped the landscape, and how they relate to other volcanic features on Mercury -- such as expansive smooth plains nearby -- is important in understanding the role of volcanism on Mercury. Moreover, similar broad channels do not appear to exist elsewhere on Mercury, making this region a particularly interesting locale.

Date Created: February 10, 2012
Instrument: Mercury Dual Imaging System (MDIS)
Latitude Range: 54.3° N to 61.3° N
Longitude Range: 109.4° E to 121.6° E
Resolution: 146 meters/pixel
Scale: Kofi, the large impact crater at center right, is approximately 135 km (84 mi.) in diameter
Projection: Azimuthal equidistant

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

Red Mercury

Today's image shows a color view of the southern rim of the Caloris impact basin. The prominent reddish spots are associated with irregular depressions that are thought to be volcanic vents. The reddish deposits are probably formed of pyroclastic material ejected from the vents during explosive eruptions. The images were binned on the spacecraft from their original size of 1024 by 1024 to 256 by 256 pixels in order to manage space on the solid-state data recorder.

Date acquired: July 03, 2011
Image Mission Elapsed Time (MET): 218203157
Image ID: 458358
Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
WAC filter: 996-nm, 559-nm, 433-nm as red-green-blue.
Center Latitude: 13.61°
Center Longitude: 154.4° E
Resolution: 1896 meters/pixel
Scale: The edges of the image are about 490 km (300 mi.) long
Incidence Angle: 14.4°
Emission Angle: 13.5°
Phase Angle: 28.0°

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

Note: The title for this post is a play on another recent post, Blue Mercury.

Hesiod Crater

The crater at the western corner of this image is Hesiod. The northern and eastern parts of Hesiod's rim are marked by irregular depressions. These depressions are thought to be vents from which explosive (pyroclastic) volcanic eruptions originated. The high-reflectance areas on the wall of the crater just to the northeast of Hesiod and at the top of the image share color characteristics with other pyroclastic deposits known on Mercury. Pyroclastic eruptions are driven by volatile compounds, and MESSENGER has revealed that Mercury has a higher abundance of volatile elements than was previously expected.

Date acquired: September 07, 2011
Image Mission Elapsed Time (MET): 223922395
Image ID: 730933
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: -57.84°
Center Longitude: 329.6° E
Resolution: 193 meters/pixel
Scale: Hesiod crater is about 100 km (62 miles) in diameter
Incidence Angle: 62.7°
Emission Angle: 21.7°
Phase Angle: 84.5°

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

Volcanic Vent

This kidney-shaped depression lies along the inner margin of the Caloris basin and was first imaged during MESSENGER's first flyby of the innermost planet. The rimless, non-circular depression is the vent of a small, explosive volcano, similar to other volcanic vents on Mercury. The small number of superposed craters indicates that this feature is relatively young.

Date acquired: June 07, 2011
Image Mission Elapsed Time (MET): 215894570
Image ID: 347724
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 22.5°
Center Longitude: 146.1° E
Resolution: 28 meters/pixel
Scale: The depression is approximately 23 km (14 mi.) across its longest dimension.
Incidence Angle: 39.6°
Emission Angle: 45.5°
Phase Angle: 78.3°

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