New Mercury Images Show Shadowed Craters and New Terrain

Hundreds of spectacular new images of Mercury are pouring in from the first spacecraft ever to orbit the smallest planet.
NASA’s Messenger spacecraft took its first shot of Mercury early yesterday morning, and sent 224 more images to Earth by the end of the day. In its first three days of shooting, Messenger will collect 1,500 images, exceeding the number of photos taken by all the earlier flybys combined.
“That’s just the barest hint of what we’ll have on a regular basis once the mapping phase begins” on April 4, said principal investigator Sean Solomon in a press conference March 30. “This extremely dynamic planet will be on continuous display for the first time.”
This gallery showcases the first detailed peek at the hot, scarred, underexplored world at the solar system’s inner edge.

First Look

The first-ever image from orbit released yesterday was actually one of eight images taken through several different filters. Each filter lets in a different wavelength of light, letting planetary scientists piece together colored versions of the images. In the above image, wavelengths of 1000 nm, 750 nm, and 430 nm are displayed in red, green, and blue, respectively.
The first image caught sight of terrain that had never been seen before, plus several bright craters and the south pole.

Clair de Lune

This image features a young crater called Debussy, named for the French composer Claude Debussy who wrote “Clair de Lune” (“Moonlight”). Mercury does look a lot like the moon in these first images, with gray terrain interrupted by impact craters.
“Don’t be deceived by the images alone,” Solomon said. “The chemical makeup, interior structure, and interior dynamics are all quite different.”
Debussy crater is 50 miles wide. Its bright color tells astronomers that it formed relatively recently, probably in the last billion years. Mercury’s surface is darkened by the constant bombardment of tiny meteoroids and charged particles from the solar wind and Mercury’s own magnetosphere. Bright craters like Debussy haven’t been around long enough to grow dark, Solomon said.
“Time will darken the rest of the surface,” he said. “It is their brightness that identifies them as being younger than the rest of the terrain.”

North Pole

This image shows a region near Mercury’s north pole that had never been seen before. Most of these craters are probably secondary craters, formed from chunks of rock and dirt that were tossed out of a bigger crater when it formed.
“This is a heavily cratered surface, but it may have all happened on one really bad day,” Solomon said.
Messenger’s orbit takes it almost directly over Mercury’s poles, giving the first view into heavily shadowed polar craters. In the 1990s, Earth-based radio telescopes gave tantalizing hints that these craters could harbor water ice.
“It’s a hypothesis we’ve been aching to test for 20 years,” Solomon said. “We’ve finally started imaging and other measurements that will be able to peer into those crater floors.”

Craters in Color

Messenger’s wide-angle camera (WAC) has 11 different filters to build colored images of the Mercury’s surface (although because these images take up so much of the spacecraft’s on-board memory, most of the color images will use only eight filters). Different colors often correspond to different chemical compositions on the surface. This image of part of Mercury’s northern hemisphere shows how craters expose different colored material, hinting that Mercury’s upper surface and its interior layers are made of different stuff.

Closing In

Because color images are actually eight or more individual shots laid on top of one another, they are lower resolution than grayscale images. Color images give information on the surface composition, but high-resolution images give the details that help decipher what shaped the landscape.
Messenger’s narrow-angle camera (NAC) has a field of view seven times smaller than the wide-angle camera, giving sharper views of the same regions. This image is a close up of the historic first-ever image.
“We need both kinds of images,” Solomon said. “They complement each other wonderfully. It’s wonderful that we have both and they’re both working well right now.”

More Than A Pretty Face

The cameras are hardly Messenger’s only eyes. The orbiter has a suite of seven science instruments that will work in concert to measure Mercury’s magnetic field, tenuous atmosphere, surface composition, interaction with the sun and more.
This diagram shows measurements of the strength of Mercury’s magnetic field measured on 10 successive Messenger orbits. These observations will help trace the geometry of Mercury’s magnetic field, which will help astronomers figure out how Mercury managed to hold on to a global magnetic field while larger planets like Mars and Venus did not.
“What impresses me is that in a span of 5 days, from orbit, Messenger tripled the number of observations of the planetary magnetic field” available from the 1970s Mariner 10 mission and Messenger’s own flybys of Mercury, Solomon said. “We are rapidly ramping up a much larger data set with which to characterize the geometry of Mercury’s magnetic field.”

Last Horizon

Messenger took this beautiful shot of the edge of Mercury’s disk on the first orbit for which the cameras were turned on. But now that Messenger is in orbit, views of the horizon will be much less common.
The Messenger mission marks another sort of horizon for solar system exploration. It’s the last of the inner planets to be explored in detail, and it will be at least a decade before we can say again that we’re seeing part of a solar system planet for the first time.
“The last of the classical planets, the planets known to the astronomers of Egypt and Greece and Rome and the far East, has finally reached the stage where mankind has put a spacecraft in orbit,” Solomon said. “It’s a wonderful thrill to link that not-particularly-bright dot in the sky with the images that we’re now seeing downlinked from Messenger spacecraft.”

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

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