NASA Probe Snaps First Photos of Mercury's Water Ice

The first-ever photos of water ice near Mercury's north pole have come down to Earth, and they have quite a story to tell.

The images, taken by NASA's MESSENGER spacecraft (short for MErcury Surface, Space ENvironment, GEochemistry, and Ranging), suggest that the ice lurking within Mercury's polar craters was delivered recently, and may even be topped up by processes that continue today, researchers said.

NEWS: Mercury Not Too Hot For Polar Water Ice?

More than 20 years ago, Earth-based radar imaging first spotted signs of water ice near Mercury's north and south poles - a surprise, perhaps, given that temperatures on the solar system's innermost planet can top 800 degrees Fahrenheit (427 degrees Celsius). [Water Ice On Mercury: How It Was Found (Video)]

In late 2012, MESSENGER confirmed those observations from orbit around Mercury, discovering ice in permanently shadowed craters near the planet's north pole. MESSENGER scientists announced the find after integrating results from thermal modeling studies with data gathered by the probe's hydrogen-hunting neutron spectrometer and its laser altimeter, which measured the reflectance of the deposits.

And now the MESSENGER team has captured optical-light images of the ice for the first time, by taking advantage of small amounts of sunlight scattered off the craters' walls.

NEWS: Spacecraft Raises Mercury Mysteries

"There is a lot new to be learned by seeing the deposits," said study lead author Nancy Chabot, instrument scientist for MESSENGER's Mercury Dual Imaging System and a researcher at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, in a statement.

For example, the texture of the ice at the bottom of Mercury's 70-mile-wide (113 kilometers) Prokofiev Crater suggests that the material was put in place relatively recently rather than billions of years ago, researchers said.

Images of other craters back up this notion. They show dark deposits, believed to be frozen organic-rich material, covering ice in some areas, with sharp boundaries between the two different types of material.

"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," Chabot said.

ANALYSIS: Earth Portrait to be Snapped from Saturn and Mercury

Earth's moon also harbors water ice inside permanently shadowed polar craters, but its deposits look different from those on Mercury, researchers said. This could be because Mercury's ice was delivered more recently.

"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," Chabot said. "This will be a very interesting line of inquiry going forward."

The new study was published online today (Oct. 15) in the journal Geology.

More from SPACE.com:

Planet Mercury: Simple Facts, Tough Quiz Most Enduring Mysteries of Mercury NASA's Messenger Mission to Mercury (Infographic)

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Kandinsky crater lies near Mercury's north pole, and may have hosted water ice. MESSENGER spacecraft's Wide Angle Camera broadband image appears at left, outlined in yellow, and superimposed on an MDIS polar mosaic. The view on the right shows the same image but with the brightness and contrast adjusted to show details of the crater's shadowed floor. Image released Oct. 15, 2014.

The Solar System's Innermost Planet Welcomes a Visitor

Mysterious Mercury, the closest planet to the sun and smallest planet in the solar system, is now being orbited by a robotic satellite for the first time in history. NASA's MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) spacecraft finally arrived after a "near perfect" (according to mission managers) orbital insertion on March 17, 2011. This was the culmination of an epic six year, 4.9 billion mile, journey that took messenger on a gravitational roller coaster ride through the planets of the inner solar system and three flybys of Mercury, all in an effort to slow the spacecraft down as it fell deep into the sun's gravitational well. Now that MESSENGER is comfortably in orbit, it has opened its eyes and started to photograph the surface of Mercury in glorious detail. Here are the first photographs from Mercury orbit...

A Colorful View

MESSENGER beamed the first ever black and white photograph of Mercury's cratered surface back to Earth on March 29, but that wasn't the only shot. It was actually part of an eight-image sequence taken through MESSENGER's Wide Angle Camera (WAC). In this image of the same view, the red, green and blue filtered images have been superimposed to generate a color photograph. The use of color helps the science team discern variations in composition of Mercury's surface. The large crater in shot is called "Debussy," and to give a sense of scale, the crater measures approximately 50 miles across.

Craters of Interest

An annotated photograph of the region surrounding Debussy crater. Another crater named Matabei can be seen. Strangely, Matabei exhibits dark impact ejecta, or "rays." This is in sharp contrast to the bright rays emanating from the larger Debussy crater. The reasons for these contrasting rays will be explored by the MESSENGER mission.

Crater Close Up

Using its Narrow Angle Camera (NAC), MESSENGER has captured a close up of the bright impact ejecta and secondary craters radiating from the primary impact crater of Debussy. This level of detail of Debussy has never been seen before. As noted by MESSENGER during its second flyby of Mercury in 2008, Debussy's rays extend for hundreds of miles.

Laser Elevation

The spacecraft also carries the Mercury Laser Altimeter (MLA) that measures the elevation of Mercury surface features. In this plot, the altitude profile of the planet has been plotted for two MESSENGER orbits. As can be seen, surface features vary by around 6 kilometers (3.7 miles) from lowest trough to highest peak. A variety of features have been plotted, including several craters. Both orbital passes have been offset by 3 kilometers for clarity.

Mercury's Magnetism

One of the biggest puzzles about Mercury is that of its planet-wide magnetic field. Why would such a small planet have such a strong magnetic field when the larger planets Mars and Venus do not? This plot represents the measurements taken by MESSENGER's magnetometer over 10 successive orbits.

North Polar Region

As it made a low pass over Mercury's north polar region, MESSENGER managed to pivot to capture this image of smooth plains punctuated by craters with its Wide Angle Camera (WAC). These deep craters will be of increasing interest to scientists as they investigate the possibility of water ice in their shaded, frozen interiors.

Never Before Seen Terrain

A never before seen region near Mercury's north pole. The image was captured from an altitude of approximately 450 km (280 miles).

Colorful Terrain

The Wide Angle Camera (WAC) can capture images of Mercury's surface through 11 colors. By doing this, the surface composition can be analyzed. For example, some minerals such as olivine and pyroxene often absorb more light at longer wavelengths than at shorter ones, so the MESSENGER team will be keeping a lookout for the absorption signature for minerals such as these.

The View

Sometimes, when not looking directly below, images of Mercury's limb (or horizon) will be captured by MESSENGER's Wide Angle Camera (WAC), reminding us that this little spacecraft is orbiting this little world.